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5. Genetics of Bacteria and Viruses

Working with Microorganisms


Bacteria in the Laboratory

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Hi in this video I'm gonna be talking about working with microorganisms. So we work with microorganisms in a laboratory setting because they're easy to work with right there fast dividing they take up little space. You can easily grow them. You can easily cause mutations in them. And so bacteria are often used to study various types of genetics in lambs. So how do they do this? Well the first thing that they do is a process called plating. And this is how you actually grow the bacteria. So you take some bacteria. It's usually a lab strain of e. Coli which means that um it's not dangerous. You know you hear of the coli and it causes all sorts of illnesses with the lab strain has been made so that it's not going to get you sick. Um So the plating is when you put the bacteria in some kind of culture is what it's called. It's culture is any kind of place where you grow the bacteria. It could be a plated culture. It can be liquid culture but you're just growing this bacteria you're culturing them to get more of them. And when you play you actually take that liquid culture where the bacteria has been growing and you put it onto a Petri dish containing a substance called agar. Which is kind of like a very firm jello you may have you can use it you can actually eat it if it's not used for bacteria. Um So you may have had it before but I don't think it tastes that good. So I don't really eat it but it's just kind of if you've never seen it's kind of like a very firm jello type thing. And so the cells when they're plated they'll divide right there bacteria. They're fast dividing. They'll keep growing but they don't move around, they stay in that spot where they are originally plated wherever they sat down and were plated. And so what happens is that they're dividing but they're not moving. So that means that all these cells just keep dividing on top of each other and it grows and grows and grows and eventually becomes this clump of cells we call this clump of cells the colony And this colony actually can be seen with the eye when there's you know 10 to the seventh bacteria there. And um generally these clones are very interesting because bacteria divide a sexually and so these clones actually are derived from a single genetic ancestor, meaning that they all have the same genetics. And so that allows you to get a lot of bacteria which all have the same genetics and genome. Um And it's it's great for studying now. There's two types of classifications on what the bacteria need to grow. There's the pro to trophic and this is pretty much generally like wild type right? So they grow on this substance called minimal media. It contains salt, it contains car, it contains water you know just basic nutrients for bacteria but they don't need anything special. They're the wild type ones essentially. And what you'll see is you'll see them written with the plus sign and this is a common thing that we've seen before. So that's good. Then you have the oxygen trophic bacteria and these have to have one or more specific nutrients present so they can't just survive on this minimal media. They have to have known what's called this complete media and the complete media has something extra. So something that they're lacking. Now usually these are mutants because the mutation is going to mean that that bacteria can't produce something it needs. So you have to give it to it in the media. So the mutant is generally written with the minus sign And this is something we're familiar with from the other genetics things. So here's an example of a bacterial plate. You can see that there's streaks here and all of this is bacteria. Here's an individual colony. You can see there's a bunch here they started growing together these circles here are individual colonies. So these are one bacterium was plated here and it kept growing and growing and growing and all these cells just kept growing on top of it. And now it's finally big enough where you can actually just see it with your eyes and these are it's very likely um pretty much almost certain that they are genetic copies of each other unless some kind of weird mutation has happened. These are genetic copies of each other. So they're clones now bacterial DNA. Let's talk about that for a second. So the bacterial chromosome is the main D. N. A. Molecule in the bacterium. Okay so that's what um you you know that's where the bacteria gets all of its genes that you everything that makes it live survive grow replicate divide et cetera. Right? Those are the essential genes that are found in that bacteria. But bacteria also have a second source of D. N. A. And this is called a plasma. And plasma is a small circular D. N. A. And it sounded bacteria and it's in addition to an outside of the main chromosome. So this plasma has nothing to do with the main chromosome. Right? And the genes that it contains are non essential to bacteria function. So if the plasma wasn't there the bacteria could still survive but if it is there it adds a little bit of extra you know uniqueness to that bacteria that can allow it to do things that it wouldn't be able to do. Otherwise. You can imagine how that is beneficial to that bacteria. And so these plasmids, there's a ton of them. So e coli has 270 different types that it can have. You can imagine all those different combinations of those plasmids can also um cause different uh fanatic effects help it live in environments it wouldn't otherwise help it become antibiotic resistant is a good example. So these plasmas are super important for bacterial evolution and survival even though they're not technically required for just bacterial living. And so um like in anything else if you have a mutation in the bacterial D. N. A. It shows this often a typically so typically how scientists will look at this is they say okay well how is the colony affected? Right because that's what they can actually see with the naked eye. So it'll affect colony morphology. Um So that's that shape or size or its edges can be rough or smooth. Um It causes antibiotic resistance which is a big thing in medicine but also very much manipulated by scientists um to allow bacteria to grow in certain antibiotics and not in others allows you to select for the bacteria you want. Um You can create these oxen trophies are mutants, you have bacterial mutations that allow bacteria to break down different chemicals um Like oil spills and stuff. You hear about these things in the news. So bacterial D. N. A. Is super important for our existence on earth. So here's an example of what a plasma looks like. You don't at all. You need to know what any of these words are. Just see is the circular DNA. It has jeans on it represented by all these different colors and it adds something to the bacteria that it doesn't have otherwise. Now bacterial DNA can be transferred to other bacteria in three main ways. So the first one and all of these ways they're gonna have their own videos on them. But the first one I'm just gonna briefly go over is conjugation and this is D. N. A. Transfer cause between contact and fusion of two different bacterial cells. Then you have transformation. And this is when a bacterium takes up D. N. A. Found in the external environment. So so DNA just floating around in the bacteria is like DNA. Let me take that up and then you have transaction. And this is where a bacterial fage. If you remember what this is. This is a virus that transfers D. N. A. Into the bacterium. And these three are examples of horizontal transmission and this transfers DNA between individual bacteria that always already exists. Whereas everything we talked to up into this point has been talking about vertical transmission and that's transferring DNA through generation. So in this case it would be bacterial division right? The cell divides it creates that daughter cell. It's passing that um D. N. A. Vertically through its offspring. Whereas horizontal transmission there's no offspring. You know doing anything. It's just transferring it from one bacteria to another. So let me show you what this looks like. Here we have conjugation. So here's a bacterial cell and here's another and you can see a structure forms between them and that allows for the transfer of D. N. A. You have transformation where you have this D. N. A. It's just floating through the environment Not really doing anything in the bacteria comes in contact with it. It's like let me eat that so it takes it up. Then you have transaction where you have this virus which we call fage for bacteria. It has some D. N. A. Here that it's taken up somewhere. Could have taken it up in another bacteria from the environment wherever it's gotten it. And it's like I'm just gonna put that in here so it ends up in the bacteria. So these are the three different types and each one of them are gonna have their own videos because they're definitely super important. But just to understand what the differences are um is super important. So with that let's not move on.

What is a plasmid?


True or False:All bacterial cells within a bacteria colony grown on a plate in a laboratory are genetically identical.


Which of the following is NOT a way scientists can phenotypically identify a bacterial mutation?