Understanding Microbial Nutrition and Growth

Hey everyone, Dr. D here and in this video we are going to be covering chapter 9 from our Microbiology a Systems Approach 7th edition. This chapter covers microbial nutrition and growth. So let's go ahead and get started. Alright, let's get started with this exciting chapter covering microbial nutrition and growth. So, just like you and me, we need nutrients in order to grow. Microbes are no different. They need a source of nutrients in order to grow and develop and to divide. And so this chapter talks about the different microorganisms and where they obtain their nutrition from. So, first of all, what... is nutrition. Nutrition requires nutrients. Nutrients are acquired from the environment and used for cellular activities. These activities, like I said, include growth and division. Organisms require a constant influx of certain substances from their habitat to fulfill their dietary needs. And the source of the particular elements, their chemical forms, and how much of the element is needed varies among different types of organisms. We're going to be talking about the different elements, the different molecules, the different nutrients that these organisms need in order to grow. And here you can see a list of different elements from the periodic table of elements. We have different elements that... are required by all living organisms, carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulfur, and so on and so forth. There are also a host of other elements that we need in trace amounts, in minute amounts as well. So we're going to talk about these different elements. We're going to talk about which ones of these elements make up our biomolecules. you know, where we source these from and where microorganisms source these elements from. So again, we have certain nutrients that all organisms require. Essential nutrients are substances that must be provided to an organism. For instance, all organisms require carbon, hydrogen, oxygen, nitrogen. phosphorus, and sulfur. All organisms require these handful of elements because these are the central elements to our major biomolecules. And I'll show you what the biomolecules are in a little bit. Macronutrients refer to the nutrients that are required in relatively large quantities. So for instance, carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur are all macronutrients. macronutrients. Micronutrients, on the other hand, also known as trace elements, are required in small amounts or minute amounts. So for instance, you know, you require copper, zinc, you require iron in your diet. These would be trace elements required. And a lot of times, these trace elements, they serve as cofactors. They are involved in enzyme function and maintenance of protein structure. So for instance, remember what a cofactor is? A cofactor is an enzyme helper or a protein helper. A cofactor binds to an enzyme or a protein to allow it to function correctly. So for instance, hemoglobin in your blood requires the cofactor iron in order to properly transport oxygen. Inorganic nutrients, as their name suggests, are nutrients that lack carbon. Organic nutrients, these are nutrients that contain carbon plus hydrogen. Common inorganic nutrients are elements like iron, zinc, sulfur, potassium. Common organic nutrients include things like vitamins or growth factors. Here we can see some of the principal inorganic elements and their reservoirs. The reservoirs mean where they obtain their elements from. So organisms can obtain their carbon either from the air in the form of CO2 or from rocks and sediments. Organisms can obtain their oxygen either from the air, certain oxides, and water. So I'm not going to go through this entire list, but it gives you an idea of where microorganisms can obtain their elements, the reservoirs that... harbor these elements and where they can obtain these elements. Now, what is the chemical composition of a bacterial cell? Because by looking at what a bacterial cell is comprised of, we can glean, we can understand from that the nutritional requirements of that bacterial cell. Well, it turns out about 70% of the cell content is water. And that makes sense. Most of your body weight is water as well. And then the proteins are the next most prevalent chemical. So when we subtract the water weight of a cell, the remainder is known as the dry cell weight. Imagine taking a bacterial cell and completely dehydrating it, removing all water. Well, you would remove 70% of the bacterial cell's weight. But what's left over is the dry cell weight. And 97% of the dry cell weight is composed of organic compounds. This means the molecules that have carbon and hydrogen as well. Now, 96% of the dry weight is composed of only six elements. Remember these six elements? I called them chomps, right? Um, carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. These, these six elements alone make up 96% of the dry weight of the cell. And that's why these are definitely macronutrients, nutrients that are required in relatively large amounts by the cell. Again, proteins make up only 50% of the dry weight of the cell. 15% of the total weight of a bacterial cell such as Escherichia coli, but it makes up 50% of the dry weight of the cell. RNA makes up 20% of the dry weight. DNA makes up 3% of the dry weight of the cell. Carbohydrates make up 10. Lipids make up 10. And then miscellaneous make up the remainder 4. These are the organic compounds. So by the way, these major organic compounds are known as biomolecules. Proteins, RNA and DNA. By the way, the RNA and the DNA are known as nucleic acids. Then you have the carbohydrates and the lipids. These are biomolecules. And the biomolecules make up the majority of the dry weight of the cell. What about inorganic molecules? Inorganic molecules only make up about 1% of the total cell's weight, while water, remember, makes up 70% of the cell's weight. Water is abundant in all living cells. Again, we can have a breakdown on the right here of various elements and their contribution to the dry weight of the cell. Remember, the macronutrients, the macronutrients, are required in relatively large amounts in the cell, while the micronutrients are required in lower quantities in the cell. A major way that organisms are categorized based on their nutritional requirements has to do with where they obtain their carbon. This is known as their carbon source. Consumers like you and me are known as heterotrophs because we obtain our carbon from organic compounds that we ingest. Just think about it. Where do you think you get your carbon from? Remember, we need a large source of carbon in our nutrition, in our diet, because carbon is the most abundant element in our dry mass of our cells. So where do we get our carbon from? Well, don't we eat breakfast, lunch, and dinner? We obtain our carbon from our diet, from things we eat, organic molecules that we consume. So these organisms that get their carbon from organic molecules they consume are called heterotrophs. So you and I, we are heterotrophs. We obtain our carbon from organic molecules. And this means that we are dependent on other life forms. We cannot feed ourselves. We need to consume other organisms to obtain carbon molecules. Conversely, autotrophs are organisms that obtain their carbon from CO2 from the air. There is CO2 floating around in the air. And autotrophs can actually capture inorganic CO2 as their carbon source. That's where they get their carbon from. It's a process known as carbon fixation. If any of you have studied photosynthesis in the past, you know that CO2 is a carbon source. that during the Calvin cycle, CO2 is captured from the air and that's known as carbon fixation. So can you and I, let's see if you can beat Wicket. Can you and I undergo carbon fixation? Can we take CO2 out of the air as our source of carbon? That's right, Wicket. Wicket is so smart. We cannot, right? Because, you know, this is what plants do. Plants have chloroplasts. They've got the ability to capture CO2, right? And photosynthetic organisms can capture CO2 from the air. They are autotrophs. And because they can capture CO2 from the air and they don't require other organisms, they don't have to eat other organisms. They're known as self-feeders. These are the producers in the environment, in ecology. When we're talking about the ecosystem, the autotrophs are the self-feeders. They don't have to consume other organisms to live. And because of that, they tend to be producers. They are at the bottom of the food chain. They're the source of the organic molecules for the rest of us, us heterotrophs. And once they obtain that CO2, they can convert that CO2 into other carbon compounds like sugars or different biomolecules. Without these autotrophs, we would have nothing to eat. The food web would collapse. The ecosystem would have no way of sustaining itself and it would collapse. The autotrophs are at the bottom of every food web and they are the producers in the ecosystem. So without autotrophs, there would be nothing for heterotrophs to consume and we would perish as heterotrophs. Now, moving on to nitrogen sources. Remember, nitrogen is another macro element that microorganisms need in large amounts. Nitrogen can be sourced from the air. Some organisms, these are known as nitrogen fixers. Some organisms can actually take nitrogen from the air, and that's a good resource. And the air is actually a great source of nitrogen, seeing as how 79% of the atmosphere is basically made up of nitrogen. So some organisms can actually capture nitrogen from the air, and these are known as nitrogen fixers. Now, you and me, we obtain our nitrogen from our diet. We consume other organisms, so we're eating their proteins, their DNA, their RNA, their ATP, and that's where we source our nitrogen. And now, what about microorganisms such as E. coli? Where do they get their nitrogen from? Well, some bacteria and algae utilize inorganic nitrogenous nutrients such as NO3 minus, this is nitrate. NO2 minus, this is nitrite. Or NH3, this is ammonia. These are three common sources of nitrogen for microorganisms. So if you can't fix nitrogen from the air, you can always gain it from your environment in the form of these three molecules, these three inorganic molecules. Next, what about... oxygen sources. Where do we get oxygen from? Well, first of all, oxygen makes up 20% of the atmosphere. So that's one source of oxygen, but also from your diet or from the environment as well. How about hydrogen sources? Well, we can get hydrogen from our diet, from biomolecules that we consume. Plants get their hydrogen from water. They can actually remove hydrogen atoms from water molecules. And hydrogen is important in oxidation reduction reactions in the cell, such as photosynthesis and cellular respiration. Without hydrogen, without access to easy hydrogen elements, photosynthesis and cellular respiration would not. be possible. What about a phosphate source or phosphorus source? Where do we get those? You and I obviously get our phosphorus from our diet, the molecules we eat, but there are other inorganic sources of phosphate. So for instance, in mineral deposits from soil and such, microorganisms can obtain their phosphate from their environment in the form of these If these deposits and what about sulfur? Remember, sulfur is a macronutrient as well. Well, it's widely distributed throughout the environment, rocks and sediments. So it's it's easy to find it in the environment. It is an essential component of vitamins such as vitamin B1, and it's required in two of the 20 amino acids, methionine and cysteine. What about essential organic nutrients? Remember I said organic nutrients include the vitamins and the growth factors. So these organic nutrients such as amino acids, nitrogenous bases, vitamins that cannot be synthesized by an organism, they must be provided by the environment. Now another way that organisms are categorized based on their nutritional types is how they get there. energy. Organisms that get their energy from sunlight are known as phototrophs, while organisms that obtain their energy in the form of chemical compounds, either organic chemicals or inorganic chemicals that they consume, these are known as chemotrophs. So let me ask Wicket, let's see if you can beat Wicket. Which one are we? Are we phototrophs or chemotrophs? That's right, as always, Wicket. We are chemotrophs. We are organisms that obtain our energy from chemical compounds that we consume. And so heterotrophs tend to be chemotrophs for the most part. We are chemotrophs. We obtain our energy from chemical compounds that we consume. Photo trophies, on the other hand, these would be your photosynthesizers. These would be organisms like cyanobacteria, algae, plants, trees, photosynthetic organisms. These are the organisms that obtain their energy from sunlight. So let's bring these concepts together then. What do you think a photo autotroph is? Well, remember, let's break down this term. Photo means... an organism that obtains its energy from sunlight. And auto means an organism that obtains its carbon from CO2. So a photoautotroph would be something like a plant or a cyanobacteria or algae, an organism that obtains its energy from sunlight and its carbon from CO2. What about a chemoheterotroph? A chemoheterotroph, remember chemo, means an organism that obtains energy from molecules that it consumes. And heterotroph means that it's an organism that obtains its carbon in the form of organic molecules. So a chemo-heterotroph gets its energy from molecules that it consumes, and a heterotroph is an organism that contains its carbon in the form of molecules. form of organic molecules. Did you know that there are organisms that can mix things up a little bit? So for instance, a chemoautotroph, a chemoautotroph would be an organism that gets its energy from molecules that it consumes. But autotroph refers to an organism that gets its carbon from CO2. There are microorganisms that can do this. There are chemo-organic autotrophs and chemo-litho autotrophs as well. Chemo-organic autotrophs use organic compounds for energy, but inorganic compounds as a carbon source, while chemo-litho autotrophs require neither sunlight nor organic nutrients and rely totally on inorganic materials. How can they do that? They can remove electrons from inorganic substrates such as hydrogen gas, hydrogen sulfide, sulfur, or iron. So the point of this slide is to show you that there's quite a diversity in nutritional types. So just because you're familiar with plants and animals, that doesn't mean that all organisms, especially microorganisms, behave in the same way. There are Organisms that are quite diverse in their nutritional requirements, they can get their nutrition in very distinct and different ways. Energy cannot be used in the form of sunlight or these chemicals like sugars and fats. So organisms undergo a process known as cellular respiration, oftentimes aerobic. cellular respiration. You may have learned about this in Biology 1406. This is the process by which glucose and oxygen become CO2, water, and ATP energy. Microorganisms use oxygen in this process and some microorganisms can use a molecule other than oxygen in this process as well. Either way, this is the process by which many animals, protozoa, fungi, and bacteria obtain their ATP. And remember, ATP is the energy currency of the cell. Now, when an organism is considered a saprobe or a saprobic organism, these are known as the decomposers. These organisms can decompose plant litter, animal matter, dead microbes, anything that's dead organic matter. These organisms are important for recycling nutrients in the environment, in the ecosystem. Usually when we're talking about saprobes, these decomposers, we're referring to bacteria and fungi. Fungi are probably the best known saprobe organisms. The way these organisms work... is that they cannot engulf the large organic molecules. Instead, they release enzymes that break down that organic matter, and then they transport the broken down organic matter into the cell. Here you can see what I'm talking about. This is a bacterial cell or a fungal cell. This is a saprobe right here in green. This is a decomposer. This out here represents... The organic debris, large organic debris. Now, again, the bacteria will feed on this debris, but the bacteria can't internalize these large pieces of debris. So what the organism does is it releases these hydrolytic enzymes, enzymes that are capable of breaking down organic matter, and then transport these broken down nutrients into the cell. So you see. You can then absorb those raw components, those sugars, those fats, those nucleic acids, those amino acids, etc. into the cell. And this is how decomposers work. Many of these decomposers are obligate saprobes, which means they must feed off of dead organic material. However, some of these organisms can be facultative parasites. which means that they are capable of feeding off a host. Think of a fungal infection, right? There are human fungal infections. In that case, the fungus is a parasite on you, the host. That's what a parasite does. A parasite becomes dependent