Hi. In this video, I'm going to be talking about working with microorganisms. So, we work with microorganisms in a laboratory setting because they are easy to work with. Right? They're 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 labs.
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 it's not dangerous. Now you hear of E. coli and it causes all sorts of illnesses, well the lab strain has been made so that it's not going to get you sick. So the plating is when you put the bacteria in some kind of culture, which is what it's called. Culture is any kind of place where you grow the bacteria. It could be a plated culture, it can be a liquid culture, but you're just growing this bacteria. You're culturing them to get more of them. And when you plate, 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. 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, it's kind of like a very firm jello type thing. And so the cells, when they're plated, they'll divide, right, they're 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 a colony. And this colony actually can be seen with the eye when there are 107 bacteria there. And generally, these colonies are very interesting because bacteria divide asexually, and so, these colonies 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, and it's great for studying.
Now there are 2 types of classifications on what the bacteria need to grow. There's the prototrophic, and this is pretty much generally like wild type. Right? So they grow on a substance called minimal media. It contains salt, it contains carbon, 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 auxotrophic 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 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 a 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, you know, we're familiar with from the other genetics things.
So here's an example of a bacterial plate. You can see that there are 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, you know, 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, 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 DNA molecule in the bacterium. Okay. So that's what, you know, that's where the bacteria gets all of its genes to do everything that makes it live, survive, grow, replicate, divide, etc. Right? Those are the essential genes that are found in that bacteria. But bacterium also have a second source of DNA, and this is called a plasmid. And a plasmid is a small circular DNA and it's found in bacteria, and it's in addition to and outside of the main chromosome. So this plasmid has nothing to do with the main chromosome. Right? And the genes that it contains are non-essential to bacterial function. So if the plasmid 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 are 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 cause different phenotypic effects, help it live in environments it wouldn't otherwise, help it become antibiotic-resistant is a good example. So these plasmids are super important for bacterial evolution and survival, even though they're not technically required for just bacterial living. And so, like in anything else, if you have a mutation in the bacterial DNA, it shows this off phenotypically. 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, so that's its shape or size or its edges can be rough or smooth. It causes antibiotic resistance, which is a big thing in medicine, but also very much manipulated by scientists, to allow bacteria to grow in certain antibiotics and not others, allows you to select for the bacteria you want. You can create these auxotrophs, these are mutants. You have bacterial mutations that allow bacteria to break down different chemicals, like oil spills and stuff. You hear about these things in the news. So bacterial DNA is super important for our existence on Earth.
So here's an example of what a plasmid looks like. You don't at all need to know what any of these words are. We just see it's the circular DNA, it has genes 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 3 main ways. So the first one, and all of these ways are going to have their own videos on them, but the first one I'm just going to briefly go over is conjugation, and this is DNA transfer caused between contact and fusion of two different bacterial cells. Then you have transformation, and this is when a bacterium takes up DNA found in the external environment, so DNA just floating around in the bacteria like, oh DNA, let me take that up. And then you have transduction, and this is where a bacteriophage, if you remember what this is, this is a virus that transfers DNA into the bacterium. And these three are examples of horizontal transmission, and this transfers DNA between individual bacteria that all way already exist, whereas everything we've talked to up until 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? It the cell divides, it creates that daughter cell. It's passing that DNA 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 DNA. You have transformation where you have this DNA, it's just floating through the environment, not really doing anything, and the bacteria comes in contact with it. It's like, let me eat that, so it takes it up. Then you have transduction where you have this virus, which we call phage. For bacteria, it has some DNA here that it's taken up somewhere. It could have taken it up in another bacteria from that environment, wherever it's gotten it, and it's like I'm just going to put that in here. So it ends up in the bacteria. So these are the three different types, and each one of them is going to have their own videos because they're definitely super important. But just to understand what the differences are, is super important. So, with that, let's now move on.
