hey everyone Dr D here and in this video we are covering chapter four from our microbiology ass systems approach uh book uh by Cohen 7eventh Edition this chapter covers bacteria and archa so let's go ahead and get started Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D explain stuff all right to start please remember that bacteria and ARA they are pro carots and so they do not have a nucleus instead they have what's known as nucleoid UK carots on the other hand they have their chromosomes inside of a double membrane called the nucleus that's the main difference between UK carots and procaryotes the presence of a nucleus as well as the presence of other other membranebound organel UK carots have membrane bound organel procaryotes don't membrane bound organel include the main one the nucleus but also other membrane bound organel including you know the mitochondria the chloroplasts the Gia apparatus the endoplasmic reticulum vacul all of these are membranebound organel and bacteria and Aran they lack these structures they do have chromosomes right bacteria and ARA they typically have remember one circularized chromosome um but they that DNA that chromosome is floating around in the cytoplasm as a structure known as the nucleoid and here in this figure you can see a typical procaryotic cell this is a bacterial cell a typical bacterial cell in it you see the fluid this blue fluid is the cytoplasm which is this fluid inside of the cell and this stringy stuff you see these purple string that's the nucleoid that is the DNA and remember the nucleoid is usually a single circularized chromosome and it's all packaged up into this nucleoid structure so if I were to take this stringy stuff out that DNA out and untangle it it would really have no beginning and no end it would be a closed circle of double strand DNA these other little dots here you see these little blue dots these represent ribosomes bacteria ARA and ukaria all have ribosomes all cells have ribosomes ribosomes are there for synthesizing proteins they're essential for making proteins as well um you know nor uh all cells also have a plasma membrane see this in Gold here that's the plasma membrane all cells have some kind of plasma membrane but bacteria in particular check this out bacteria have a cell wall usually bacteria have a cell wall a semi- rigid casing that provides structural support and that cell wall is made up of a component which we're going to talk about in a little bit called peptidoglycan peptidoglycan makes up the cell wall of bacteria and by the way peptidoglycan is unique to bacteria that means only the domain bacteria have pepti glycan cell walls then there could be additional layers there could be outer membranes there could be additional layers there could be capsules there could be all kinds of stuff on the surface of the cell we're going to talk about all these structures they could be fimy on the outside of the cell this look like these little hairs there could be flagel you see like a flatulum a procaryotic flatulum so these are typical structures inside of a procaryotic cell there can also be what are known as inclusions which are storage areas inside of the cell there could be plasmids little circular DNA inside of the cell there could be all kinds of structures inside of a typical procaryotic cell and that's the purpose of this chapter we're going to delve into this uh procaryotic cell and we're going to talk about all the typical structures inside of procaryotic cells specifically we're going to focus on bacterial cells and of course bacteria are alive bacteria they comprise one of the three domains of life they are single cell organisms fully capable of reproduction metabolism nutrient processing and more all of the characteristics of life bacteria can even act as a group sometimes bacteria can form colonies they can form biofil which are communities and we'll talk about these biofilms in a little bit and being procaryotic in nature these bacteria are very small they are an average of one micrometer in diameter now some bacterium they can range you know a typical bacterium is between one and let's say five micrometers in diameter and that's about 10 times to 50 times smaller than the average eukaryotic cell UK carots are about 10 to 50 micrometers in diameter however these bacteria they can vary in their size their shape and their Arrangement as well and we're going to touch on that with respect to shape bacteria have three common shapes they can be cockus shape which means spherical basilis shape which means Rod shaped or they could even be spirillum or spiral shaped hey Wicket Wicket is here to say hi uh he is scratching at the uh monitor right now so thanks hi thanks for the visit Wicket I always enjoy a visit from Wicket oh gosh and he's running into things but getting back to bacterial shapes again the most common of shapes you're going to find for bacterium are caucus shape which means spherical basilis shape which means Rod shaped and a spirillum which means spiral shaped but that's not the only type of shape where we can have we can have other shapes as well some bacterium can be oval shaped Bean shaped pointed blocky spindle shaped round with rounded edges they could be filamentous there's actually an entire class of bacterium that are filamentous they have these filamentous cells kind of like fungi you know molds they can have hyle cell shaped they could be Club shaped or drumstick shaped with regard to the spirillum not only can you have spiral-shaped bacteria but you can have cork screw shaped SP uh bacterium which are fullon spirals uh you could have vibrio bacterium vibrio look like comma like a comma shaped so there are so many different shapes of bacterium out there but the most common again are cacus basilis and spirillum now some bacterium have no shape whatsoever and these are known as the pomor bacterium these pomor bacterium because they lack a cell wall they don't have a particular shape so they're going to have various shapes now let's talk about arrangement we talked about shapes right the common shapes caucus basilis spirillum but what about Arrangements those shapes can adopt various arrangements so let's talk talk about these Arrangements Diplo Diplo is a Arrangement which means pair so if you were to describe a bacterium as Diplo coxy it would mean that the bacterium hang out as pairs of spherical bacterium see so coxy refers to the Spheres Diplo refers to its Arrangement that means pairs of spheres tetrads would be groups of four so for example tetrad uh you could have a tetrad of coxy staf staf when you see this term staffo you should know that refers to irregular clusters grapelike clusters so if you see the term staf coxy this means grap likee clusters of spherical cells the first part of the word staf refers to the arrangement the second part of the word coxy refers to the shape strepto on the other hand means chains like think of uh you know a pearl necklace think of um forming a chain forming a row uh strepto coxy would be bacterium that form a CH chain of spherical bacterium and then there are sarinia SAR are cubal packets either a cube of eight a cube of 16 or even more and these are all different Arrangements that coxi can have that spherical bacterium can have what about basili remember basili are Rod shaped bacterium basili can exist as pairs as as well called Diplo basili that means a pair of basili or rod-shaped cells strepto basil which is a chain of these cells end to end Palisades which are these Rod shaped cells uh which are side by side so imagine you know strepto is end to endend Palisades are side by side