on the host for its nutrition. So when I say parasite, think of something that becomes dependent on the host on which it lives for its nutrition. parasites, again, they live on or in the body. They can cause some degree of harm. Different parasites can cause different degrees of harm. Some parasites, you may not even know they're there like a tapeworm, but it still causes harm because it depletes nutrients from the host. And you know, it also inserts its hooks into the gut lining, which can cause an infection. So, you know, a tapeworm is one of the more mild. parasites but then there are parasites that cause a lot of damage a lot of disease and can cause death even hi gizmo hey gizmo has come to visit you guys i got him gizmo say hi oh no that's wicked Wicket has come to say hi, people. Yay! Everyone loves a Wicket. Hi, Wicket. Thank you for visiting, buddy. Okay. All right. He's going off to bed, I think. Awesome. Well, we always enjoy visits from Wicket. I thought it was Gizmo, but Gizmo's in his bed right here. Parasites are considered pathogens because they can cause damage to host. tissues and can sometimes even cause death to the host. These parasites can range from viruses to worms. So there are many different organisms and small infectious agents which are considered parasites. An obligate parasite is unable to grow outside of the living host. And an obligate intracellular parasite is a parasite that must spend at least part of its life inside of a host cell. That's what intracellular means, by the way, inside of the cell. So if it's an intracellular parasite, this parasite lives and feeds inside of your cells, whereas other parasites might live among your cells or on your tissues. Now, most microorganisms especially single cell ones, they lack a mouth, right? Like you and I have a mouth and a digestive tract. So how did these bacteria, for instance, how do they get their nutrition? Well, it's called nutrient absorption. The necessary nutrients must be taken into the cell and then waste materials must be transported out of the cell. So this requires what's called transport. Things need to be transported into the cell and out of the cell through the cell membrane. To understand how substances get into the cell or out of the cell through the plasma membrane, we need to remember this concept of diffusion. Diffusion is a spontaneous process. It does not require energy. In fact, diffusion releases energy. Diffusion is simply the movement of molecules in a gradient from an area of high density or concentration to an area of low density or concentration. So if I, for instance, if I release a gas right here, that gas will spontaneously diffuse through the room. It will go from an area of high concentration where I release the gas to an area of low concentration. you know, the rest of the room. And that's a spontaneous process. It does not require any energy to occur. If you remember from earlier biology classes, this would be known as a spontaneous or negative delta G reaction. Spontaneous reactions do not require energy. And diffusion is an example of something that does not require energy. It's a spontaneous process. So for a substance to diffuse across the cell. membrane or plasma membrane, this, if it's happening by diffusion, then it does not require energy. Next, let's discuss osmosis. Osmosis is simply the diffusion of water across a membrane, a selectively permeable membrane. That's all osmosis means. Remember that a membrane is select or differentially permeable. This means that not just anything can enter the cell and not just anything can float out of the cell. The cell can determine what can enter the cell or what can exit the cell. Remember from earlier biology classes, if you had them, that when a membrane is placed between solutions of different concentrations, and the solute is larger than the pores, then water will diffuse at a faster rate from the side that has more water to the side that has less water until equilibrium is reached. So let me explain how osmosis works. Osmosis is diffusion of water across a selectively permeable membrane. So now let's take a look at this example from your book. Here we have solute. And remember, solute is the substance that's dissolved in the water. And then you have the solvent, which does the dissolving. This is the water. Here you can see an example where we have a semi-permeable membrane. Outside in the environment, we have pure water. And inside of that membrane, we have water. plus the solute sugar. Let's pretend these dots represent sugar. These red dots represent sugar. If we take a close look at the membrane, it is a selectively permeable membrane because it is permeable to water. However, it is not permeable to the sugar. This means that the sugar cannot cross the membrane, but the water can. Now let me ask you this and let me see if you can beat Wicket. Which way, if the water is the only component that can move across the membrane, not the solute, which way will the water travel from the environment into the cell or from the cell into the environment? Let's see if you can beat Wicket. That's right. Hopefully you got it correct, just like Wicket. And that means, yes, the water flows into the cell. The water is more concentrated out in the environment. The water is less concentrated in this cell. And so the water will travel from where water is more concentrated to where water is less concentrated. Whatever is moving across the membrane, whatever is diffusing will diffuse from where it is high in concentration to where it is low in concentration. If these pores were larger. then the sugar, the red dots, would diffuse out of the cell. They would go from in to out because the sugar is more concentrated inside than outside. But remember, the sugar cannot cross the membrane because the pores are too fine. The membrane is selectively permeable. And so the water is what's mainly crossing the membrane. If that's true, the water will move from where water is more concentrated to where the water is more concentrated. to where water is less concentrated. And yes, if you're curious, whichever way the solute would like to go, whichever way the solute would like to diffuse, the water always wants to diffuse the opposite direction. So yes, whichever way one wants to go, the other one always wants to go the other direction. Remember, just like this example here, the cell itself has a number of solutes inside. versus its environment. Sometimes the microorganism can find itself in an environment that has less solute concentration than inside. And sometimes the organism can find itself in an environment with more solute concentration than inside. And sometimes the organism is in an environment with the equal amount or equal concentration of solute inside and outside of the cell. These are known as tonicity environments. Tonicity problems are osmosis problems. It's water which is crossing the membrane into the cell, out of the cell, or having no net flow in or out of the cell. I have a nice short video I would like you to watch. I'm going to throw up a card. Uh, here, I'm going to throw up a card here and that will direct you to my review on tonicity. And it's a thorough tonicity review. I assume that most of you who have taken this class have also taken biology 1406, where we talked deeply about tonicity and how the environment can affect a cell. If not, please go ahead and watch that video so that you are brought. up to speed and then meet me back here so that we can review how tonicity affects microorganisms. I'll wait for you here. In fact, this might be a good break time with Gizmo and Wicket. That way you could go watch that video and I can hang out with my cats. All right, we'll reconvene in just a minute. Welcome back from break time with Gizmo and Wicket. Let's get back into this review of tonicity problems. Hopefully my short review video helped you and you remember the concepts of diffusion, osmosis, dialysis. You understand. isotonic, hypotonic, and hypertonic conditions. That's great. So let's do a quick review right here. In an isotonic solution, that's this example on the left, if we're dealing with a type of cell wall-less cell, this is a cell without a cell wall, such as an amoeba or a paramecium. In an isotonic environment, there's equal concentration of solute inside of the cell as outside of the cell. The solute is depicted here in green. And the solvent is water. You can't really see the water, but you can imagine it's surrounded by water. In this case, remember, for every one water molecule that enters the cell, about one water molecule leaves the cell. So there's no net flow of water. In this case, the cell will neither gain nor lose net water volume. Here, this is a bacterial cell. Remember back... Bacterial cells typically have a cell wall here depicted in pink, a cell wall of peptidoglycan. And that cell wall is in addition to the plasma membrane, it's strengthening the cell. In this case, again, there's an equal solute concentration outside as inside. Again, it's an isotonic solution. So water should not net flow into the cell, nor should water net flow out of the cell. We are at equilibrium. Either way, the cells are intact. The cells are healthy. Now let's discuss what happens in a hypotonic solution. This means a solution with a lower solute concentration in the environment. Hypo means low. Hypotonic solution means a low solute solution. In this case, you have a lot. more solute. So you see the green dots here. For instance, I'll give you an example like salt. Let's say these green dots represent the solute salt. And you see how there's a higher salt concentration inside of the cell versus outside of the cell. This is known as a hypotonic environment. In this case, water, remember, solute cannot leave the cell. Solute cannot enter the cell. These are tonicity problems, which means they are osmosis problems. So only water can flow. The solute can't leave the cell. So water will enter the cell. Water will flow from where water is more concentrated outside of the cell to where water is less concentrated inside of the cell. And if you don't have a cell wall to protect you from, you know, this volume increase, then that osmotic stress will lyse the cell. The cell will actually break apart and get destroyed. Lysis means to break. The cell will lyse. However, a bacterial cell in a hypotonic solution will fare differently because when water flows into the cell, the cell will swell up. However, it won't pop. Do you know why it won't pop? Let's see if you can beat Wicket to the answer. Hey, Wicket. Why does this cell not pop? Exactly right, Wicket. It's that tough cell wall, that ptidoglycan cell wall. That cell wall is so firm that it prevents lysis of the bacterial cell. Same thing in plants. You know, in plants, plants can also withstand hypotonic solutions or environments because plants have a cell wall of cellulose and that prevents them from exploding. By the way, you want to know a fun fact? Do you know how penicillin works? You know how penicillin is a potent antibiotic against certain bacteria? Well, the way penicillin works is that it compromises the cell wall. You see this cell wall in pink? Well, that cell wall is compromised by penicillin. Penicillin prevents the cell from maintaining its cell wall. And then guess what happens if a bacteria... bacterium can't maintain that cell wall of peptidoglycan, it's compromised, and then the cell will lyse. Isn't that interesting? So that's how penicillin works. Now our last example here, a hypertonic solution. Remember, this is an environment that has a high solute concentration compared to the cell. So here you can see there's a lot more salt, a lot more solute outside of the cell in the environment than inside. In this case, again, the water will flow from where water is more concentrated inside of the cell to where water is less concentrated outside of the cell. And that results in the cell shriveling up like a raisin. And this is known as a shriveled. cell or also known as a crenated cell now cells that have a cell wall they also shrivel but it's not the cell wall that shrivels notice how the cell wall did not change much it might be less bloated right the cell wall does not shrivel however the plasma membrane see here the plasma membrane in yellow the plasma membrane which should be pressed against the cell wall, is now peeling away from the cell wall. See how the plasma membrane has peeled away from the pink cell wall? And so it's the plasma membrane that's shriveling up because of the water loss. Water is net diffusing out of the cell. This makes the plasma membrane peel away from the cell wall, resulting in what's known as a plasmalized cell. This is a plasmalized cell. A plasmalized cell is a cell where the cell wall is intact, but the plasma membrane has peeled away due to efflux of water in that hypertonic environment. Now recall that diffusion is a spontaneous process. Diffusion occurs without energy input. It is a negative delta G reaction. It's exergonic. And so anytime you see the term diffusion, you should think that no energy is required for that process to happen. If a substance diffuses across the membrane itself, this is known as simple diffusion. And this is a type of transport. because you're transporting a substance across the membrane. And this is known as a type of passive transport. Passive meaning no energy is required. So simple diffusion of a substance would be if a substance diffused across the membrane, directly across a membrane. And this is an example of passive transport because no energy was required to transport that substance into the cell. So for instance, if oxygen diffuses into a cell, that's passive transport. That's simple diffusion. If CO2 diffuses out of a cell, that's simple diffusion. Again, a type of passive transport. No transport protein is required for simple diffusion, passive transport across a cell. However, if a molecule is... polar or charged, polar meaning it has partial negative ends or partial positive ends, or charged as in ions like sodium cation or chloride anion. In that case, for it to diffuse and transport across the membrane, it requires a transport protein. So let's pretend that this molecule here, this molecule in purple, let's pretend that's glucose. or water, which is a polar molecule, or let's pretend it's sodium cation or chloride anion. These substances cannot simply diffuse across a membrane because of the polar, the non-polar region here. These tails are non-polar. That means that polar and charged substances need to travel through transporters to get into the cell. Because a transporter is required for this type of diffusion, this type of transport, those proteins are facilitating the diffusion, and this is known as facilitated diffusion. Facilitated diffusion. Facilitated diffusion, unlike simple diffusion, requires a transport protein to allow the polar or charged ion across the membrane. Again, though, it's a type of diffusion, so that means no energy is required. So it is also an example of passive transport. Now, if you want to move a substance against the concentration gradient from low concentration to high across the membrane, this is known as active transport, and it's going to require energy. Energy is required. Energy is required for active transport. transport. Moving a substance from low concentration to high, that means you're going against diffusion and that would require energy. That would not be spontaneous. Here we can see an example of active transport. Imagine if these thumbtack looking things are some molecule and you're trying to expel that molecule where there's already a high concentration of these molecules outside of the cell. There's a lower concentration of these molecules inside of the cell and you're transporting these molecules out to where they're already high in concentration. Again, this would be an example of active transport, and it would not occur without ATP energy or some other form of energy. In this case, you can use that energy in order to move a substance against the concentration gradient. That means against the force of diffusion. Now, this other concept of group translocation, we're not going to delve too much into it, but it simply means that when a substance is transported across the membrane by a facilitator, by a transport protein, it's modified along the way. Notice how these pink substances, they picked up a green square on the way in. That means that the substance was modified upon transport across the membrane. Well, that's what group translocation means. And usually this modification is a phosphorylation, like this. pink molecule picked up a phosphate group, for instance, but it could be other things as well. Now, for the last type of transport that we're going to talk about, this is another form of active transport, but it's called bulk transport. Bulk transport, because you are bringing bulky items into the cell, or you are expelling bulky items out of the cell. If you are bringing bulk into the cell, this is known as endocytosis. Endo meaning inside. There are two forms of endocytosis, and let's go over both. In phagocytosis, a solid, a large bulky solid, such