Bacterial Conjugation

Hi in this video, I'm gonna be talking about bacterial conjugation. So conjugation is the physical union of bacterial cells. Or two bacterial cells come together, they actually fuse in part and during this fusion they exchange genetic material. So this was first discovered in 1946 by the scientists. Uh I'm not gonna butcher butcher these names but Leader Bergen and Tatum. So what they did is they had a coli and they had two strains of a coli, we're just gonna call them straight A. And strain B. Now strain A only grows in media that contains this these two components. You don't need to memorize these two components. Just sort of understand the concept. So strain A could only grow if there was the certain materials available string B. Could only grow in medium with certain materials but it was different. So it requires three things uh these amino acids here. Um and chemical um that strain A. Didn't right? So they had these two strings and they both needed different very specific things to grow. So they mix them. They said let's mix these two strains. So we have this tube, we put strain A in there, we put strength be in there and we plate them onto a surface and on this surface contains none of the materials that they need to grow, right? So it doesn't contain anything that strain A. Needs and it doesn't contain anything that strain B. Needs. So these cells should not grow at all because because it doesn't have the nutrients that either of these strains need to grow. But what happened? So they were expecting to have a completely blank plate. Nothing was supposed to grow. But what happened was actually that some cells grew. And so they were like how in the world did this happen? And so they hypothesized that what happened was that the strains actually exchange D. N. A. So um so strange A. Was wild type or essentially could grow without the presence of these. And strain B. Could grow without the presence of these. So they exchanged the D. N. A. That allowed each one to grow independent of the others chemicals. So strange A. Um gave the ability to grow without losing. For instance String eight doesn't need losing to grow right it's what it is here. So it donated that gene to string B. And then now strain B. Is like okay I can grow without losing. And it did that for each one of these genes that was preventing these things from growing and allowed them to grow. So it exchanged that DNA between the two strains. And so um that allowed them to grow. Now I'm gonna talk more about how this has happened and what's actually being exchanged. But first I want to talk a little bit about some of the structures. So the sex pill A. Or the F. Pillai depending on the book that you're using is the name of the structure that actually allow those bacteria to come together for conjugation. And then the bridge that's formed between them. There's a conjugation bridge and that's actually the passageways. It acts exactly like a bridge that allows the DNA to cross from one bacteria to another. And I'll show you images of these in future videos. But let me go over this experiment. So you have bacterial strain A. Here it is and it grows in condition A. You have bacterial be it grows in condition B. If you have A. And B. And no conjugation then it's not gonna grow when it does not have either of these things. So A. B. Negative. It's lacking A. And B. But if you have conjugation then it will still grow because that D. N. A. Is being transferred between the two. So that was the main experiment that discovered bacterial conjugation. So with that let's move on.