spirilla remember spirilla are these uh cells that have a curved shape or like a spiral shape spirro spoets they have a cork screw shaped sometimes you can find spirilla in short chains but spirro kits are rarely attached to other cells now remember bacteria exist as single cell creatures however they can form communities and remember in bi ology a community consists of various species different species living together and in a bofilm for instance bacteria that form biofilms this consists of a community of different species all living together inside of a polysaccharide and sometimes it has polypeptide Matrix a sugary protonation Matrix think of think of different bacterium take a take a look at this picture here you have all these different bacterium all living together in a community and that Community exists in a sugary protein proteinaceous secretion that they make so they secrete this sugar they secrete this protein and that makes this gooey surface in which different organisms can live together and they can help each other and sometimes it's symbiotic even they can help each other to grow so they call these biofilms Cooperative associations with organisms of the same species as well as other species of bacteria even arcaya fungi and algae you can have this this Cooperative Community biofilms are microbial habitats with access to Food Water atmosphere and other environment factors that are beneficial to each organism type living there best example of a bofilm I can give you are for instance the you know the biofil on your teeth you know when you when you when you don't brush your teeth for a while they feel a little bit kind of fuzzy you know you run your tongue on your teeth and it feels like there's something there like it's not so smooth and that is plaque right that's a bofilm that's a type of bofilm that's forming on on the tooth surface and so that's a community of bacterium that are attaching to the tooth and growing so how does it work let me show you at first whoops at first you have a surface let's say this is the surface of your tooth different bacterium will attach to the surface of the tooth these are known as the first colonists once they attach they will secrete that Sugar I told you about remember they can they can they can secrete a sugary proteinaceous uh secretion which is going to become the bofilm next as cells divide they form a dense mat bound together by sticky extracellular deposits these extracellular deposits they're referring to is the sugar it's this glycocalix which is a sugary proteinaceous structure and it's imagine being covered in goo and secreting goo next thing you know additional microbes of all different species remember all different species even different types of organisms like fungi or algae they can they can attach they are attracted to this bofilm that's forming they attach and they create a mature Community with complex function so what does that mean that means they could almost help each other out for instance let me give you an example of how fun this could be this bacterium for instance it might it might convert nitrate to a waste product nitrite now this other organism May convert the nitrite to ammonia and then the last organism might convert ammonia to nitrogen gas you see how that would be cooperative the waste product of one organism might be the necessary nutrient of the next organism and so you form this Community where you're all kind of helping each other out you're you know there it's a Complex Community with intricate uh you know networks of of uh cooperation going on and that's what's happening believe it or not in on your tooth surface and why it's so important to brush your teeth right you got to brush your teeth because you know once these communities form on the tooth surface every time you take in some sugar or you you have a sugary treat these bacteria they start secreting acids and they start wearing down that enamel of your tooth so this is why it's so important to brush your teeth all the time because biofilms form on the tooth every time you eat sugar they digest the sugar and make acidic waste products that wear down your tooth enamel um but yeah scraping these guys off is the only way to do it right so you got to scrape them off by brushing next let's talk about bacterial appendages these are things that hang off the outside of bacteria not all bacteria have these appendages but some do two major groups of appendages are the ones that provide motility so for instance fagula for motility or an axial filament for motility we'll discuss these and then external appendages that provide attachment points or that form channels these are known as FR pilli or even nanowires now we're not going to address nanowires in this chapter but just be aware that they exist we're going to focus on fim and pilli as attachment points now here's a flula a flula you know is a long whip-like structure that some bacterium possess and some bacterium possess numerous fagula um but a flatula is there for motility a flula consists of this long whip-like tail called the filament the filament is a long whip-like tail made up of proteins long whip-like structure of proteins flagin proteins to be specific that long whip-like structure the filament is connected to an L-shaped hook the hook is what connects the filament to the basil body the basil body you could think of it as the motor the motor part of the Flaga the the reason the Flaga works and that basil body is embedded into the cell envelope of the bacterial cell it's embedded into that cell wall of the bacteria so you see here these ring like structures are the basil body of the of the flatulum then you have the hook and the filament I also want to turn your attention to this blue arrow you see this blue arrow it's suggesting rotation and that's for a good reason the flatula rotates it literally spins and Spins and Spins imagine if this ring structure here the basil body imagine if it was spinning right this the the hook was spinning around and around and around the way I ex I explain it is imagine if you attached a a whip to a boats propeller right you attach a whip to a boat's propeller and then you turn on the boat propeller what would happen to that whip it would just spin around and around and around right so that's how a bacterial flula Works a bacterial flula spins and Spins and Spins thanks to the basil body Motors isn't that neat so think of it as a rotary motor these bacteria their flatula is spinning and spinning and spinning and that spinning is what provides the motility and what's interesting interesting is that not all bacteria have a Flaga some bacteria have no Flaga these bacteria are called a trius bacterium these have no flagellum whatsoever when you see this suffix trus you should think flag Arrangement so if a bacterium is a trius a the the prefix a suggests that there's no you know or in a trius bacteria lack a flatulum while monot trius bacterium have a single flatulum and if it's a mono trius polar flatulum that single flatulum is attached at one end of the cell now lot trius bacterium they have a small Bunch or a TFT of flatulum at one spot so for instance look at this character here look at this bacterium you see how it has like three or four flagellum at that one spot that's known as a TFT lot trius bacterium have a tuft they have several flatulum at one particular spot amphit trius bacterium they have a flatula at both poles of the cell so they have one at each end of the cell per trius bacterium these are superstars in motility because they are completely surrounded with flatulum so here you can see this