as this bacterium, for instance, let's say this purple structure is a large bacterium, the cell membrane will invaginate to form a vesicle around the food, around the bacterium that's being phagocytosed. And that vesicle will internalize, it will pinch off, it'll go pop, it'll pinch off from the plasma membrane, bringing in what's known as a food vacuole. All right. And because you're bringing solids in, in this manner, it's called phagocytosis. However, on the right, check out on the right, in this case, The same concept is happening. Vesicles are forming, bringing substances in, but it's actually water that you are bringing in. Water is bringing brought in as in vesicles. And because the liquid, including anything that's dissolved in the liquid, any solute that's dissolved in the liquid is being internalized. This is known as penocytosis. And so the way you can remember this is. Phage means to eat, and when you eat, you eat solids, whereas pino means to drink, and when you drink, you internalize liquids. So both phagocytosis and pinocytosis are examples of endocytosis. Endocytosis is bulk transport, bulk import of bulky material from outside, and it's a type of active transport because it requires ATP energy or some other form of energy. Now let's move on from nutrients. to environmental factors that can influence microbial growth. Here is a list of various environmental factors that can influence microbial growth. We're going to start with temperature. Temperature is very important for microbes. A microbe's survival is dependent on adapting to the habitat's temperature. With regard to temperature, each organism has a Minimal temperature at which it can grow, a maximum temperature at which it can grow, and an optimum temperature at which it prefers to grow. Below the minimum temperature, that organism typically freezes. It doesn't necessarily die, it freezes. Above the maximum temperature, usually the organism dies because its proteins and its Other components of the cell, they denature and they, you know, come apart. And the optimum temperature. This is the temperature at which the organism performs the best. It grows the best at this temperature here. And different organisms have different cardinal temperatures. So take a look here at ecological groups by temperature. So take a look here. There are some organisms that prefer cold temperatures for growth. In fact, these organisms typically have an optimal growth temperature of around four degrees Celsius and with their minimal temperature being negative 20 degrees Celsius, well below freezing and their maximum temperature around 14 degrees Celsius. These are known as psychrophiles. Let me zoom in here for you. Psychrophiles. Psychrophiles prefer cold conditions for growth. They grow optimally at around 4 degrees C, the same temperature as your refrigerator. Isn't that interesting? So you would find these in colder habitats on the planet. Next, we have these organisms here. These organisms have an optimal temperature of around room temperature, room temperature being between 24, 25 degrees C and with a... minimum temperature of around 4 degrees C and a maximum around 37 degrees C. These are known as psychotolerant organisms. Next, we have the green dashed line here. These are known as the mesophiles. These grow best around body temperature. Look, around 37 degrees C, mesophiles prefer body temperature for growth. And they have a minimal temperature around 10, 11, 12 degrees C and a maximum around almost 50 degrees C. Following that, we have organisms that prefer very warm environments. So for instance, this pink line here, these are thermophiles. Thermophiles prefer to grow in very hot conditions. We're talking around 70 degrees Celsius. This is hot enough to completely denature. your proteins and kill your cells. A mesophile would die in these conditions. And then we're not done yet. There are some organisms that grow in even warmer environments. Look at this brown dash line over here. These are known as the extreme thermophiles. These organisms, they can live in boiling hot conditions. We're talking, you know, the sulfur cauldrons, the sulfur springs. that exist anywhere there are thermal vents where the water is so hot it's boiling these live in these boiling hot conditions and in fact they prefer to exist around 125 degrees c environments you you will find these in thermal vents and such as i mentioned a lot of times these are archaea you know many archaea are extreme thermophiles but also some bacteria Bacteria are extreme thermophiles as well. Now, let me ask you a question. Let me test your understanding. Looking at these different temperature types, which of these five would you suspect would cause the most human diseases, would be the culprit of the most human diseases and be... known human pathogens or most likely to cause an infection in a human. What do you think? Can you beat Wicked? That's right. That's right. Wicked is always mesophiles. Well, think about it. Mesophiles prefer 37 degrees for growth. Your body is at 37 degrees. So, you know, yes, it's most of the human pathogens are mesophiles. Why? Because those pathogens want to grow on your body because they prefer your body's temperature. Moving on to our next environmental condition for growth, gases. Different microbes prefer different gases for growth. Atmospheric gases contain oxygen and CO2. You also have nitrogen in the atmosphere as well. Well, some organisms can grow in the presence of oxygen, and some organisms, they cannot grow in the presence of oxygen. There are three categories of organisms with respect to oxygen. Those organisms that can use oxygen and detoxify it, those that neither use oxygen nor detoxify it, those that do not use oxygen but can detoxify it. So let's delve into this concept of using oxygen and detoxifying oxygen and discuss what this all means. Well, as it turns out, oxygen can be quite tough. toxic to the cell. It can destroy cells, but not in its normal form of oxygen gas, O2. It's when, take a look here, as oxygen enters into cellular reactions, such as metabolic reactions in a cell, it is transformed into several toxic oxygen products. These are known as ROS, or reactive oxygen species. For instance, singlet oxygen, which is a single O, a single oxygen, is extremely reactive. And it's produced by living and non-living processes. This singlet oxygen, if it's present in your cells, it can cause cell damage and cell death because it can cause oxidation of your cellular components. Again. This buildup of singlet oxygen and the oxidation of membrane lipids and other molecules can damage or destroy the cell. Here's another reactive oxygen species. It's called superoxide ion. It's O2 with a negative charge. Here's another one, hydrogen peroxide, H2O2. And here's a third one, hydroxyl radical, OH-. All three of these are examples of ROS. reactive oxygen species which is created by cells during cellular reactions that can cause damage to the cell so much damage that it can kill the cell so when these when these ross molecules build up in a cell they need to be neutralized they need to be dealt with otherwise they could result in cell death so only those organisms that can neutralize these ross can live in the presence of oxygen. I hope that makes sense. So for instance, cells use enzymes that they code for with their genes to scavenge and neutralize these ROS in a two-step process. So for example, step one, the enzyme that's produced by a bacterium or a microorganism, this enzyme superoxide dismutase will convert superoxide radical or superoxide ion 202 minus it'll it'll convert that to hydrogen peroxide right hydrogen peroxide still a form of ross it is a reactive oxygen species however the second enzyme again coded for by a microbial gene the enzyme catalase will then take that hydrogen peroxide and convert it to harmless water so you see Organisms that have these two enzymes, superoxide dismutase as well as catalase, they are capable of neutralizing dangerous ROS, like this superoxide ion as well as hydrogen peroxide. However, an organism that does not possess superoxide dismutase nor catalase, it will have a buildup of superoxide ion or even hydrogen peroxide, and those reactive oxygen species would destroy the cell, again, by attacking the membranes, again, by causing oxidation in the cell, killing the cell. So those organisms that can grow in the presence of oxygen need to create these enzymes or have these enzymes. Those that can't grow in the presence of oxygen tend to lack these enzymes. So with regard to oxygen requirements, aerobes or aerobic organisms are organisms that can use oxygen during metabolism. These organisms do not get destroyed by reactive oxygen species. This is because they produce the enzymes needed to process those oxygen products. Remember superoxide dismutase and catalase. In fact, there are even organisms that are obligate aerobes. An obligate aerobe is an organism that must grow in oxygen. It cannot grow without oxygen. There's another class of organisms called facultative anaerobes. And these organisms, they don't require oxygen for metabolism, but they are capable of growth in the presence or absence of oxygen. These organisms can grow in the presence or absence of oxygen. The way they do that is they undergo aerobic respiration when oxygen is present. And then they switch to fermentation when oxygen is absent. Another class are the microaerophiles. These organisms, they do grow in oxygen, but only low levels of oxygen. So they do not grow at normal atmospheric concentrations of oxygen. The amount of oxygen in the atmosphere is between 20 and 22 percent. And these... organisms do not grow in that range. They prefer lower concentrations of oxygen, for instance, 8 to 10% oxygen. Anaerobes or anaerobic microorganisms, these are organisms that grow in the absence of oxygen. If it's a strict or obligate anaerobe, this means that it lacks the metabolic enzymes. necessary for processing oxygen. So for instance, because strict or obligate anaerobes do not produce the enzymes superoxide dismutase or catalase, they are not capable of processing those reactive oxygen species like singlet oxygen or superoxide ion or hydrogen peroxide. And then they succumb to those reactions. oxygen. So where you find anaerobes, specifically strict or obligate anaerobes, is places that have deep in the mud, lake, ocean, soil, where there's very, very little to no oxygen. And the last class here are the aerotolerant anaerobes. These do not utilize oxygen, but they can grow to a limited extent in its presence. And the reason they can withstand oxygen is because even though they don't use oxygen, they have ways of breaking down peroxides and superoxide radicals. And here we can see bacteria with different oxygen requirements growing inside of broth. Here you can see if the bacteria only grows at the surface. This is an example of a obligate aerob. If it grew just below the surface, just here, but only just below the surface, that would be a microaerophile. If it can grow in the presence or absence of oxygen, then we're talking about a facultative anaerobe or an aerotolerant bacterium. And if it only grows at the bottom of these tubes, then it is a obligate anaerobe, a strict anaerobe. Speaking of gases, some microbes prefer high levels of CO2. These are called capnophiles. Capnophiles grow best at higher CO2 levels than normal atmosphere. Moving on to our next environmental condition, pH. Parts of the earth have different pH environments. There are acidic environments. There are basic environments. There are neutral environments. and each of those environments has organisms that prefer to live in there. Remember that pH is expressed on a scale from 0 to 14, 0 being very acidic, 14 being very basic or alkaline. pH 7 refers to a neutral pH. Organisms that prefer acidic pH for growth are called acidophiles. Obligate acidophiles, as the name suggests, must grow in acidic conditions. Conversely, alkalinophiles prefer alkaline or basic pH environments for growth. Moving on to our next environmental condition, osmotic pressure. These typically refer to hypertonic conditions. Environments with... high solute concentration, for instance, high salt concentration. In fact, osmophiles are organisms that prefer to live in habitats with high solute concentration. Halophiles, as we've discussed before, halophiles, these are organisms that prefer high concentration of salt for growth. Obligate halophiles need high levels of salt for growth, while facultative halophiles, they can grow in the presence of high salt concentration, but they do not need high salt to grow. So for instance, Staphylococcus aureus. It grows on your skin and it's salt tolerant, right? It does not mind that salty environment of the skin. A non-halophile would not be able to grow on the skin. This is why skin infections are often caused by staph. Staphylococcus aureus, Staphylococcus epidermidis. These are bacterium that are halophiles, facultative halophiles. And they prefer to grow on the skin. Other bacteria may not be resistant to the salt levels present on the skin. And so this is why skin infections tend to be caused by staph or another salt-tolerant microorganism. The next environmental factor, radiation. Phototrophs use visible light. Visible light is a type of... electromagnetic radiation. But phototrophs use visible light radiation as an energy source. And there are other forms of electromagnetic radiation that stream onto the earth from the sun as well as visible light. These include ultraviolet or UV light, infrared light as well. Non-photosynthetic microbes tend to be damaged or destroyed by radiation, specifically UV light. UV radiation. Another type of radiation that can damage microbes is ionizing radiation, x-rays or cosmic rays. So some forms of radiation are required for life, such as visible light radiation to photosynthetic organisms. And some forms of radiation are deleterious to life or damage life forms, including ultraviolet or x-ray or cosmic rays as well. Moving on to another environmental factor, hydrostatic pressure. Deep in the ocean, there is high pressure of water. There's high water pressure. And it's the beryl files that can live in this high water pressure, deep sea environment. Moving on to the next environmental factor, moisture. Moisture is required for bacterial and microbial growth. Remember that most of a cell's contents is water. Most of the cell's mass is water. So it's very difficult for microorganisms to grow in a water-free environment. And it's only those dormant dehydrated cell stages, such as spores or cysts, that can tolerate. extreme drying because their enzymes go inactive. Living organisms cannot tolerate extreme drying or desiccation. Now that we've covered the different environmental factors that can affect microbial growth, let's discuss associations between organisms. Namely, we're going to talk about symbiotic associations. We're not going to delve too much into non-symbiotic relationships in this class. Symbiotic relationships are when organisms live in close nutritional relationships. Symbiotic relationships are when two different species coexist. They live together. However, this can be beneficial or this can be harmful. Let me explain. One type of symbiotic relationship is a mutualistic symbiotic relationship. This is the one that people think about when they think about symbiotic relationships. This is when both members benefit. Both of the members are benefiting from one another. This is called a mutualistic symbiotic relationship. However, a commensal symbiotic relationship is when the commensal benefits, the organism that lives on the host benefits, but the other member is not harmed. Now, during parasitism, which is another type of symbiotic relationship, parasites depend and benefit from the host. but the host becomes harmed. The host is harmed, the parasite benefits. And again, students don't usually associate parasitism with symbiosis, but it is a form of symbiosis. So we should know the three different forms of symbiosis. Now one type of association I will talk about are biofilms. Biofilms are mixed communities. Communities refer to different species. of different kinds of bacteria and other microbes all living together and helping each other out. And here's how a biofilm works. Let me give you an example. An example of biofilm would be the plaque on your teeth, right? The plaque that grows on your teeth that you need to brush off at the end of the day. So here's how a plaque forms. Here's how a biofilm forms. First, pioneer bacteria. bacteria colonize a surface. So certain bacteria, for instance, they will adhere to the surface of your tooth enamel. This would be your tooth enamel in the background. And remember, they use adhesion structures such as fimbri or slime layers or even flagella in order to stick to the tooth surface. At this point, what's really cool is that These pioneer organisms will secrete an extracellular material that helps keep them on the surface and serves as an attachment point for later colonizer. They start secreting this goo. And this goo is sugary, proteinaceous goo. And this goo allows other organisms to