To maintain cells in that exponential growth phase, we have to consider many factors that affect microbial growth. In particular, temperature, pH, water availability, and oxygen, all of which we're going to cover in these next few slides. We're going to start by considering temperature, and as with many of the growth conditions that we will consider, they are impacting these conditions will impact the molecular components of the cell. If the cell is too cold, i.e. it's acting at its minimum cardinal temperature, the membrane will lack fluidity. It will actually start to get solid-ish, so it gels, and that will actually impact transport to the point where they're unable to bring molecules in.
they're unable to export molecules out and growth will slow down and eventually stop. On the other hand, if we look at the maximum cardinal temperature, at this point the membrane is unable to maintain its structure. It's too fluid and so at that point we may actually see thermal lysis occurring where the cells will burst open. And in addition, at these higher temperatures we're also going to see protein denaturation where the proteins will be unable to function.
And as we know, proteins pretty much do everything in our cells. To maintain that cell in that exponential growth phase, the cardinal temperature must be optimal for that organism. Now, if you remember from previous classes, there's a particular part of our enzymatic reactions that we're concerned about with temperature.
For every 10 degrees rise in temperature, we actually get a doubling in enzymatic reaction. So we want to be as hot as possible because that means the enzymes are working at their optimum. So organisms will always thrive at these upper temperature regions. So that's why you can see right here that they're leaning towards the right here instead of being a straight up curve like we saw previously.
So this is not a growth curve. This is a way of looking at temperature growth and rates. So at these optimum ranges, the membranes are intact and the proteins are not denatured, and they're also acting at their optimum. Microorganisms can be grouped by their temperature ranges that are required for growth.
So we're going to go through all of these different types of conditions. You are not to know the exact temperature ranges nor are you expected to know these particular bacteria or archaea which we'll go through as well. What you are expected to know is these classifications and what they mean and we'll go through each word so you should be able to break them down relatively easy. The other thing I just want to point out on this particular graph is what you're going to see is this trend of always leaning to the right because remember This is the optimal growth, the optimal cardinal temperature right here.
So let's get started. So we're going to start with our psychrophiles. So psycho is Greek for cold and phile means to like. So these organisms therefore like cold temperatures are normally found in unusually cold environments. For example, Polomonas vaculata, which If you see polar, you start thinking that it's coming from one of our polar climates.
So it's actually isolated from Antarctica and likes to live in these very cold conditions. Now, we also have our mesophiles. Meso means middle. So middle liking organisms. So these are mid-range organisms.
These are found in warm-blooded animals. So there are particular... concern for us. They're also found in terrestrial and aquatic environments, temperate and tropical latitudes. These are also the ones you're going to find in your hot tub as well.
Now you can see optimal cardinal temperature is around 39 degrees Celsius, which I find is really interesting. And a great example here is E. coli.
So if you remember our body temperature is 36.9, but these are optimally at 39 degrees Celsius. And we're going to come back to that. during class. Thermophiles, thermo meaning heat or hot, so these organisms like the heat and they have elevated temperature optimum.
These are usually found in unusually hot environments, for example Geobacillus stereothermophilus. So you can start seeing some of the names are also kind of giving us an idea about what kind of environments they like to live in and this one's found in soil, hot springs and ocean sediments. Then we have our hypothermophiles. So these really like heat. So they have very high temperature optimum found in hot springs, geysers, deep sea, hydrothermal vents, for example, Thermococcus cellar and also Pileuberus fumari.
This is a species of archaea discovered in hydrothermal vents. And the optimum temperature for this particular organism is about 113 degrees Celsius. So the organisms, these ones that we're talking about here, the thermophiles, the hypothermophiles, these that live in these upper extremes and also the ones that live in these lower extremes are often referred to as extremophiles.
So that's something that you're going to see fairly frequently and extreme meaning extreme environments.