character right here this is a this right here is a perus a perrus bacterium it's completely surrounded with flatula um this one here was an uh lopo trius it has a tuft it has several flatulum at one spot here you can see a monot tray IUS bacterium it has one really large uh back uh flatulum one large flatulum so you can see that bacterium have various arrangement of flatula some have none some have one some have two some have a TFT and some are completely surrounded and so not all bacteria are modal some bacteria are not modal once what whatsoever those are the Atrius ones so what is motility good for motility allows the bacterium to move towards nutrients and away from hazards or toxic substances this is known as chemot taxes when you see taxes the suffix taxes this means directed cell movement directed cell movement movement if it's chemotaxis we're referring to movement towards or away from a chemical if it's phototaxis we're talking about movement towards or away from light usually towards light now look here chemotaxis again this is movement in response to chemical signals if you're moving towards the chemical this is known as positive chemotaxis so imagine there's a favorable chemical such as sugar the bacterium will move towards the sugar that's positive chemotaxis now what if there is a repellent or a potentially harmful compound let's say there's an antibiotic around right the bacterium doesn't want to get anywhere near that toxic compound or that harmful compound that would be negative chemotaxis because the bacterium could set a course away from that chemical gradient with phototaxis some bacterium actually move towards light um especially the photosynthetic bacterium remember there's a whole class of photosynthetic bacterium called the cyano bacteria these are literally green bacteria they're green because they photosynthesize and they have chlorophyll inside so these bacterium would want to move move towards light so they can optimize photosynthesis photosynthesis the process by which these photosynthetic organisms produce sugar using sunlight now recall that I said that this flatula works by rotating but there's more to the story than just that if the Flaga rotates counterclockwise counterclockwise this causes the bacterium to move in a straight line This is known as a run so think about this if the flatula rotates counterclockwise the bacteria runs it moves in a straight line if it then switches from turning counterclockwise and it turns the other way to to to clockwise this will cause the bacterium to Tumble so the flatulum reverses Direction causing the cell to stop and change course this causes a tumble so flatula can either rotate counterclockwise for runs or clockwise for tumbles so here you can see this would be the typical way that a bacterium moves through substance let's say there is some kind of attractant here on the right side side and the bacteria starts here on the left side notice that the bacteria could run in this straight line that's because the flatula is moving counterclockwise and then when the bacteria switches to clockwise rotation there'll be a tumble where the where the bacterium tumbles around picking a new Direction and then swims clock and then uh swims uh straight because of a counterclockwise rotation and then that's a run and then another tumble because of clockwise rotation and then another run and then another tumble and a run and a tumble and a run so because of this bacterium are known uh flagellated bacterium are known to exhibit what is known as run and Tumble motility the flatula results in the uh bacterium running and tumbling running and tumbling every time there's a tumbling event the bacterium can change directions and every time there's a run it moves straight so this is kind of weird because sometimes look here sometimes it looks like the bacterium is running away from the attractant remember the attractant is on the right but it'll figure out that it's moving the wrong way and it'll eventually course correct and move its way towards the attractant so bacterium you know when you look at Living bacterium under the microscope um when they're swimming around it may look chaotic but they will eventually get to the source of the the chemical that they enjoy you know they will get to the source of that sugar or that glucose but uh it's a chaotic it's a chaotic Journey there's a series of runs and tumbles um but overall the bacterium will make their way towards that chemoattractant through positive chemot taxes so now we have touched on flatula right this is a motility Associated appendage but what about the axial filament what in the world is an axial filament let's touch on that next so an axial filament also provides motility but this axial filament is very strange it's it has to do with flatula but not in the way you might think let me show you something look at this right here this cell has flatulum but those flatulum are wrapped around the body of the bacterium notice this normally when you think of a flatulum what do you think of you think of a long whip like tail outside of the cell right but imagine if instead of the flatulum being this long whip-like tail outside of the body imagine if the flatulum was was inside the the cell wall and wrapped around your body instead right so you have the flatulum wrapped around your body and the flatulum is not hanging out it's inside of the cell wall so look at this here you have these flatulum that are wrapped around the body of this bacterium and look that th those flatulum are known as periplasmic flagellum these flatulum are wrapped around the actual cell inside of the cell wall right near the cell wall now what does that uh what does that cause imagine this so again look at this imagine if the fagula instead of being a long whip-like structure outside it's wrapped around my body so when it spins what does it spin when the flatula spins what does it do look at this so this is my best explanation right when the flatula spins it also spins meat right you know look at this the flula spins me and so this is really cool it imparts a twisting or flexing motion to the cell usually you see this with spoets you know like Spiral shaped bacterium and when the flatulum work they twist the body of the cell so think imagine if you're a spirro imagine if you're a spiral-shaped bacterium and then this axio filament is causing the cell to spin right then you can cork screw you can cork screw through mucus it's called cork screw motility isn't that neat so a lot of times these spirillum shape or spirro shaped bacterium that are kind of like cork screw shaped they'll have an axial f filament so they would they're they're cork screw shape because they will literally cork screw the through the medium through the mucus that they live in isn't that interesting so when you think of axial filament think of cork screw motility all right to keep track we've talked about fagula and axial filaments which provide motility now we're moving on to appendages that have other functions we're talking about Bim and and pilli in particular these provide attachment points or form channels let's talk about the fim first all right focusing on the fimbria first the singular is fmria and the plural are fim e fim e provide adhesion but not Locomotion these are structures that allow the bacterium to adhere to various surfaces es that means attached to various surfaces so for instance I told you about plaque right I told you about the bacterium that can attach to your teeth well your tooth is pretty smooth right your tooth is nice smooth enamel so how are these fla How are these um