also attach to this matrix. And at the same time as they're... They're producing this gray goo. They're producing these little red structures. These are called quorum sensing chemicals. Quorum sensing chemicals are chemicals that are released by each of these microorganisms. Each of these bacterium release these quorum sensing molecules. And when a certain concentration of quorum molecules builds up, that triggers a a quorum sensing event. In many, but not all, biofilms, other species join and may contribute to the extracellular matrix, this sugary proteinaceous matrix, and or participate in quorum sensing. Remember, quorum sensing refers to releasing these quorum molecules. Once, again, once a threshold concentration of these quorum molecules has built up, These quorum molecules will reenter these cells and trigger more biofilm formation. So let me explain. Making a biofilm, making a biofilm makes no sense if you're all by yourself, you know, because it's expensive to secrete sugary proteinaceous matrix. You know, this, this goo, uh, it's expensive for the cell to release this goo. If there's one or two cells. They may not want to expend the energy necessary to secrete this goo. And so it's better to save your resources and not secrete the goo if there is no other bacterium around. And how do you know if other bacterium around? That's where the quorum sensing molecule comes in. Each bacteria releases this quorum sensing molecule. Once the quorum sensing molecule builds up to a high enough concentration, Then it triggers the formation of the goo. It triggers the formation of the extracellular matrix, this sugary proteinaceous matrix, which then allows other organisms to help colonize this biofilm. And the biofilm matures. A mature biofilm may stop or minimize quorum sensing. And then at that point, other bacterium can go planktonic again, and they could spread and... go and start another biofilm at this point as well. And by the way, where did quorum sensing get its name? Do you know? In model Congress or in Congress, anytime you have congressional meetings with congressional structure, you have what's known as quorum. This means that a certain percent of the members need to be present in order to start the proceedings. These are called quorum molecules because they ensure that a that a significant number, a satisfactory number of microbes are present in the environment in order to start the process. In this case, it's to create the extracellular matrix, this, this kind of, um, sugary proteinaceous biofilm in that interesting, again, if you're all by yourself. You're not going to reach that threshold concentration of quorum molecule. If you're high enough density, high enough population, then you will have more than enough of this quorum sensing molecule to trigger more biofilm formation. So quorum sensing is a way of bacterium realizing or sensing how many other bacterium are in the environment. The reason for quorum sensing is to make sure or ensure that costly cellular activities, such as making a biofilm, only occur when there are sufficient numbers of microbes in the environment. Isn't that neat? A long time ago, it was assumed that microbes had no way of communicating with one another until quorum sensing was discovered. So quorum sensing, again, it occurs when a bacterium, it makes more sense for them to do that cellular activity as a group than it would alone. So for instance, again, making a biofilm, it makes more sense to secrete that sugary proteinaceous matrix, that biofilm, if you're in a large group and doesn't make sense to waste those resources. If you're all by yourself, another example, making a toxin, some bacterium, they won't make a toxin. against a host unless there's again quorum sensing and a sufficient number of bacterium in the environment another example did you know there are some bacterium that can glow like deep fish bacterium the bacterium that grow deep in the ocean where there is no light okay these bacterium can glow but only when they're in high concentrations in the pockets in the fish you know, in different pockets in the fish membrane and the fish skin. Isn't that interesting? So these organisms will not glow if they're all by themselves, but they will glow due to quorum sensing in a high population. Isn't that neat? Again, bacterium use quorum sensing in order to do cellular activities that makes sense to do in high populations and not alone. Now for the last part of this chapter. Let's talk about population growth, bacterial population growth. Bacteria grow, not by mitosis, but by a process known as binary fission, which is much more straightforward and simple than mitosis. Here's a bacterial cell. You've got this stringy stuff, which is the nucleoid, right? The single circularized chromosome, the nucleoid. Here you have ribosomes as well, those little dots. this is a young cell. This cell will grow. They will elongate. You see how the cell elongates and the nucleoid is copied. Now you have two copies of that single circularized chromosome. Those two copies move to opposite ends of the cell. And then a protein band forms at the center of the cell. This is known as the FITZ band. And then this promotes, uh, cytokinesis. Remember cytokinesis, the separation of the cell itself. And cytokinesis occurs by a process known as septum formation. Septum formation, which is an inward growth of the cell wall of the bacterium. When the septum is complete, the two bacterium are separated from one another. However, sometimes they can remain attached. And this is how staphylo arrangements can form or strepto arrangements might form or diplo arrangements might form if they don't fully separate. Now let's discuss bacterial rate of population growth. How fast do bacteria divide? This is known as the generation time or doubling time of a bacterium. It's the time required for a complete fission cycle. This means one young bacterium growing, elongating, and ultimately becoming two identical copies, right? Dividing into two cells. Hi, Wicket. Wicket has come to say hi. He's on the table right now. Hi, buddy. Wicket. Wicket's come to say hi. Wicket. Always so fun having wickets come say hi. Hi buddy. Hi sweet buddy. What are you up to? Oh gosh he's scratching. He loves to scratch my monitor. So that's what you're hearing right now. We're taking an impromptu break time with Wicket. Wicket's here to say hi. Oh, he's very excited to visit. Hi, buddy. Hi, buddy. Do you hear him purring? I wonder if you can hear him purring through the microphone. Let's listen really close. What are you up to, Wiki? One thing to keep in mind about the generation time is that with each new fission cycle, each generation time. This doubles the population of the bacterium. So long as the environment remains favorable, the doubling effect can continue at a constant rate. Here we can see the cell division doubling time in the population. If we start with a single bacterium, the number of cells is one. The number of generations is zero. And to understand how many... bacterium are present at this point, we take two to the power of the number of generations. In this case, the number of generations is zero. So we have two to the power of zero organisms, and that equals one. There's one organism at time zero, at generation time zero. At generation time one, by the way, many bacteria... bacterium divide between 25 minutes and 35 minutes. So this is very fast for many bacterium. They divide quite quickly. So let's say within 30 minutes, the bacterium would double from one bacterium to two, right? Because that cell underwent binary fission. At this point, you have one generation, one doubling. And the number of cells would be 2 to the power of 1, or 2 total cells. Then, 30 minutes later, those two double. So if both of those double, now you have 4 cells. This is your second generation. To calculate the number of cells, you take the base of 2 to the exponent 2, because there have been two doublings, and 2 to the power of 2 is 4. And we can go on this way. So this is known as a logarithmic growth scale with the base two. These are the number of log base two doublings. And because this is a logarithmic growth, populations can explode in a short amount of time. In fact, for E. coli, for instance, it could take E. coli 25 to 30 minutes to divide. If we start with a single E. coli, it takes five hours or so, give or take, to make a million E. coli. So from one bacterium, one E. coli, it would take about five hours to make a million. And I always ask myself, I always ask my students, let's see if you can beat Wicket. If it takes one E. coli, five hours to... result in a million E. coli, right, to divide and become a million population, then how long would it take for another million, for two million to form? Can you beat Wicket? All right, Wicket, good job. Another 20 minutes. So it took five hours to get your first million E. coli. But it would only take another 20 minutes to get your next million. Remember, it's exponential growth. Every doubling time, you are doubling the population. So yes, Wicked is right. It would only take another 20 to 25 minutes to result in 2 million E. coli. This is because the doubling time of E. coli is roughly 25 minutes. Isn't that neat? So this is why... when we plate ourselves on media, you know, if you make like a spread play or a streak play. Then you put those plates in the incubator and we come back, remember, two days later, three, four days later, you know, and we take a look at those plates. What do we see on those plates? We see a bunch of bacterial growth. And each one of those colonies represents millions upon millions upon millions of, you know, E. coli or whatever species you're studying. And the reason why you see those colonies is because a single cell. divided exponentially right with a base of two they doubled every 20 25 30 35 minutes depending on the species and that resulted in a colony by the time you returned so a single cell became millions upon millions if not billions in a few short days this is also why we refrigerate our food for instance You know what happens when you take food out of the refrigerator? Any microbes that happen to be on that food start to divide, right? Because they were not dividing so fast in the refrigerator, but you remove that food from the refrigerator and those microorganisms start to divide. And remember, they divide exponentially. So there might be just a few E. coli on your, you know, potato salad when you removed it from the... from the refrigerator, but you left it on the counter. Well, guess what? After five hours on the counter, each one of those E. coli is now a million, right? And if you leave it for another 20 minutes, each one of those E. coli is now 2 million. And now if you were to eat that warm food that's been sitting out, you know, now you would get food poisoning. You would come down with an illness, right? However, if you had refrigerated that food, then those bacterium would not have divided so fast. Your food would not have spoiled and you would have been fine eating that same potato salad if it had been properly refrigerated. So now we know the importance of refrigerating our food, right? And it's all based on this chapter. This chapter is so interesting. It explains why we refrigerate our food. Why? Because many organisms that cause human diseases are these organisms that are mesophiles. Remember, mesophiles grow best at human body temperature. If we're keeping our food in the refrigerator at four degrees C, then that's below the minimum growth temperature of many mesophiles. So those microorganisms can't grow. And if they can't grow, they don't form sufficient concentrations to cause human disease or food poisoning. But if you remove the food from the refrigerator, those microorganisms begin to animate. They begin to grow and divide exponentially with logarithmic growth. And next thing you know, you have food poisoning. So isn't that interesting? Also, All the other environmental conditions play a role as well. So for instance, remember, not all microorganisms can grow in high salt. So this might be why we salt our foods, to preserve them. Have you heard that salt is a preservative, a very important preservative? And by salting our foods, we can preserve them and prevent bacterial growth and for the food to become spoiled? bacterium are halophiles. Only halophiles can grow in high salt. And so by doing that, we reduce the number of microbes that grow on the food. Also dehydrating. Why does steak go bad so easily if it's left at room temperature, but not beef jerky? Beef jerky is just dried out steak. So remember, many organisms, all organisms require moisture to grow. Beef jerky is too dry to grow on, right? There's not enough moisture for the microbe to grow on that surface. Isn't that interesting? Also, why do we pickle our foods? You know, when you pickle a food, it makes it more preserved. It keeps its shelf life much higher. You know, pickles last a lot longer than cucumbers, don't they? Well, why is that? Well, because it's an acidic pH. It's an acidic environment. And again, only acidophiles would want to grow in that environment. Isn't that really neat how this chapter kind of plays into how we treat food? And it should also play into how we treat, you know, the clinic in the medical setting in order to help keep the health of our patients in order to prevent the spread of disease. The better you understand microorganisms and their growth requirements, as is the topic of this chapter. the better you can treat for your patients, but also the better you can stay healthy at home and with your own food, you know, in your own kitchen. Isn't that neat? Okay, again, if we plot bacterial growth on a log scale, then it is a linear logarithmic growth of bacterium over time. However, if we do not use a log scale, it appears like the bacterium grow asymptotically. They grow exponentially, but they form kind of this asymptote as they grow. So normally when we're talking about bacterial growth, we depict it on a logarithmic scale so that you see this nice straight line here. And for the last concept from this chapter, let's talk about a population growth curve. A growth curve is a predictable pattern of growth in a population of bacteria. Specifically, let's look at a growth curve in bacterial culture. This is also known as batch culture. If you have, let's say, a limited environment with limited resources, limited nutrients, and limited space. So, for example, what if I have nutrient like TSB broth inside of a test tube? Do you agree that there's limited nutrients in this broth? Limited space in this broth? Well, that's what bacterial culture means. There's limited resources. So like imagine a flask of broth or a test tube of broth. Well, when we have a test tube of broth and we seed it with some E. coli, we seed it with some bacteria, there are one, two, three, four very predictable growth curves that occur. And this is how it works. On the y-axis, we have the log scale of viable cells. So we have the log scale of cells. These are living cells. And on the x-axis, we have hours, number of hours. So when I place E. coli, this many E. coli into broth, at first, there's always what's known as a lag phase. During the lag phase, this is a flat. period on the graph when the population appears not to be growing. This is because newly inoculated cells, remember I said I just added some E. coli to this environment, I recently inoculated the environment with E. coli, these require a period of adjustment, enlargement, and synthesis. Cells just can't multiply at their maximum rate. So here, during the lag phase, the bacterium are becoming active. acclimated to their environment. Then at some point, now that they're acclimated to their new environment, they enter what's known as the exponential growth phase. Remember, this is the log growth phase where the bacterium double and double and double and double every generation time, every doubling time. However, at some point, we enter the third phase of the bacterial growth curve phase. Here we see it's called the stationary phase. At this point, the party's kind of over. We've exhausted all the nutrients and the space, and the bacterium can no longer grow. So at this point, we enter stationary phase in which no doubling is occurring. No bacterial doubling is occurring. And then after a period of time, we enter our final phase, the death phase. Because these bacterium have... been stewing in their own waste, you know, because there's waste in here. There's no nutrients in here. They become sick and a number of cells die off. And this is known as the death phase, sometimes known as the senescence phase. And that's it for this chapter. We talked about all of the nutritional and growth requirements for bacterial cells and microbes. I hope this chapter was informative. It was really interesting reflecting back on. how we treat our food and how it has everything to do with the bacterial, nutritional and environmental growth requirements. So I think that's neat. I hope you found it neat as well. Please let me know if you have any comments in the comment box below, and I will catch you guys next time. Dr.