how are these bacterium attaching to your teeth well sometimes they can use their fim their fime are these short bristle like structures that allow the bacterium to adhere to the tooth surface for instance let me show you what the fimbria look like you see here this is an electron micrograph of various bacterium and these short bristle like structures are not flatulum they're much shorter than flatulum these structures are fim and they look like little bristles and they look like kind of like Burrs you know like plant Burrs and that's for a good reason they are very sticky just like a plant Burr you know if you've ever been out in the wilderness and you picked up a bunch of Burrs um and they've stuck to your socks or to your pants you know what I'm talking about um well fime are very similar to birds on Plants they allow the bacterium to stick to a variety of surfaces all right the last one we're going to talk about an appendage that has to do with forming a channel this is known as the pilei now there are various types of pil but we're going to talk about specifically the sex pilus so what is a pilus the plural of pyus is pilei pilei provide adhesion but not Locomotion and the one we're going to talk about again is called The Sex pile pus the sex pilus is a long rigid tubular structure made of pyin protein forming the sex pilus now imagine a hollow tube of protein that one bacterium let's say this bacterium right here at the bottom here imagine this bacterium could make a hollow protein tube that extends extends extends and then it docks onto an adjacent bacterium it attaches to another bacterium close by and this bacterium could be the same species or even a different species than the one who made the sex pilus uh so so think of a hollow tube that extends from one bacterium and attaches to another this process is known as conjugation after the conjugation occurs after the sex pilus has docked onto a neighbor there is a partial transfer of DNA from one cell to another the donor cell the cell that made the sex pilus it's the only one that sends genetic information genes to the other cell imagine that so you make a hollow tube let me zoom in here you make a hollow tube tube that docks onto a neighbor that neighbor may or may not be of your same species of bacterium you then send that neighbor genes you can send that neighbor various genes you can send that neighbor plasmids you could send that neighbor genomic DNA you could send that neighbor all kinds of genes and this is known as horizontal Gene transfer this is a a lot different than how humans share genes right how do we share genes how do we pass on our genes well after mating we have fertile offspring we have an offspring a child and this is known as vertical Gene transfer because you're sharing your chromosomes with your child right so animals undergo vertical Gene transfer they pass on their genes to their offspring however bacterium they don't have parents right bacterium divide by asexual reproduction one cell simply divides into two via a process known as binary fision so how do bacteria share genes how how do bacteria share genetic information well they can form the sex pilus uh undergo conjugation transfer genes from the donor cell to the recipient cell isn't that neat and then that recipient might pick up some important genes some helpful genes like antibiotic resistance genes or toxin genes or even genes that are required for making their own sex pilus isn't that neat so you see why that's called horizontal Gene transfer because one fully developed bacterium sends genetic information to another fully developed bacterium that's a lot different than vertical Gene transfer where the genes are transferred from parent to child now let's talk about a few surface Coatings that procaryotes exhibit these surface codings are you know outside of the cell wall of these bacterium and archa they can have surface Coatings and again not all bacterium have a surface coating not all archa have surface Coatings but let's talk about what these surface Coatings are the two types we're going to discuss are s layers and glyx or glyco calices S layers are thousands of copies of a single protein linked together outside of the cell when a bacterium or an archa has an S layer this provides them with protection from the environment and it's only produced in hostile environments so you typically see organisms that have an S layer these are organisms that exist in hostile environments I feel like I have a guest here check it out it's a wicket hi Wicket Wicket have you come to say hi to your adoring fans do you want up in the cabinet watch this you guys he'll probably go up in the cabinet and sleep in there I don't know if you guys have ever seen my cabinet open but sometimes Wicket likes to go up there and Nest his nickname is wiki wiki obviously short for Wicked May he's contemplating it I can tell what are you doing Wick it go up in your cabinet go on buddy this is so good we have a visit from Wicket I have to take a break this is our break time with Wicket so Wicket he's the one with the spot on his nose he's a fun little cat he's motivated by food he enjoys yummy food Gizmo's over there in his bed Wicket apparently has left us Wicket has gone to bed all right well let's continue on that was a nice little break time with Wicket today so again s layers are usually found on organisms that live in hosle environment so a lot of times you'll find these SL layer surface coatings on Ara bacteria they're more likely to have what's known as a glyx repeating polysaccharide that means sugar subunits that may or may not include protein some bacteria might have a slime layer which is a Loosely uh it's loosely associated with the cell wall some bacterium have what's known as a capsule which is more tightly associated with the cell wall here you can see the difference between a slime layer look how loose it is to the cell wall the cell wall being in in lilac here and a capsule which is a glyco kilix that's more tightly associated with the cell wall now a a a slime layer it serves to protect the cell from loss of water and nutrients it can also a Aid in attachment slime layers can Aid in attachment to surfaces a capsule on the other hand a capsule is formed by many pathogenic bacteria these bacteria are protected against your fosic white blood cells these are the white blood cells that are tasked with finding bacteria in your body and destroying them imagine if you're covered in goo imagine if you're covered in Sugar well if you're covered in sugar and you find your way into my body my white blood cells might get confused by that Sugar layer right so bacteria that have a capsule my white blood cells have a tough time identifying that bacterium as foreign and destroying it isn't that neat so this is why several uh highly pathogenic bacterium are the ones that are capsulated because they my immune my immune system has a hard time identifying those cells as foreign isn't that neat it's like a cloaking mechanism and if you've ever seen a capsule stain you would know that with a capsule stain you can see decapsulated bacterium because in a capsule stain the basic dye stains the cell and the acidic dye stains the glass but the capsule remains unstained because the capsule is non iic which means it doesn't have a charge anything that doesn't have a charge is not going to be stained by a basic dye nor will it be stained with an acidic dye so if you see bacterium with a Halo that suggests that the bacterium has a capsule if you do a capsule stain isn't that neat so a capsule stain will allow you to identify capsulated bacterium and it's those capsulated bacterium that confuse your white blood cells that prevent your macrofagos dendritic cells or neutrophils these phagocytic white blood cells from identifying them as foreign and and destroying them now we've talked about appendages we've talked about these layers outside of the cell let's go closer to the cell and talk about the cell envelope the cell envelope is composed of two or three basic layers this includes the cytoplasmic membrane remember all cells have a cytoplasmic membrane most bacteria have a cell wall that cell wall is made up of a component called peptidoglycan peptidoglycan makes up the cell wall and then some bacterium have an outer membrane as well the gram negative bacterium have an outer membrane this is known as the cell envelope you have the cell wall the cytoplasmic membrane and in gram negative bacterium you also have an outer membrane and together this cell envelope acts as a single protective unit now let's talk about the cell wall of bacteria some bacterium have this style of cell wall they have their plasma membrane down here and outside of that they have this thick layer of this component called peptido glycan I'm going to explain what pepti glycan looks like in a minute but you should understand that peptidoglycan makes up the cell wall of bacteria and in a gram positive bacteria the peptidoglycan is very thick and that's peptidoglycan cell wall is directly outside of the plasma membrane and that's what makes up a gram positive cell wall on the other hand look at this cell wall a gram negative cell wall has a plasma membrane the cytoplasmic membrane and a very thin layer of peptidoglycan you see this is peptidoglycan It's a much thinner layer of peptidoglycan but the gram negatives in addition to having this thin layer of peptidoglycan they also have an outer membrane and outer membrane layer so instead instead of just having a single plasma membrane they have the plasma membrane a thin layer of peptidoglycan and a whole another outer membrane as well this is the key difference between what are known as the gram positive Cells versus the gram negative cells the term Graham was from the medical student H Christian Graham in his medical school residency in 188 for he developed this staining protocol that was used to differentiate between gr positive bacterium and gram negative bacterium okay the gram positive bacterium later on it was discovered that these gr positive bacterium have again this thick layer of peptidoglycan outside of their plasma membrane in addition they have these structures called lipoic acids and taic acids IDs which lend a negative charge to the cell wall these cells stain purple at the end of the Gram stain so when you do a Gram stain procedure these cells are purple conversely the gram negative cell wall remember the gram negative cell wall you have a plasma membrane a thin layer of peptidoglycan and then a whole another outer membrane on top of that and these cells stain pink these cells stain pink at the end of the Gram stain again gram positive cells stain purple and gram negative cells stain pink and I'll explain why in just a little bit but first I'm going to go into more details about the gram positive cell wall architecture versus the gram negative cell wall architecture so first of all let's talk about the cell wall itself the bacterial cell wall I said that it's made up of a component called peptido glycan and this is the component that makes up the cell wall of bacteria this is found in the cell walls of most bacteria there are some species of bacteria that lack a cell wall and those tend to be the pleomorphic bacterium remember the ones that don't have a particular cell shape but peptidal glycan makes up the cell while a bacterium by the way Pepto glycan is unique to bacteria what does that mean that means that only bacteria the domain bacteria have cell walls comprised of peptidoglycan no other domain of life has cell walls composed of uh peptidoglycan ARA do not have cell walls of peptidoglycan though they can have S layers and ukaria do not have cell walls of peptidoglycan either it is unique to bacteria and what is pepti Gan look like peptidoglycan is essentially a chain of sugars mg MGM um G stands for n AAL glucosamine and m stands for n AAL moric acid mg MGM each of these is a sugar right mainly a sugar however the M's the M's which are the N acid moric acids not only is there a sugar but there's a short peptide attached as well basically a short chain of amino acids and that short chain of amino acids can cross link to other chains of these um peptidoglycan as well so essentially what is the peptidoglycan cell wall the peptidoglycan is made up of sugars as well as short peptides each of these sugar chains you see how it's like mg MGM these sugars form spirals right they're linked together as polysaccharide spirals adjacent spirals will Crosslink to one another with these inter Bridges you see here like here is a glycine Interbridge there are also direct inter Bridges the short peptide Tails hanging off from the sugars will cross link to adjacent peptide Tails so this gives you a very strong rigid structure peptidoglycan is very strong and rigid because you have these spirals of sugars Crosslink with peptide bonds to adjacent uh spirals of sugar and that's what makes up the cell wall of bacteria now that you know what peptidal gly can is in a little bit more detail remember it's mainly sugar but also some protein in there we should take a look a closer look at the gram positive cell wall remember that the gram positive cell wall consists of the plasma membrane down here with a thick layer of peptido glycan and embedded in that thick layer of peptidoglycan are these structures called lipoic acids and just regular taic acids these taic acids lend a negative charge to the cell wall see here the functions of tyo and lipoic acids cell wall maintenance enlargement during cell division and acidic charge or negative charge on the cell wall the cell surface and that's what I want you to know about the gr positive cell wall that it has a thick layer of peptidoglycan as well as lipoic acids embedded inside now turning our attention to gram negative cell walls remember here you have a very interesting structure you have a plasma membrane of course all cells have a plasma membrane or cytoplasmic membrane outside of that you have a thin very thin layer of peptidoglycan and yet outside of that remember you have a whole Outer membrane you have a whole another membrane outside of that so it's very interesting how the architecture differs between the gram negative cell wall and the gram positive cell wall a few more things to note these large structures in the outer membrane of the gram negative cell wall these large pores are called porin porin are large pores that are formed with these porin proteins that allow substances to enter and exit the outer membrane of the cell wall additionally there are these structures in the outer membrane the outer part okay follow me on this the outer part of the outer membrane of gram negative cells you see how it's drawn in pink these little spheres are drawn in pink and you have these little Tails hanging off well these little Tails are part of what's known as lipopolysaccharides and these lipopolysaccharides exist only in the the outer part of the outer membrane of gram negative cells only and they're very important let me tell you what these lipopolysaccharides are what are these components of the outer membrane the outer part of the outer membrane of gram negative cells only this is what it looks like this is lipop poly