So, just like you and me, we need nutrients in order to grow. Microbes are no different. They need a source of nutrients in order to grow and develop and to divide. And so this chapter talks about the different microorganisms and where they obtain their nutrition from. So, first of all, what...

is nutrition. Nutrition requires nutrients. Nutrients are acquired from the environment and used for cellular activities.

These activities, like I said, include growth and division. Organisms require a constant influx of certain substances from their habitat to fulfill their dietary needs. And the source of the particular elements, their chemical forms, and how much of the element is needed varies among different types of organisms.

We're going to be talking about the different elements, the different molecules, the different nutrients that these organisms need in order to grow. And here you can see a list of different elements from the periodic table of elements. We have different elements that...

are required by all living organisms, carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulfur, and so on and so forth. There are also a host of other elements that we need in trace amounts, in minute amounts as well. So we're going to talk about these different elements. We're going to talk about which ones of these elements make up our biomolecules. you know, where we source these from and where microorganisms source these elements from.

So again, we have certain nutrients that all organisms require. Essential nutrients are substances that must be provided to an organism. For instance, all organisms require carbon, hydrogen, oxygen, nitrogen.

phosphorus, and sulfur. All organisms require these handful of elements because these are the central elements to our major biomolecules. And I'll show you what the biomolecules are in a little bit.

Macronutrients refer to the nutrients that are required in relatively large quantities. So for instance, carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur are all macronutrients. macronutrients. Micronutrients, on the other hand, also known as trace elements, are required in small amounts or minute amounts.

So for instance, you know, you require copper, zinc, you require iron in your diet. These would be trace elements required. And a lot of times, these trace elements, they serve as cofactors.

They are involved in enzyme function and maintenance of protein structure. So for instance, remember what a cofactor is? A cofactor is an enzyme helper or a protein helper. A cofactor binds to an enzyme or a protein to allow it to function correctly.

So for instance, hemoglobin in your blood requires the cofactor iron in order to properly transport oxygen. Inorganic nutrients, as their name suggests, are nutrients that lack carbon. Organic nutrients, these are nutrients that contain carbon plus hydrogen.

Common inorganic nutrients are elements like iron, zinc, sulfur, potassium. Common organic nutrients include things like vitamins or growth factors. Here we can see some of the principal inorganic elements and their reservoirs.

The reservoirs mean where they obtain their elements from. So organisms can obtain their carbon either from the air in the form of CO2 or from rocks and sediments. Organisms can obtain their oxygen either from the air, certain oxides, and water.

So I'm not going to go through this entire list, but it gives you an idea of where microorganisms can obtain their elements, the reservoirs that... harbor these elements and where they can obtain these elements. Now, what is the chemical composition of a bacterial cell? Because by looking at what a bacterial cell is comprised of, we can glean, we can understand from that the nutritional requirements of that bacterial cell. Well, it turns out about 70% of the cell content is water.

And that makes sense. Most of your body weight is water as well. And then the proteins are the next most prevalent chemical. So when we subtract the water weight of a cell, the remainder is known as the dry cell weight. Imagine taking a bacterial cell and completely dehydrating it, removing all water.

Well, you would remove 70% of the bacterial cell's weight. But what's left over is the dry cell weight. And 97% of the dry cell weight is composed of organic compounds. This means the molecules that have carbon and hydrogen as well. Now, 96% of the dry weight is composed of only six elements.

Remember these six elements? I called them chomps, right? Um, carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.

These, these six elements alone make up 96% of the dry weight of the cell. And that's why these are definitely macronutrients, nutrients that are required in relatively large amounts by the cell. Again, proteins make up only 50% of the dry weight of the cell. 15% of the total weight of a bacterial cell such as Escherichia coli, but it makes up 50% of the dry weight of the cell.

RNA makes up 20% of the dry weight. DNA makes up 3% of the dry weight of the cell. Carbohydrates make up 10. Lipids make up 10. And then miscellaneous make up the remainder 4. These are the organic compounds. So by the way, these major organic compounds are known as biomolecules. Proteins, RNA and DNA.

By the way, the RNA and the DNA are known as nucleic acids. Then you have the carbohydrates and the lipids. These are biomolecules.

And the biomolecules make up the majority of the dry weight of the cell. What about inorganic molecules? Inorganic molecules only make up about 1% of the total cell's weight, while water, remember, makes up 70% of the cell's weight.

Water is abundant in all living cells. Again, we can have a breakdown on the right here of various elements and their contribution to the dry weight of the cell. Remember, the macronutrients, the macronutrients, are required in relatively large amounts in the cell, while the micronutrients are required in lower quantities in the cell.

A major way that organisms are categorized based on their nutritional requirements has to do with where they obtain their carbon. This is known as their carbon source. Consumers like you and me are known as heterotrophs because we obtain our carbon from organic compounds that we ingest. Just think about it.

Where do you think you get your carbon from? Remember, we need a large source of carbon in our nutrition, in our diet, because carbon is the most abundant element in our dry mass of our cells. So where do we get our carbon from?

Well, don't we eat breakfast, lunch, and dinner? We obtain our carbon from our diet, from things we eat, organic molecules that we consume. So these organisms that get their carbon from organic molecules they consume are called heterotrophs.

So you and I, we are heterotrophs. We obtain our carbon from organic molecules. And this means that we are dependent on other life forms. We cannot feed ourselves.

We need to consume other organisms to obtain carbon molecules. Conversely, autotrophs are organisms that obtain their carbon from CO2 from the air. There is CO2 floating around in the air.

And autotrophs can actually capture inorganic CO2 as their carbon source. That's where they get their carbon from. It's a process known as carbon fixation. If any of you have studied photosynthesis in the past, you know that CO2 is a carbon source. that during the Calvin cycle, CO2 is captured from the air and that's known as carbon fixation.

So can you and I, let's see if you can beat Wicket. Can you and I undergo carbon fixation? Can we take CO2 out of the air as our source of carbon? That's right, Wicket.

Wicket is so smart. We cannot, right? Because, you know, this is what plants do.

Plants have chloroplasts. They've got the ability to capture CO2, right? And photosynthetic organisms can capture CO2 from the air.

They are autotrophs. And because they can capture CO2 from the air and they don't require other organisms, they don't have to eat other organisms. They're known as self-feeders.

These are the producers in the environment, in ecology. When we're talking about the ecosystem, the autotrophs are the self-feeders. They don't have to consume other organisms to live.

And because of that, they tend to be producers. They are at the bottom of the food chain. They're the source of the organic molecules for the rest of us, us heterotrophs. And once they obtain that CO2, they can convert that CO2 into other carbon compounds like sugars or different biomolecules. Without these autotrophs, we would have nothing to eat.

The food web would collapse. The ecosystem would have no way of sustaining itself and it would collapse. The autotrophs are at the bottom of every food web and they are the producers in the ecosystem. So without autotrophs, there would be nothing for heterotrophs to consume and we would perish as heterotrophs. Now, moving on to nitrogen sources.

Remember, nitrogen is another macro element that microorganisms need in large amounts. Nitrogen can be sourced from the air. Some organisms, these are known as nitrogen fixers. Some organisms can actually take nitrogen from the air, and that's a good resource. And the air is actually a great source of nitrogen, seeing as how 79% of the atmosphere is basically made up of nitrogen.

So some organisms can actually capture nitrogen from the air, and these are known as nitrogen fixers. Now, you and me, we obtain our nitrogen from our diet. We consume other organisms, so we're eating their proteins, their DNA, their RNA, their ATP, and that's where we source our nitrogen.

And now, what about microorganisms such as E. coli? Where do they get their nitrogen from? Well, some bacteria and algae utilize inorganic nitrogenous nutrients such as NO3 minus, this is nitrate. NO2 minus, this is nitrite.

Or NH3, this is ammonia. These are three common sources of nitrogen for microorganisms. So if you can't fix nitrogen from the air, you can always gain it from your environment in the form of these three molecules, these three inorganic molecules. Next, what about... oxygen sources.

Where do we get oxygen from? Well, first of all, oxygen makes up 20% of the atmosphere. So that's one source of oxygen, but also from your diet or from the environment as well.

How about hydrogen sources? Well, we can get hydrogen from our diet, from biomolecules that we consume. Plants get their hydrogen from water.

They can actually remove hydrogen atoms from water molecules. And hydrogen is important in oxidation reduction reactions in the cell, such as photosynthesis and cellular respiration. Without hydrogen, without access to easy hydrogen elements, photosynthesis and cellular respiration would not. be possible.

What about a phosphate source or phosphorus source? Where do we get those? You and I obviously get our phosphorus from our diet, the molecules we eat, but there are other inorganic sources of phosphate. So for instance, in mineral deposits from soil and such, microorganisms can obtain their phosphate from their environment in the form of these If these deposits and what about sulfur?

Remember, sulfur is a macronutrient as well. Well, it's widely distributed throughout the environment, rocks and sediments. So it's it's easy to find it in the environment.

It is an essential component of vitamins such as vitamin B1, and it's required in two of the 20 amino acids, methionine and cysteine. What about essential organic nutrients? Remember I said organic nutrients include the vitamins and the growth factors.

So these organic nutrients such as amino acids, nitrogenous bases, vitamins that cannot be synthesized by an organism, they must be provided by the environment. Now another way that organisms are categorized based on their nutritional types is how they get there. energy.

Organisms that get their energy from sunlight are known as phototrophs, while organisms that obtain their energy in the form of chemical compounds, either organic chemicals or inorganic chemicals that they consume, these are known as chemotrophs. So let me ask Wicket, let's see if you can beat Wicket. Which one are we? Are we phototrophs or chemotrophs? That's right, as always, Wicket.

We are chemotrophs. We are organisms that obtain our energy from chemical compounds that we consume. And so heterotrophs tend to be chemotrophs for the most part.

We are chemotrophs. We obtain our energy from chemical compounds that we consume. Photo trophies, on the other hand, these would be your photosynthesizers. These would be organisms like cyanobacteria, algae, plants, trees, photosynthetic organisms. These are the organisms that obtain their energy from sunlight.

So let's bring these concepts together then. What do you think a photo autotroph is? Well, remember, let's break down this term.

Photo means... an organism that obtains its energy from sunlight. And auto means an organism that obtains its carbon from CO2.

So a photoautotroph would be something like a plant or a cyanobacteria or algae, an organism that obtains its energy from sunlight and its carbon from CO2. What about a chemoheterotroph? A chemoheterotroph, remember chemo, means an organism that obtains energy from molecules that it consumes.

And heterotroph means that it's an organism that obtains its carbon in the form of organic molecules. So a chemo-heterotroph gets its energy from molecules that it consumes, and a heterotroph is an organism that contains its carbon in the form of molecules. form of organic molecules. Did you know that there are organisms that can mix things up a little bit?

So for instance, a chemoautotroph, a chemoautotroph would be an organism that gets its energy from molecules that it consumes. But autotroph refers to an organism that gets its carbon from CO2. There are microorganisms that can do this. There are chemo-organic autotrophs and chemo-litho autotrophs as well.

Chemo-organic autotrophs use organic compounds for energy, but inorganic compounds as a carbon source, while chemo-litho autotrophs require neither sunlight nor organic nutrients and rely totally on inorganic materials. How can they do that? They can remove electrons from inorganic substrates such as hydrogen gas, hydrogen sulfide, sulfur, or iron.

So the point of this slide is to show you that there's quite a diversity in nutritional types. So just because you're familiar with plants and animals, that doesn't mean that all organisms, especially microorganisms, behave in the same way. There are Organisms that are quite diverse in their nutritional requirements, they can get their nutrition in very distinct and different ways.

Energy cannot be used in the form of sunlight or these chemicals like sugars and fats. So organisms undergo a process known as cellular respiration, oftentimes aerobic. cellular respiration.

You may have learned about this in Biology 1406. This is the process by which glucose and oxygen become CO2, water, and ATP energy. Microorganisms use oxygen in this process and some microorganisms can use a molecule other than oxygen in this process as well. Either way, this is the process by which many animals, protozoa, fungi, and bacteria obtain their ATP. And remember, ATP is the energy currency of the cell. Now, when an organism is considered a saprobe or a saprobic organism, these are known as the decomposers.

These organisms can decompose plant litter, animal matter, dead microbes, anything that's dead organic matter. These organisms are important for recycling nutrients in the environment, in the ecosystem. Usually when we're talking about saprobes, these decomposers, we're referring to bacteria and fungi.

Fungi are probably the best known saprobe organisms. The way these organisms work... is that they cannot engulf the large organic molecules.

Instead, they release enzymes that break down that organic matter, and then they transport the broken down organic matter into the cell. Here you can see what I'm talking about. This is a bacterial cell or a fungal cell. This is a saprobe right here in green. This is a decomposer.

This out here represents... The organic debris, large organic debris. Now, again, the bacteria will feed on this debris, but the bacteria can't internalize these large pieces of debris. So what the organism does is it releases these hydrolytic enzymes, enzymes that are capable of breaking down organic matter, and then transport these broken down nutrients into the cell. So you see.

You can then absorb those raw components, those sugars, those fats, those nucleic acids, those amino acids, etc. into the cell. And this is how decomposers work. Many of these decomposers are obligate saprobes, which means they must feed off of dead organic material. However, some of these organisms can be facultative parasites. which means that they are capable of feeding off a host.

Think of a fungal infection, right? There are human fungal infections. In that case, the fungus is a parasite on you, the host. That's what a parasite does. A parasite becomes dependent on the host for its nutrition.

So when I say parasite, think of something that becomes dependent on the host on which it lives for its nutrition. parasites, again, they live on or in the body. They can cause some degree of harm. Different parasites can cause different degrees of harm.