saccharide lipopolysaccharide remember these are these are found in the outer part of the outer membrane of gram negative cells only it's a polysaccharide chain which functions as a cell marker and receptor these these structures these structures okay have a lipid portion look here this is the lipid portion of LPS it's a fat and this is the sugar portion of LPS There is the O antigen with many sugar units and the core polysaccharide with sugars here down here this is the part that embeds into the outer membrane of the gram negative cell this is known as lipid a and lipid a is a lipid it's a fat or or a lipid and it has fatty acids this is what embeds into the outer part of the outer membrane of the gram negative cell wall now what do I need you to know again I need you to know that this structure LPS it's made up of an O antigen a core polysaccharide and L lipid a it's found only in the outer part of the outer membrane of gram negative cells and something very important that you should know is that the lipid portion of this molecule is called lipid a and it is called endotoxin it's very toxic to your body if this portion of LPS the lipid a portion of LPS gets into your system it can stimulate fever and even septic shock it can lead to death so it's very toxic it's very toxic to you and me so gram negative cells are toxic due to lipid a lipid a is is a portion of that LPS which exists in the outer part of the outer membrane of gram negative cells so again when we look at these gram negative cells and we look at these pink this pink layer here with these Tails that's LPS and the lipid portion of that is toxic to you and me again for gram negatives what do I want to know I want to know with the gram negatives you have the thin uh I'm sorry you have a plasma membrane you have a thin layer of potato glycan outside of that you have an outer membrane and the outer part of the outer membrane includes LPS or lipopolysaccharides those are dangerous because the lipid portion of that lipopolysaccharide is toxic to humans and there are these large pores called porins in the outer membrane as well which allow for things to enter and exit the cell with ease now again most bacteria have have either a gram positive cell wall architecture or a gram negative cell wall architecture but there are some non-typical cell walls so for instance there are bacterium that lack cell wall structure and those are the pom morphic bacterium and then there are there bacterium that have these molic acids in the cell wall molic acids also known as cord Factor these are waxy structures in the membrane of the cell in the in the cell wall of the cell and this is a very longchain fatty acid this is what makes the uh molic acids waxy it in it contributes to the pathogenicity of these organisms they tend to be disease-causing and these are known as the acid fast bacterium so remember in the lab we conduct a acid fast stain those acid fast bacterium are the ones that have molic acids in the cell wall these bacterium tend to be pathogenic disease-causing so for instance the bacterium that cause tuberculosis and leprosy these are bacterium with molic acids in the cell wall these are acid fast bacterium and as I mentioned before although most bacterium are either gram positive or gram negative some some bacterium naturally lack a cell wall they don't have a cell wall at all for instance the microplasmas are an example of such organism they're bacterium that lack a cell wall so these bacterium don't have a particular shape look at this example here in this image notice that each of these micro bacterium has a different shape and that's because they don't have a particular cell wall and if you if you don't have a cell wall you're not going to have a specific cell shape so what are the functions of the cytoplasmic membrane you know the membrane of the cell in bacteria not only is the cell membrane selectively permeable which means you allow nutrients to enter the cell and waste to exit the cell but you also have energy reactions this means that ATP is produced at the cell membrane you know how your mitochondria produces ATP using an electron transport chain and ATP synthes well in bacteria that stuff is done in the cell membrane there's an electron transport chain and ATP synthes in the plasma membrane in the cell membrane obviously there are numerous electron transport chains and ATP synthes synthesis however that's where ATP p is made at the plasma membrane so what do we have to keep in mind when we're thinking about G positive versus gram negative bacterium the outer membrane in gram negative bacterium makes them more resistant to certain antibiotics or antimicrobial chemicals the gram negative bacteria it's more difficult to inhibit or kill than gr positive bacteria gr positive bacteria tend to be a little easier to treat easier to kill off if they cause an infection infections with gr positive bacteria are treated differently than infections with gram negative bacteria so it's important to determine whether your infection is caused by a gram positive bacteria or gram negative bacteria because the treatment options are different and the best course of action the best course of treatment may be different now let's quickly go through the Gram stain and determine and how it works remember the first step of the Gram stain is to add Crystal Violet a basic die remember that basic dyes have a positive charge and Crystal Violet is a basic Dy with a positive charge this means that Crystal Violet will stick to the negatively charged cell and Crystal Violet will stick to not only gr positive cells on the left but gram negative cells on the right as well remember that a gr positive cell wall has a you know a gram positive cell has a thick peptidoglycan cell wall and a gram negative cell has a thin peptidoglycan cell wall both cells are stained purple at the first step with Crystal Violet next grams iodine is added as a Morant you should know that Morant are substances that keep a dye in place when you add GRS iodine it complexes with the crystal Violet it complexes with the peptidoglycan mesh work and with Crystal Violet and so it makes the dye thicker imagine if this is Crystal Violet iodine will complex with Crystal Violet forming a diiodine complex that makes the iodine stay in place with the crystal Violet that makes that Crystal Violet die stay in place it makes the crystal Violet less permeable in the cell it prevents the crystal Violet from leaving the cell membrane as easily or as leaving the cell wall as easily so at this point both cells both gram positive and gram negative cells will be purple next we conduct what's known as the alcohol step this is the decolorizer step remember we add acetone alcohol acetone alcohol decolorizes the cells however when you add the acetone alcohol remember you do it in a dropwise fashion at an angle for only 8 to 10 seconds this allows only the gram negative cells to clear of I of the color of the crystal Violet iodine complex the gram positives retain that color and so if you do it right you've cleared the gram negative cells with the uh Crystal Violet but the gr positive cells retain Crystal Violet and are still purple remember you could mess up this step pretty easily if you Dain too much both the gram positive and the gram negative cells will appear clear if you don't Dain enough both the gram positive and the gram negative cells will remain purple so you need to destain just right kind of like Goldilocks you need to Dain in such a fashion that the gr negative cells become clear but the gr positive cells retain the purple color next so at this point again at this point the gram positive cells appear purple the gr negative cells should appear clear now we could take a look at these cells under the microscope but it would be hard to see the gr negative cells so we're going to add a counter stain the counter stain also known as the secondary stain is a stain known as saffrin saffrin is a red dye and saffrin is going to stain all the cells it's going to stain the gram negative cells pink it's also going to stay in the gram positive cells but because it's so much lighter than the purple color that's already in the gram positive cells it's not going to be noticeable so at this point your gram positive cells should appear purple Under the microscope and your Gram negative cells should appear pink Under the microscope and that's how the Graham stain procedure works okay so we add add the again we add the crystal Violet it stains both gram positives and gram negatives we add the iodine as a Morant which keeps the Dy in place we add the decolorizer acetone alcohol and if you if you add it in the right amount at the right amount of time you will wash out the gram negative cells but not the gram positives and lastly we will you know use the counter stain to show the the gram negative cells as pink and this is why at the end of Hans Christian grams uh gram stained procedure gram positives end up purple and gram negatives end up pink so at this point we've talked about all of the structures outside of the bacterial cell what about inside of the bacterial cell let's talk about the inside of the bacterial cell starting with cytoplasm cytoplasm refers to the gelat solution contained by a cytoplasmic membrane it's all of the solution inside of the cell which is mainly made up of water um it's about 70 to 80% water and it's the predominant site for the cell's biochemical and synthetic activities this cytoplasm uh you know I refer to it as the fluid inside of the cell but it's a complex mixture of sugars amino acids and salts there's also Al a chromatin body you know this uh there's the nucleoid there are ribosomes floating around in the cytoplasm granules and fibers here you can see the bacterial chromosomes inside of the cell remember that that bacteria have chromosomes and not plural but a single circular chromosome bacteria have a single circular strand of double strand DNA and that DNA exists as a tightly coiled uh complex inside of the cell known as the nucleoid the nucleoid there can also be extra chromosomal or non-chromosomal DNA inside a bacteria known as plasmids plasmids are not part of the normal chromosome of the cell these are non-essential pieces of DNA they're separate double stranded Circles of DNA they're small they're small circularized dnas but they can actually have important genes they can have important genes that give certain traits to the cell such as antibiotic resistance genes or toxin genes or even genes that allow the bacterium to form a sex pilus bacteria also have ribosomes and this is something interesting ribosomes are the organel responsible for synthesizing proteins the the ribosome synthesizes proteins in fact the ribosome is made up of RNA and protein now what's interesting and what you should know is that the bacterial ribosomes are actually smaller than the eukaryotic ribosomes bacterial ribosomes are known as 70s ribosomes whereas UK carotic ribosomes are known as 8 s ribosomes s stands for Swedberg orberg units this is how fast a substance travels through a centrifuge okay so it has to do with centrifugation bacteria have smaller uh ribosomes than UK carots um but that doesn't mean they don't do the same function ribosomes function the same ribosomes function to syn syze proteins that's what ribosomes do they make proteins bacterial ribosomes make proteins eukaryotic ribosomes make proteins however the size and the shape vary and remember what does a ribosome look like ribosomes have a large subunit and a small subunit and those two subunits can come together I call it a hamburger bun Arrangement right the hamburger bun you've got the large bun and the small bun they can come together they can come apart in bacteria the large subunit is called the 50s subunit and the small subunit is called the 30s subunit together the 50s and the 30s subunits comprise the 70s ribosome in bacteria you also have structures called inclusion bodies inclusion bodies are storage sites for nutrients during periods of abundance so let's say that the bacterium finds a source of phosphate right phosphates pretty important nutrient for the cell it can form a little inclusion body which is a storage site in inside of the bacterium for phosphate and it can make these inclusions for various types of nutrients in periods of abundance now some bacteria can form what are known as endospores and these are some dangerous bacterium these are bacterium that can form these highly defensive structures called endospores these defensive uh seeds you can think of them as seeds endospores can withstand hostile conditions and facilitate survival and there are basically two genuses of bacterium that can form endospores you should know that the two genus the two genuses of of bacteria that can form endos spores are the genus claustrum and the genus basilis those two genuses of bacterium can form endospores and when endospores are formed the vegetative cell which is the you know the it's also known as the mother cell this is the metabolically active cell the vegetative cell will form the endospore through a process known as sporulation the endospore is the inert resting condition it is a dormant seed and it is highly resistant to the environment and the process by which the vegetative or Mother cell will form the endospore is called sporulation sporulation refers to Spore formation and this can be induced by environmental conditions this is a endospore on the right see how it looks like a seed the the endospore can resist heat you know not not to an infinite degree you know autoclaves can still destroy and endospore fire can still destroy an endospore but it's resistant to high levels of heat for instance endospores are resistant to Boiling conditions endospores are resistant to drying out or what's known as desiccation drying out or desiccation endospores are resistant to free freezing conditions they're resistant to some level of radiation for example UV radiation they're resistant to chemicals many chemicals not all chemicals but most chemicals these little seeds this little endospores are highly highly resistant to the environment and what causes the endospore to form usually it's a depletion of nutrients so nutrients dip there is a depletion of nutrients especially carbon and nitrogen sources if these bacterium remember only the bacterium in the genus clostridium or the genus bacillus if these bacterium are lacking in these carbon sources or nitrogen sources they can undergo endospore formation the Mother cell will form endospores the vegetative cell will form endospores and this refers to the sporangium the sporangium refers to the sporulating cell the cell that's making the Spore and transformation can take 6 to8 hours in most species so it could take 6 to 8 hours for these endospores to form here's the process by which sporulation occurs it's called the sporulation cycle so let's go ahead and start from the beginning in Step One in step one you can see the vegetative or Mother cell begins to be depleted of nutrients this is a this is the vegetative or Mother cell somehow it's being depleted of nutrients so there aren't many nutrients around there's not not good food there's no good source of sugar