Some parasites, you may not even know they're there like a tapeworm, but it still causes harm because it depletes nutrients from the host. And you know, it also inserts its hooks into the gut lining, which can cause an infection. So, you know, a tapeworm is one of the more mild. parasites but then there are parasites that cause a lot of damage a lot of disease and can cause death even hi gizmo hey gizmo has come to visit you guys i got him gizmo say hi oh no that's wicked Wicket has come to say hi, people. Yay!

Everyone loves a Wicket. Hi, Wicket. Thank you for visiting, buddy.

Okay. All right. He's going off to bed, I think. Awesome. Well, we always enjoy visits from Wicket.

I thought it was Gizmo, but Gizmo's in his bed right here. Parasites are considered pathogens because they can cause damage to host. tissues and can sometimes even cause death to the host.

These parasites can range from viruses to worms. So there are many different organisms and small infectious agents which are considered parasites. An obligate parasite is unable to grow outside of the living host.

And an obligate intracellular parasite is a parasite that must spend at least part of its life inside of a host cell. That's what intracellular means, by the way, inside of the cell. So if it's an intracellular parasite, this parasite lives and feeds inside of your cells, whereas other parasites might live among your cells or on your tissues. Now, most microorganisms especially single cell ones, they lack a mouth, right?

Like you and I have a mouth and a digestive tract. So how did these bacteria, for instance, how do they get their nutrition? Well, it's called nutrient absorption. The necessary nutrients must be taken into the cell and then waste materials must be transported out of the cell. So this requires what's called transport.

Things need to be transported into the cell and out of the cell through the cell membrane. To understand how substances get into the cell or out of the cell through the plasma membrane, we need to remember this concept of diffusion. Diffusion is a spontaneous process. It does not require energy.

In fact, diffusion releases energy. Diffusion is simply the movement of molecules in a gradient from an area of high density or concentration to an area of low density or concentration. So if I, for instance, if I release a gas right here, that gas will spontaneously diffuse through the room. It will go from an area of high concentration where I release the gas to an area of low concentration. you know, the rest of the room.

And that's a spontaneous process. It does not require any energy to occur. If you remember from earlier biology classes, this would be known as a spontaneous or negative delta G reaction. Spontaneous reactions do not require energy. And diffusion is an example of something that does not require energy.

It's a spontaneous process. So for a substance to diffuse across the cell. membrane or plasma membrane, this, if it's happening by diffusion, then it does not require energy.

Next, let's discuss osmosis. Osmosis is simply the diffusion of water across a membrane, a selectively permeable membrane. That's all osmosis means.

Remember that a membrane is select or differentially permeable. This means that not just anything can enter the cell and not just anything can float out of the cell. The cell can determine what can enter the cell or what can exit the cell. Remember from earlier biology classes, if you had them, that when a membrane is placed between solutions of different concentrations, and the solute is larger than the pores, then water will diffuse at a faster rate from the side that has more water to the side that has less water until equilibrium is reached. So let me explain how osmosis works.

Osmosis is diffusion of water across a selectively permeable membrane. So now let's take a look at this example from your book. Here we have solute. And remember, solute is the substance that's dissolved in the water.

And then you have the solvent, which does the dissolving. This is the water. Here you can see an example where we have a semi-permeable membrane. Outside in the environment, we have pure water. And inside of that membrane, we have water.

plus the solute sugar. Let's pretend these dots represent sugar. These red dots represent sugar.

If we take a close look at the membrane, it is a selectively permeable membrane because it is permeable to water. However, it is not permeable to the sugar. This means that the sugar cannot cross the membrane, but the water can. Now let me ask you this and let me see if you can beat Wicket.

Which way, if the water is the only component that can move across the membrane, not the solute, which way will the water travel from the environment into the cell or from the cell into the environment? Let's see if you can beat Wicket. That's right. Hopefully you got it correct, just like Wicket. And that means, yes, the water flows into the cell.

The water is more concentrated out in the environment. The water is less concentrated in this cell. And so the water will travel from where water is more concentrated to where water is less concentrated.

Whatever is moving across the membrane, whatever is diffusing will diffuse from where it is high in concentration to where it is low in concentration. If these pores were larger. then the sugar, the red dots, would diffuse out of the cell.

They would go from in to out because the sugar is more concentrated inside than outside. But remember, the sugar cannot cross the membrane because the pores are too fine. The membrane is selectively permeable. And so the water is what's mainly crossing the membrane. If that's true, the water will move from where water is more concentrated to where the water is more concentrated.

to where water is less concentrated. And yes, if you're curious, whichever way the solute would like to go, whichever way the solute would like to diffuse, the water always wants to diffuse the opposite direction. So yes, whichever way one wants to go, the other one always wants to go the other direction. Remember, just like this example here, the cell itself has a number of solutes inside.

versus its environment. Sometimes the microorganism can find itself in an environment that has less solute concentration than inside. And sometimes the organism can find itself in an environment with more solute concentration than inside.

And sometimes the organism is in an environment with the equal amount or equal concentration of solute inside and outside of the cell. These are known as tonicity environments. Tonicity problems are osmosis problems. It's water which is crossing the membrane into the cell, out of the cell, or having no net flow in or out of the cell. I have a nice short video I would like you to watch.

I'm going to throw up a card. Uh, here, I'm going to throw up a card here and that will direct you to my review on tonicity. And it's a thorough tonicity review.

I assume that most of you who have taken this class have also taken biology 1406, where we talked deeply about tonicity and how the environment can affect a cell. If not, please go ahead and watch that video so that you are brought. up to speed and then meet me back here so that we can review how tonicity affects microorganisms. I'll wait for you here.

In fact, this might be a good break time with Gizmo and Wicket. That way you could go watch that video and I can hang out with my cats. All right, we'll reconvene in just a minute. Welcome back from break time with Gizmo and Wicket. Let's get back into this review of tonicity problems.

Hopefully my short review video helped you and you remember the concepts of diffusion, osmosis, dialysis. You understand. isotonic, hypotonic, and hypertonic conditions. That's great. So let's do a quick review right here.

In an isotonic solution, that's this example on the left, if we're dealing with a type of cell wall-less cell, this is a cell without a cell wall, such as an amoeba or a paramecium. In an isotonic environment, there's equal concentration of solute inside of the cell as outside of the cell. The solute is depicted here in green.

And the solvent is water. You can't really see the water, but you can imagine it's surrounded by water. In this case, remember, for every one water molecule that enters the cell, about one water molecule leaves the cell.

So there's no net flow of water. In this case, the cell will neither gain nor lose net water volume. Here, this is a bacterial cell.

Remember back... Bacterial cells typically have a cell wall here depicted in pink, a cell wall of peptidoglycan. And that cell wall is in addition to the plasma membrane, it's strengthening the cell.

In this case, again, there's an equal solute concentration outside as inside. Again, it's an isotonic solution. So water should not net flow into the cell, nor should water net flow out of the cell.

We are at equilibrium. Either way, the cells are intact. The cells are healthy. Now let's discuss what happens in a hypotonic solution.

This means a solution with a lower solute concentration in the environment. Hypo means low. Hypotonic solution means a low solute solution. In this case, you have a lot.

more solute. So you see the green dots here. For instance, I'll give you an example like salt. Let's say these green dots represent the solute salt.

And you see how there's a higher salt concentration inside of the cell versus outside of the cell. This is known as a hypotonic environment. In this case, water, remember, solute cannot leave the cell. Solute cannot enter the cell. These are tonicity problems, which means they are osmosis problems.

So only water can flow. The solute can't leave the cell. So water will enter the cell. Water will flow from where water is more concentrated outside of the cell to where water is less concentrated inside of the cell. And if you don't have a cell wall to protect you from, you know, this volume increase, then that osmotic stress will lyse the cell.

The cell will actually break apart and get destroyed. Lysis means to break. The cell will lyse. However, a bacterial cell in a hypotonic solution will fare differently because when water flows into the cell, the cell will swell up.

However, it won't pop. Do you know why it won't pop? Let's see if you can beat Wicket to the answer. Hey, Wicket.

Why does this cell not pop? Exactly right, Wicket. It's that tough cell wall, that ptidoglycan cell wall.

That cell wall is so firm that it prevents lysis of the bacterial cell. Same thing in plants. You know, in plants, plants can also withstand hypotonic solutions or environments because plants have a cell wall of cellulose and that prevents them from exploding. By the way, you want to know a fun fact? Do you know how penicillin works?

You know how penicillin is a potent antibiotic against certain bacteria? Well, the way penicillin works is that it compromises the cell wall. You see this cell wall in pink? Well, that cell wall is compromised by penicillin. Penicillin prevents the cell from maintaining its cell wall.

And then guess what happens if a bacteria... bacterium can't maintain that cell wall of peptidoglycan, it's compromised, and then the cell will lyse. Isn't that interesting?

So that's how penicillin works. Now our last example here, a hypertonic solution. Remember, this is an environment that has a high solute concentration compared to the cell.

So here you can see there's a lot more salt, a lot more solute outside of the cell in the environment than inside. In this case, again, the water will flow from where water is more concentrated inside of the cell to where water is less concentrated outside of the cell. And that results in the cell shriveling up like a raisin. And this is known as a shriveled.

cell or also known as a crenated cell now cells that have a cell wall they also shrivel but it's not the cell wall that shrivels notice how the cell wall did not change much it might be less bloated right the cell wall does not shrivel however the plasma membrane see here the plasma membrane in yellow the plasma membrane which should be pressed against the cell wall, is now peeling away from the cell wall. See how the plasma membrane has peeled away from the pink cell wall? And so it's the plasma membrane that's shriveling up because of the water loss. Water is net diffusing out of the cell.

This makes the plasma membrane peel away from the cell wall, resulting in what's known as a plasmalized cell. This is a plasmalized cell. A plasmalized cell is a cell where the cell wall is intact, but the plasma membrane has peeled away due to efflux of water in that hypertonic environment. Now recall that diffusion is a spontaneous process.

Diffusion occurs without energy input. It is a negative delta G reaction. It's exergonic. And so anytime you see the term diffusion, you should think that no energy is required for that process to happen. If a substance diffuses across the membrane itself, this is known as simple diffusion.

And this is a type of transport. because you're transporting a substance across the membrane. And this is known as a type of passive transport. Passive meaning no energy is required.

So simple diffusion of a substance would be if a substance diffused across the membrane, directly across a membrane. And this is an example of passive transport because no energy was required to transport that substance into the cell. So for instance, if oxygen diffuses into a cell, that's passive transport. That's simple diffusion.

If CO2 diffuses out of a cell, that's simple diffusion. Again, a type of passive transport. No transport protein is required for simple diffusion, passive transport across a cell. However, if a molecule is... polar or charged, polar meaning it has partial negative ends or partial positive ends, or charged as in ions like sodium cation or chloride anion.

In that case, for it to diffuse and transport across the membrane, it requires a transport protein. So let's pretend that this molecule here, this molecule in purple, let's pretend that's glucose. or water, which is a polar molecule, or let's pretend it's sodium cation or chloride anion.

These substances cannot simply diffuse across a membrane because of the polar, the non-polar region here. These tails are non-polar. That means that polar and charged substances need to travel through transporters to get into the cell. Because a transporter is required for this type of diffusion, this type of transport, those proteins are facilitating the diffusion, and this is known as facilitated diffusion. Facilitated diffusion.

Facilitated diffusion, unlike simple diffusion, requires a transport protein to allow the polar or charged ion across the membrane. Again, though, it's a type of diffusion, so that means no energy is required. So it is also an example of passive transport.

Now, if you want to move a substance against the concentration gradient from low concentration to high across the membrane, this is known as active transport, and it's going to require energy. Energy is required. Energy is required for active transport.

transport. Moving a substance from low concentration to high, that means you're going against diffusion and that would require energy. That would not be spontaneous.

Here we can see an example of active transport. Imagine if these thumbtack looking things are some molecule and you're trying to expel that molecule where there's already a high concentration of these molecules outside of the cell. There's a lower concentration of these molecules inside of the cell and you're transporting these molecules out to where they're already high in concentration. Again, this would be an example of active transport, and it would not occur without ATP energy or some other form of energy.

In this case, you can use that energy in order to move a substance against the concentration gradient. That means against the force of diffusion. Now, this other concept of group translocation, we're not going to delve too much into it, but it simply means that when a substance is transported across the membrane by a facilitator, by a transport protein, it's modified along the way. Notice how these pink substances, they picked up a green square on the way in.

That means that the substance was modified upon transport across the membrane. Well, that's what group translocation means. And usually this modification is a phosphorylation, like this. pink molecule picked up a phosphate group, for instance, but it could be other things as well. Now, for the last type of transport that we're going to talk about, this is another form of active transport, but it's called bulk transport.

Bulk transport, because you are bringing bulky items into the cell, or you are expelling bulky items out of the cell. If you are bringing bulk into the cell, this is known as endocytosis. Endo meaning inside.

There are two forms of endocytosis, and let's go over both. In phagocytosis, a solid, a large bulky solid, such as this bacterium, for instance, let's say this purple structure is a large bacterium, the cell membrane will invaginate to form a vesicle around the food, around the bacterium that's being phagocytosed. And that vesicle will internalize, it will pinch off, it'll go pop, it'll pinch off from the plasma membrane, bringing in what's known as a food vacuole.

All right. And because you're bringing solids in, in this manner, it's called phagocytosis. However, on the right, check out on the right, in this case, The same concept is happening.

Vesicles are forming, bringing substances in, but it's actually water that you are bringing in. Water is bringing brought in as in vesicles. And because the liquid, including anything that's dissolved in the liquid, any solute that's dissolved in the liquid is being internalized. This is known as penocytosis. And so the way you can remember this is.

Phage means to eat, and when you eat, you eat solids, whereas pino means to drink, and when you drink, you internalize liquids. So both phagocytosis and pinocytosis are examples of endocytosis. Endocytosis is bulk transport, bulk import of bulky material from outside, and it's a type of active transport because it requires ATP energy or some other form of energy. Now let's move on from nutrients. to environmental factors that can influence microbial growth.

Here is a list of various environmental factors that can influence microbial growth. We're going to start with temperature. Temperature is very important for microbes.

A microbe's survival is dependent on adapting to the habitat's temperature. With regard to temperature, each organism has a Minimal temperature at which it can grow, a maximum temperature at which it can grow, and an optimum temperature at which it prefers to grow. Below the minimum temperature, that organism typically freezes. It doesn't necessarily die, it freezes. Above the maximum temperature, usually the organism dies because its proteins and its Other components of the cell, they denature and they, you know, come apart.

And the optimum temperature. This is the temperature at which the organism performs the best. It grows the best at this temperature here.

And different organisms have different cardinal temperatures. So take a look here at ecological groups by temperature. So take a look here. There are some organisms that prefer cold temperatures for growth. In fact, these organisms typically have an optimal growth temperature of around four degrees Celsius and with their minimal temperature being negative 20 degrees Celsius, well below freezing and their maximum temperature around 14 degrees Celsius.

These are known as psychrophiles. Let me zoom in here for you. Psychrophiles.

Psychrophiles prefer cold conditions for growth. They grow optimally at around 4 degrees C, the same temperature as your refrigerator. Isn't that interesting?

So you would find these in colder habitats on the planet. Next, we have these organisms here. These organisms have an optimal temperature of around room temperature, room temperature being between 24, 25 degrees C and with a... minimum temperature of around 4 degrees C and a maximum around 37 degrees C. These are known as psychotolerant organisms.

Next, we have the green dashed line here. These are known as the mesophiles. These grow best around body temperature. Look, around 37 degrees C, mesophiles prefer body temperature for growth. And they have a minimal temperature around 10, 11, 12 degrees C and a maximum around almost 50 degrees C.

Following that, we have organisms that prefer very warm environments. So for instance, this pink line here, these are thermophiles. Thermophiles prefer to grow in very hot conditions.

We're talking around 70 degrees Celsius. This is hot enough to completely denature. your proteins and kill your cells. A mesophile would die in these conditions.

And then we're not done yet. There are some organisms that grow in even warmer environments. Look at this brown dash line over here.

These are known as the extreme thermophiles. These organisms, they can live in boiling hot conditions. We're talking, you know, the sulfur cauldrons, the sulfur springs. that exist anywhere there are thermal vents where the water is so hot it's boiling these live in these boiling hot conditions and in fact they prefer to exist around 125 degrees c environments you you will find these in thermal vents and such as i mentioned a lot of times these are archaea you know many archaea are extreme thermophiles but also some bacteria Bacteria are extreme thermophiles as well. Now, let me ask you a question.

Let me test your understanding. Looking at these different temperature types, which of these five would you suspect would cause the most human diseases, would be the culprit of the most human diseases and be... known human pathogens or most likely to cause an infection in a human.

What do you think? Can you beat Wicked? That's right. That's right.

Wicked is always mesophiles. Well, think about it. Mesophiles prefer 37 degrees for growth.

Your body is at 37 degrees. So, you know, yes, it's most of the human pathogens are mesophiles. Why? Because those pathogens want to grow on your body because they prefer your body's temperature. Moving on to our next environmental condition for growth, gases.

Different microbes prefer different gases for growth. Atmospheric gases contain oxygen and CO2. You also have nitrogen in the atmosphere as well.

Well, some organisms can grow in the presence of oxygen, and some organisms, they cannot grow in the presence of oxygen. There are three categories of organisms with respect to oxygen. Those organisms that can use oxygen and detoxify it, those that neither use oxygen nor detoxify it, those that do not use oxygen but can detoxify it. So let's delve into this concept of using oxygen and detoxifying oxygen and discuss what this all means.

Well, as it turns out, oxygen can be quite tough. toxic to the cell. It can destroy cells, but not in its normal form of oxygen gas, O2. It's when, take a look here, as oxygen enters into cellular reactions, such as metabolic reactions in a cell, it is transformed into several toxic oxygen products. These are known as ROS, or reactive oxygen species.

For instance, singlet oxygen, which is a single O, a single oxygen, is extremely reactive. And it's produced by living and non-living processes. This singlet oxygen, if it's present in your cells, it can cause cell damage and cell death because it can cause oxidation of your cellular components.

Again. This buildup of singlet oxygen and the oxidation of membrane lipids and other molecules can damage or destroy the cell. Here's another reactive oxygen species.

It's called superoxide ion. It's O2 with a negative charge. Here's another one, hydrogen peroxide, H2O2. And here's a third one, hydroxyl radical, OH-. All three of these are examples of ROS.

reactive oxygen species which is created by cells during cellular reactions that can cause damage to the cell so much damage that it can kill the cell so when these when these ross molecules build up in a cell they need to be neutralized they need to be dealt with otherwise they could result in cell death so only those organisms that can neutralize these ross can live in the presence of oxygen. I hope that makes sense. So for instance, cells use enzymes that they code for with their genes to scavenge and neutralize these ROS in a two-step process.

So for example, step one, the enzyme that's produced by a bacterium or a microorganism, this enzyme superoxide dismutase will convert superoxide radical or superoxide ion 202 minus it'll it'll convert that to hydrogen peroxide right hydrogen peroxide still a form of ross it is a reactive oxygen species however the second enzyme again coded for by a microbial gene the enzyme catalase will then take that hydrogen peroxide and convert it to harmless water so you see Organisms that have these two enzymes, superoxide dismutase as well as catalase, they are capable of neutralizing dangerous ROS, like this superoxide ion as well as hydrogen peroxide. However, an organism that does not possess superoxide dismutase nor catalase, it will have a buildup of superoxide ion or even hydrogen peroxide, and those reactive oxygen species would destroy the cell, again, by attacking the membranes, again, by causing oxidation in the cell, killing the cell. So those organisms that can grow in the presence of oxygen need to create these enzymes or have these enzymes. Those that can't grow in the presence of oxygen tend to lack these enzymes. So with regard to oxygen requirements, aerobes or aerobic organisms are organisms that can use oxygen during metabolism.

These organisms do not get destroyed by reactive oxygen species. This is because they produce the enzymes needed to process those oxygen products. Remember superoxide dismutase and catalase. In fact, there are even organisms that are obligate aerobes.

An obligate aerobe is an organism that must grow in oxygen. It cannot grow without oxygen. There's another class of organisms called facultative anaerobes. And these organisms, they don't require oxygen for metabolism, but they are capable of growth in the presence or absence of oxygen. These organisms can grow in the presence or absence of oxygen.

The way they do that is they undergo aerobic respiration when oxygen is present. And then they switch to fermentation when oxygen is absent. Another class are the microaerophiles. These organisms, they do grow in oxygen, but only low levels of oxygen. So they do not grow at normal atmospheric concentrations of oxygen.

The amount of oxygen in the atmosphere is between 20 and 22 percent. And these... organisms do not grow in that range. They prefer lower concentrations of oxygen, for instance, 8 to 10% oxygen.

Anaerobes or anaerobic microorganisms, these are organisms that grow in the absence of oxygen. If it's a strict or obligate anaerobe, this means that it lacks the metabolic enzymes. necessary for processing oxygen.

So for instance, because strict or obligate anaerobes do not produce the enzymes superoxide dismutase or catalase, they are not capable of processing those reactive oxygen species like singlet oxygen or superoxide ion or hydrogen peroxide. And then they succumb to those reactions. oxygen. So where you find anaerobes, specifically strict or obligate anaerobes, is places that have deep in the mud, lake, ocean, soil, where there's very, very little to no oxygen.

And the last class here are the aerotolerant anaerobes. These do not utilize oxygen, but they can grow to a limited extent in its presence. And the reason they can withstand oxygen is because even though they don't use oxygen, they have ways of breaking down peroxides and superoxide radicals.

And here we can see bacteria with different oxygen requirements growing inside of broth. Here you can see if the bacteria only grows at the surface. This is an example of a obligate aerob. If it grew just below the surface, just here, but only just below the surface, that would be a microaerophile. If it can grow in the presence or absence of oxygen, then we're talking about a facultative anaerobe or an aerotolerant bacterium.

And if it only grows at the bottom of these tubes, then it is a obligate anaerobe, a strict anaerobe. Speaking of gases, some microbes prefer high levels of CO2. These are called capnophiles.

Capnophiles grow best at higher CO2 levels than normal atmosphere. Moving on to our next environmental condition, pH. Parts of the earth have different pH environments. There are acidic environments. There are basic environments.

There are neutral environments. and each of those environments has organisms that prefer to live in there. Remember that pH is expressed on a scale from 0 to 14, 0 being very acidic, 14 being very basic or alkaline.

pH 7 refers to a neutral pH. Organisms that prefer acidic pH for growth are called acidophiles. Obligate acidophiles, as the name suggests, must grow in acidic conditions. Conversely, alkalinophiles prefer alkaline or basic pH environments for growth. Moving on to our next environmental condition, osmotic pressure. These typically refer to hypertonic conditions.

Environments with... high solute concentration, for instance, high salt concentration. In fact, osmophiles are organisms that prefer to live in habitats with high solute concentration. Halophiles, as we've discussed before, halophiles, these are organisms that prefer high concentration of salt for growth.

Obligate halophiles need high levels of salt for growth, while facultative halophiles, they can grow in the presence of high salt concentration, but they do not need high salt to grow. So for instance, Staphylococcus aureus. It grows on your skin and it's salt tolerant, right?

It does not mind that salty environment of the skin. A non-halophile would not be able to grow on the skin. This is why skin infections are often caused by staph. Staphylococcus aureus, Staphylococcus epidermidis. These are bacterium that are halophiles, facultative halophiles.

And they prefer to grow on the skin. Other bacteria may not be resistant to the salt levels present on the skin. And so this is why skin infections tend to be caused by staph or another salt-tolerant microorganism.

The next environmental factor, radiation. Phototrophs use visible light. Visible light is a type of... electromagnetic radiation. But phototrophs use visible light radiation as an energy source.

And there are other forms of electromagnetic radiation that stream onto the earth from the sun as well as visible light. These include ultraviolet or UV light, infrared light as well. Non-photosynthetic microbes tend to be damaged or destroyed by radiation, specifically UV light. UV radiation. Another type of radiation that can damage microbes is ionizing radiation, x-rays or cosmic rays.

So some forms of radiation are required for life, such as visible light radiation to photosynthetic organisms. And some forms of radiation are deleterious to life or damage life forms, including ultraviolet or x-ray or cosmic rays as well. Moving on to another environmental factor, hydrostatic pressure. Deep in the ocean, there is high pressure of water. There's high water pressure.

And it's the beryl files that can live in this high water pressure, deep sea environment. Moving on to the next environmental factor, moisture. Moisture is required for bacterial and microbial growth. Remember that most of a cell's contents is water.

Most of the cell's mass is water. So it's very difficult for microorganisms to grow in a water-free environment. And it's only those dormant dehydrated cell stages, such as spores or cysts, that can tolerate.

extreme drying because their enzymes go inactive. Living organisms cannot tolerate extreme drying or desiccation. Now that we've covered the different environmental factors that can affect microbial growth, let's discuss associations between organisms. Namely, we're going to talk about symbiotic associations. We're not going to delve too much into non-symbiotic relationships in this class.

Symbiotic relationships are when organisms live in close nutritional relationships. Symbiotic relationships are when two different species coexist. They live together.

However, this can be beneficial or this can be harmful. Let me explain. One type of symbiotic relationship is a mutualistic symbiotic relationship.

This is the one that people think about when they think about symbiotic relationships. This is when both members benefit. Both of the members are benefiting from one another. This is called a mutualistic symbiotic relationship.

However, a commensal symbiotic relationship is when the commensal benefits, the organism that lives on the host benefits, but the other member is not harmed. Now, during parasitism, which is another type of symbiotic relationship, parasites depend and benefit from the host. but the host becomes harmed. The host is harmed, the parasite benefits.

And again, students don't usually associate parasitism with symbiosis, but it is a form of symbiosis. So we should know the three different forms of symbiosis. Now one type of association I will talk about are biofilms.

Biofilms are mixed communities. Communities refer to different species. of different kinds of bacteria and other microbes all living together and helping each other out.

And here's how a biofilm works. Let me give you an example. An example of biofilm would be the plaque on your teeth, right?

The plaque that grows on your teeth that you need to brush off at the end of the day. So here's how a plaque forms. Here's how a biofilm forms. First, pioneer bacteria.

bacteria colonize a surface. So certain bacteria, for instance, they will adhere to the surface of your tooth enamel. This would be your tooth enamel in the background.

And remember, they use adhesion structures such as fimbri or slime layers or even flagella in order to stick to the tooth surface. At this point, what's really cool is that These pioneer organisms will secrete an extracellular material that helps keep them on the surface and serves as an attachment point for later colonizer. They start secreting this goo. And this goo is sugary, proteinaceous goo.

And this goo allows other organisms to also attach to this matrix. And at the same time as they're... They're producing this gray goo. They're producing these little red structures. These are called quorum sensing chemicals.