or food in the environment so what happens is this triggers sporulation notice that this Mother cell has its chromosome this is its nucleoid it has a cytoplasm in yellow it has a cytoplasmic membrane in yellow in pink or purple it has the cell wall but it's going to trigger sporulation so at at this point it's going to uh copy the chromosome the chromosome or nucleoid is duplicated and separated next a membrane forms around What's called the for Spore the for Spore is going to become the endospore so you have a copy of the chromosome inside of a membrane next the sporangium engulfs the forcebore for further development this membrane this membrane engulfs this other Force Spore so you end up with two membranes two membranes surrounding the early endospore the sporangium begins to actively synthesize endospore layers around the forespore so there are endospores layers forming around the forespore next a cortex forms a cortex forms around the four Spore what's a cortex it's made up of pept glycan remember pept glycan is that sugary proteinaceous stuff that makes up the cell wall a bacteria so imagine this is the for Spore it's DNA surrounded by the plasma membrane and a cortex the cortex is made of peptidoglycan then the mature endospore form so the endospores maturing and by the way at this point the this other copy of the DNA gets degraded next um other protein layers can actually form on the endospore as well such as What's called the endospore coat and the exosporium these are additional layers on top of the endospore that makes it more resistant the endospore can then lice out of the cell it can leave the cell and when good conditions return When favorable conditions and nutrients return the endospore can germinate releasing the new vegetative cell to start the cycle over again and again this is known as the typical sporulation cycle in a basilis species in a spor forer and again what triggers germination of the endospore this means that the endospore will grow out it will uh germinate it will hatch if you will allowing a new vegetative cell to grow out from the endospore this occurs when there's exposure to water and a germination agent a germination agent stimulates the formation of hydrolytic enzymes these are enzymes that will break down that cortex remember the cortex is peptidoglycan and then that core can rehydrate taking up nutrients and the bacterium will grow out from the endospore a vegetative cell will form again this can occur in about an hour and a half so again when good conditions moist and nutrient Rich conditions return those dormant endospores can germinate and grow out to form vegetative mother cells again and again remember it's the genus basilis and the genus clostridium that are capable of making endospores only those two genus of bacterium so for instance basilis andthis the cause positive agent of Anthrax is a endospore forer clostridium tetani which causes tetanus or lock jaw is an endospore former clostridium perenin which causes gas Gang Green is a endospore former clostridium botulinum which causes botulism is an endospore former and clostridium defil which we talked about is SE diff you know that that uh gut bacterium that causes colitis and bloody diarrhea this is an endospore forer notice that all of these start with um claustrum or basilis let's ask let's ask Wicked a question we haven't asked him a question in this video so would eoli be an endospore former oh that's right wake it eoli is not an endospore forer because e stands for eishia and eishia is not the right genus only basilis and clostridium make endospores so would uh staf cacus orius make endospores Wicket no that's right again again staf cacus Arius would not make endospores because it's not in the genus bacillus or claustrum would streptococus pyogenes make endospores again no because those that's not in the genus basilis or costum it's only the genus clostridium or basilis that make those endospores and again in the medical field in the clinic endospores are a problem they are constant Intruders where sterility and cleanliness are important it's the reason why we autoclave our surgical instruments or in the dental office we autoclave the dental equipment we cannot just boil water to to destroy endospores we cannot use soap or regular disinfectants to destroy endospores we need to autoclave the instruments to to destroy endospores we have to help protect against endospores entering wounds because this can cause infection in the food canning industry we have to prevent endospores from entering canned foods because that can cause uh the contamin ation right in the last part of this chapter we're discussing archa remember ARA are procaryotic organisms as well in the domain archa however ARA are usually not studied deeply in microbiology courses and that's because archa are not known for causing many you know diseases in humans remember one thing ARA are more closely related to The Domain ukaria than they are to The Domain bacteria we discussed that before you should realize that ARA do not have cell walls of peptidoglycan remember peptidoglycan cell walls are unique to The Domain bacteria most ARA live in habitats that are extreme for instance high or low heat very salty environments acidic or basic environments High Press environments and and low atmosphere environments and lastly let's talk about what a species is in a bacterial sense so when we're talking about a bacterial or archal species we can't refer or Define a species the same way as we Define species and animals in animals a species includes a population that can interbreed and have fertile offspring but remember in bacteria there's no breeding and there's no forming Offspring due to breeding there's no sexual reproduction so in bacteria we can't Define a species the same way as we Define species in animals so because of that we need to have a different definition of species so a bacterial species is defined as a collection of cells where a bacterial cells where which share an overall pattern of similar traits so for instance what do we mean by similar traits so for instance a trait might be the ability to break down lactose the ability to break down hydrogen peroxide uh the presence of a gr positive cell wall the presence of a capsule the presence of flatulum um all of these are traits so when you have bacterium that share the same traits once they share enough traits you can categorize them as the same species now if that's what a species is what is a subspecies or a strain or type these are bacteria of the same species that have differing characteristics so for instance there is a strain of eoli that is capable of making a potent toxin called the Shiga toxin which it got from the shagel bacterium right and this shot toxin makes that strain of eoli much more dangerous it's the 0157 H7 strain of ecoli this strain of ecoli is more dangerous than your normal everyday ecoli because it picked up an extra Gene from another um bacterium right so that would be a dangerous pathogenic strain of eoli you see how um a strain would be a member of the same species but having different characteristics like the ability to let's say produce a toxin or the ability to I don't know be U resistant to a particular antibiotic and that's it that leads to the end of the chapter thank you for joining me in the chapter 4 of this course um hopefully you learned a lot let me know in the comment box below if you have any questions about this chapter and I will catch you guys in the next one Dr D Dr D Dr D Dr D Dr D D Dr D A Dr D Dr D Dr D Dr D Dr D Dr D A Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D