Quorum sensing chemicals are chemicals that are released by each of these microorganisms. Each of these bacterium release these quorum sensing molecules. And when a certain concentration of quorum molecules builds up, that triggers a a quorum sensing event. In many, but not all, biofilms, other species join and may contribute to the extracellular matrix, this sugary proteinaceous matrix, and or participate in quorum sensing. Remember, quorum sensing refers to releasing these quorum molecules.

Once, again, once a threshold concentration of these quorum molecules has built up, These quorum molecules will reenter these cells and trigger more biofilm formation. So let me explain. Making a biofilm, making a biofilm makes no sense if you're all by yourself, you know, because it's expensive to secrete sugary proteinaceous matrix.

You know, this, this goo, uh, it's expensive for the cell to release this goo. If there's one or two cells. They may not want to expend the energy necessary to secrete this goo.

And so it's better to save your resources and not secrete the goo if there is no other bacterium around. And how do you know if other bacterium around? That's where the quorum sensing molecule comes in.

Each bacteria releases this quorum sensing molecule. Once the quorum sensing molecule builds up to a high enough concentration, Then it triggers the formation of the goo. It triggers the formation of the extracellular matrix, this sugary proteinaceous matrix, which then allows other organisms to help colonize this biofilm. And the biofilm matures. A mature biofilm may stop or minimize quorum sensing.

And then at that point, other bacterium can go planktonic again, and they could spread and... go and start another biofilm at this point as well. And by the way, where did quorum sensing get its name? Do you know? In model Congress or in Congress, anytime you have congressional meetings with congressional structure, you have what's known as quorum.

This means that a certain percent of the members need to be present in order to start the proceedings. These are called quorum molecules because they ensure that a that a significant number, a satisfactory number of microbes are present in the environment in order to start the process. In this case, it's to create the extracellular matrix, this, this kind of, um, sugary proteinaceous biofilm in that interesting, again, if you're all by yourself.

You're not going to reach that threshold concentration of quorum molecule. If you're high enough density, high enough population, then you will have more than enough of this quorum sensing molecule to trigger more biofilm formation. So quorum sensing is a way of bacterium realizing or sensing how many other bacterium are in the environment. The reason for quorum sensing is to make sure or ensure that costly cellular activities, such as making a biofilm, only occur when there are sufficient numbers of microbes in the environment.

Isn't that neat? A long time ago, it was assumed that microbes had no way of communicating with one another until quorum sensing was discovered. So quorum sensing, again, it occurs when a bacterium, it makes more sense for them to do that cellular activity as a group than it would alone.

So for instance, again, making a biofilm, it makes more sense to secrete that sugary proteinaceous matrix, that biofilm, if you're in a large group and doesn't make sense to waste those resources. If you're all by yourself, another example, making a toxin, some bacterium, they won't make a toxin. against a host unless there's again quorum sensing and a sufficient number of bacterium in the environment another example did you know there are some bacterium that can glow like deep fish bacterium the bacterium that grow deep in the ocean where there is no light okay these bacterium can glow but only when they're in high concentrations in the pockets in the fish you know, in different pockets in the fish membrane and the fish skin. Isn't that interesting? So these organisms will not glow if they're all by themselves, but they will glow due to quorum sensing in a high population.

Isn't that neat? Again, bacterium use quorum sensing in order to do cellular activities that makes sense to do in high populations and not alone. Now for the last part of this chapter.

Let's talk about population growth, bacterial population growth. Bacteria grow, not by mitosis, but by a process known as binary fission, which is much more straightforward and simple than mitosis. Here's a bacterial cell. You've got this stringy stuff, which is the nucleoid, right?

The single circularized chromosome, the nucleoid. Here you have ribosomes as well, those little dots. this is a young cell. This cell will grow.

They will elongate. You see how the cell elongates and the nucleoid is copied. Now you have two copies of that single circularized chromosome. Those two copies move to opposite ends of the cell. And then a protein band forms at the center of the cell.

This is known as the FITZ band. And then this promotes, uh, cytokinesis. Remember cytokinesis, the separation of the cell itself. And cytokinesis occurs by a process known as septum formation. Septum formation, which is an inward growth of the cell wall of the bacterium.

When the septum is complete, the two bacterium are separated from one another. However, sometimes they can remain attached. And this is how staphylo arrangements can form or strepto arrangements might form or diplo arrangements might form if they don't fully separate. Now let's discuss bacterial rate of population growth.

How fast do bacteria divide? This is known as the generation time or doubling time of a bacterium. It's the time required for a complete fission cycle.

This means one young bacterium growing, elongating, and ultimately becoming two identical copies, right? Dividing into two cells. Hi, Wicket.

Wicket has come to say hi. He's on the table right now. Hi, buddy. Wicket.

Wicket's come to say hi. Wicket. Always so fun having wickets come say hi.

Hi buddy. Hi sweet buddy. What are you up to? Oh gosh he's scratching.

He loves to scratch my monitor. So that's what you're hearing right now. We're taking an impromptu break time with Wicket. Wicket's here to say hi.

Oh, he's very excited to visit. Hi, buddy. Hi, buddy.

Do you hear him purring? I wonder if you can hear him purring through the microphone. Let's listen really close. What are you up to, Wiki? One thing to keep in mind about the generation time is that with each new fission cycle, each generation time.

This doubles the population of the bacterium. So long as the environment remains favorable, the doubling effect can continue at a constant rate. Here we can see the cell division doubling time in the population.

If we start with a single bacterium, the number of cells is one. The number of generations is zero. And to understand how many...

bacterium are present at this point, we take two to the power of the number of generations. In this case, the number of generations is zero. So we have two to the power of zero organisms, and that equals one. There's one organism at time zero, at generation time zero. At generation time one, by the way, many bacteria...

bacterium divide between 25 minutes and 35 minutes. So this is very fast for many bacterium. They divide quite quickly. So let's say within 30 minutes, the bacterium would double from one bacterium to two, right? Because that cell underwent binary fission.

At this point, you have one generation, one doubling. And the number of cells would be 2 to the power of 1, or 2 total cells. Then, 30 minutes later, those two double. So if both of those double, now you have 4 cells. This is your second generation.

To calculate the number of cells, you take the base of 2 to the exponent 2, because there have been two doublings, and 2 to the power of 2 is 4. And we can go on this way. So this is known as a logarithmic growth scale with the base two. These are the number of log base two doublings.

And because this is a logarithmic growth, populations can explode in a short amount of time. In fact, for E. coli, for instance, it could take E.

coli 25 to 30 minutes to divide. If we start with a single E. coli, it takes five hours or so, give or take, to make a million E. coli. So from one bacterium, one E.

coli, it would take about five hours to make a million. And I always ask myself, I always ask my students, let's see if you can beat Wicket. If it takes one E.

coli, five hours to... result in a million E. coli, right, to divide and become a million population, then how long would it take for another million, for two million to form?

Can you beat Wicket? All right, Wicket, good job. Another 20 minutes.

So it took five hours to get your first million E. coli. But it would only take another 20 minutes to get your next million.

Remember, it's exponential growth. Every doubling time, you are doubling the population. So yes, Wicked is right. It would only take another 20 to 25 minutes to result in 2 million E. coli.

This is because the doubling time of E. coli is roughly 25 minutes. Isn't that neat?

So this is why... when we plate ourselves on media, you know, if you make like a spread play or a streak play. Then you put those plates in the incubator and we come back, remember, two days later, three, four days later, you know, and we take a look at those plates. What do we see on those plates?

We see a bunch of bacterial growth. And each one of those colonies represents millions upon millions upon millions of, you know, E. coli or whatever species you're studying. And the reason why you see those colonies is because a single cell.

divided exponentially right with a base of two they doubled every 20 25 30 35 minutes depending on the species and that resulted in a colony by the time you returned so a single cell became millions upon millions if not billions in a few short days this is also why we refrigerate our food for instance You know what happens when you take food out of the refrigerator? Any microbes that happen to be on that food start to divide, right? Because they were not dividing so fast in the refrigerator, but you remove that food from the refrigerator and those microorganisms start to divide. And remember, they divide exponentially. So there might be just a few E.

coli on your, you know, potato salad when you removed it from the... from the refrigerator, but you left it on the counter. Well, guess what?

After five hours on the counter, each one of those E. coli is now a million, right? And if you leave it for another 20 minutes, each one of those E. coli is now 2 million.

And now if you were to eat that warm food that's been sitting out, you know, now you would get food poisoning. You would come down with an illness, right? However, if you had refrigerated that food, then those bacterium would not have divided so fast.

Your food would not have spoiled and you would have been fine eating that same potato salad if it had been properly refrigerated. So now we know the importance of refrigerating our food, right? And it's all based on this chapter.

This chapter is so interesting. It explains why we refrigerate our food. Why?

Because many organisms that cause human diseases are these organisms that are mesophiles. Remember, mesophiles grow best at human body temperature. If we're keeping our food in the refrigerator at four degrees C, then that's below the minimum growth temperature of many mesophiles.

So those microorganisms can't grow. And if they can't grow, they don't form sufficient concentrations to cause human disease or food poisoning. But if you remove the food from the refrigerator, those microorganisms begin to animate. They begin to grow and divide exponentially with logarithmic growth.

And next thing you know, you have food poisoning. So isn't that interesting? Also, All the other environmental conditions play a role as well.

So for instance, remember, not all microorganisms can grow in high salt. So this might be why we salt our foods, to preserve them. Have you heard that salt is a preservative, a very important preservative?

And by salting our foods, we can preserve them and prevent bacterial growth and for the food to become spoiled? bacterium are halophiles. Only halophiles can grow in high salt. And so by doing that, we reduce the number of microbes that grow on the food.

Also dehydrating. Why does steak go bad so easily if it's left at room temperature, but not beef jerky? Beef jerky is just dried out steak. So remember, many organisms, all organisms require moisture to grow. Beef jerky is too dry to grow on, right?

There's not enough moisture for the microbe to grow on that surface. Isn't that interesting? Also, why do we pickle our foods?

You know, when you pickle a food, it makes it more preserved. It keeps its shelf life much higher. You know, pickles last a lot longer than cucumbers, don't they?

Well, why is that? Well, because it's an acidic pH. It's an acidic environment. And again, only acidophiles would want to grow in that environment.

Isn't that really neat how this chapter kind of plays into how we treat food? And it should also play into how we treat, you know, the clinic in the medical setting in order to help keep the health of our patients in order to prevent the spread of disease. The better you understand microorganisms and their growth requirements, as is the topic of this chapter.

the better you can treat for your patients, but also the better you can stay healthy at home and with your own food, you know, in your own kitchen. Isn't that neat? Okay, again, if we plot bacterial growth on a log scale, then it is a linear logarithmic growth of bacterium over time.

However, if we do not use a log scale, it appears like the bacterium grow asymptotically. They grow exponentially, but they form kind of this asymptote as they grow. So normally when we're talking about bacterial growth, we depict it on a logarithmic scale so that you see this nice straight line here.

And for the last concept from this chapter, let's talk about a population growth curve. A growth curve is a predictable pattern of growth in a population of bacteria. Specifically, let's look at a growth curve in bacterial culture. This is also known as batch culture.

If you have, let's say, a limited environment with limited resources, limited nutrients, and limited space. So, for example, what if I have nutrient like TSB broth inside of a test tube? Do you agree that there's limited nutrients in this broth?

Limited space in this broth? Well, that's what bacterial culture means. There's limited resources. So like imagine a flask of broth or a test tube of broth.

Well, when we have a test tube of broth and we seed it with some E. coli, we seed it with some bacteria, there are one, two, three, four very predictable growth curves that occur. And this is how it works. On the y-axis, we have the log scale of viable cells. So we have the log scale of cells.

These are living cells. And on the x-axis, we have hours, number of hours. So when I place E.

coli, this many E. coli into broth, at first, there's always what's known as a lag phase. During the lag phase, this is a flat. period on the graph when the population appears not to be growing.

This is because newly inoculated cells, remember I said I just added some E. coli to this environment, I recently inoculated the environment with E. coli, these require a period of adjustment, enlargement, and synthesis.

Cells just can't multiply at their maximum rate. So here, during the lag phase, the bacterium are becoming active. acclimated to their environment. Then at some point, now that they're acclimated to their new environment, they enter what's known as the exponential growth phase.

Remember, this is the log growth phase where the bacterium double and double and double and double every generation time, every doubling time. However, at some point, we enter the third phase of the bacterial growth curve phase. Here we see it's called the stationary phase.

At this point, the party's kind of over. We've exhausted all the nutrients and the space, and the bacterium can no longer grow. So at this point, we enter stationary phase in which no doubling is occurring.

No bacterial doubling is occurring. And then after a period of time, we enter our final phase, the death phase. Because these bacterium have... been stewing in their own waste, you know, because there's waste in here. There's no nutrients in here.

They become sick and a number of cells die off. And this is known as the death phase, sometimes known as the senescence phase. And that's it for this chapter.

We talked about all of the nutritional and growth requirements for bacterial cells and microbes. I hope this chapter was informative. It was really interesting reflecting back on.

how we treat our food and how it has everything to do with the bacterial, nutritional and environmental growth requirements. So I think that's neat. I hope you found it neat as well.

Please let me know if you have any comments in the comment box below, and I will catch you guys next time. Dr.

Transcript for:Understanding Microbial Nutrition and Growth

Transcript for:
Understanding Microbial Nutrition and Growth