Okay so now let's talk about the F. Factor. So what is the F. Factor? Well the F factor is what allows bacteria to swap DNA. So what allows the bacteria to undergo conjugation. So if bacteria contained the F. Factor we say that their F. Plus and that allows them to donate genetic material while bacteria that don't have it we say how are F minus and they can only accept genetic material. So not every bacteria can like initiate that conjugation. Only bacteria with the F. Factor can. So what is the F. Factor? It's a plasma. So remember what a plasma is? It's that circular DNA. That exists outside of the main chromosome. It's not necessary for bacteria survival. But it does give it certain advantages. So this F factor is a plasma that allows bacteria to undergo conjugation which is a huge advantage because that allows for more genetic diversity. Which is always a good thing. Now the F factor can actually be given to an sl without it. So an F minus sell through conjugation And as well as other DNA. As well. Right that's conjugation. But it's important to realize that the bacterial that's accepting that D. N. A. From the F. Factor plasma is doing so through conjugation. So it's becoming this recombination it's becoming um it has different DNA. Than what it started with. It's sort of a mix now between the two bacteria. So we call it over competent. But this is a competent via conjugation and not genetic recombination. And you may say duh of course it's conjugation donating this D. N. A. It's not undergoing crossing over? It's not you know the bacterial chromosomes aren't lining up and doing anything. Why are you even telling me this? Obviously that's the case. So the reason I'm telling you this is because it's gonna get confusing on the next page. Um with something that's kind of a derivative of the F factor. So I really wanted to get the point across that. It's the F. Plus factor as a plasmid that it happens through conjugation and not genetic recombination. So if we scroll down and look at what this looks like we have bacterial cell one this is a donor bacterial cell to this is a recipient. So if I were to label F plus an F minus which one would be plus and which one would be minus. Right. The donor would be the F plus because it's donating. It has that f plasma and the recipient would be F minus because it doesn't. And so here's the f plasma here. You can see that this allows the donor to create the structure called the pill. I. And that structure allows for the conjugation of the two bacterial cells. You can see that it fuses and this is starting to go into the other cell and at the end you end up with two cells with the F plus plasma. The f factor. Now you may ask, okay well if it donated that F factor, how come it still has it? Right? Like it gave it away. So shouldn't it be F minus Now? The reason it's not the main reason that it's not is because usually these cells contain multiple copies of the F factor. So if it has 30 copies, right? You know I didn't draw it here for space but if it has 30 copies and it gets one away, it's still about 29. Right, it's still an positive. Um so so it's it's not just completely getting rid of it. It's just spreading that a factor around the second way is more rare and it actually occurs through replication at this point where it uses that F factor as a template to actually just make a copy of it in the in the recipient cell. Um But this is again like I said, it's a it's a rare form of what happens most of the time. What happens is that there's multiple copies and it gives one away. Now here we get to a little bit of confusion because there's a second type of cell called the HFR. Or the high frequency of recombination bacteria. Now these bacteria have the F factor but it is not a plasma. So at some point in this bacterial genetic history it had the F factor as a plasma but it's somehow something you know started it and it became actually integrated into that main chromosome. So it lost the plasma. It no longer has it as a plasma but instead it has it as a linear gene found in the chromosome. So now it's in the main part of the D. N. A. It's actually a gene. It's linear. It's completely different than the F. Factor but it has the same function. Right? The F factor allows that bacteria to donate D. N. A. So if it doesn't have a plasma to donate well but it's in the bacterial chromosome it still wants to donate D. N. A. But if it's in the chromosome it can't just give a copy of it away. That's not how this works. Instead what happens it has to happen through genetic recombination. Remember? And this is why I was telling you about how if it's a plasma it's going through conjugation. But if it's the F. The H. F. R. And it's actually incorporated into the chromosome the F. Plus can't be given to the F minus via conjugation because it can't just give its chromosome away or else it'll diet needs that chromosome for life. So um how it does is it can still make the competence. It can still make f. Positive cells but it has to do so through recombination instead of this conjugation. So what this looks like I'm not gonna go through the whole picture. But you can see here that instead of having it in a plasma form which is a circular form. Here's this bacterial chromosome and you can see it's actually a linear jean here in blue is the HFR and it still allows it to have this pill i it still can initiate conjugation. But instead of just giving that whole chromosome over to the other cell it actually just re combines and makes a bunch of competence. So it has a high frequency of recombination because it wants to donate that D. N. A. It has the F. Factor but it can't. So the only thing it can do is create those combinations. Whereas if if it's a plasma and its separate then it can undergo this normal conjugation and actually give its plasma away. But the HFR bacteria actually really useful. Almost even more useful than the F. Plus bacteria at least in terms of humans. Because we can use this H. F. R. Bacteria to map bacterial chromosomes. Now remember the H. F. R. Is a linear gene is found inside the bacterial chromosome. And so how you would do this is you take an HFR cell and an F minus bacterial cell. So this has the F. Factor linear and this doesn't. So the HFR will stimulate the bacterial fusion. The bacterial conjugation and it will start to transfer some D. N. A. Into the other cell in forms of recombination. Now the origin is the area where the first gene transfers of the first recombination areas start transferring to the other cell. Now at any point you can stop conjugation or humans can um and they when they stop it it's called interrupted mating. And literally what they do is they take bacteria who are undergoing conjugation and they put them in a blender like really like gentle blender. And that that stops all conjugation right? Because it cuts that conjugation bridge that pillai apart. And so now it can't finish what it's doing but it's already started it but it can't finish. So what happens is you actually get some of the genes that were really close to this HFR which is where it started. Um Well have already recombined before you interrupted it. So let's say you allowed conjugation for five minutes and interrupted at five minutes. Well the genes that are really close to the HFR will have already recombined in that five minute time and the genes that are far away won't have had time to recombine in that period. So you can actually use minutes from like you're interrupted mating from time of conjugation. Starting to determine how close the jeans are too that HFR. So this is what this looks like in the similar path. So here you have the HFR it has the pill, it can conjugate you can see that um it's getting transferred. It's it's undergoing it's allowing recombination between these two bacteria. So here's the origin which is where that started and it always starts with that HFR And then the genes that are really close to that HFR if you interrupt it very quick soon after conjugation will have stopped right then you can map how close those genes are to the HFR based on minutes past interruption. So with that, let's not move on.

Okay so bacteria actually contain other plasmas in addition to the F. Factor. So like I said before there are 270 different types of plasmas. Um and the main one that we talked about is the f. Factor obviously because of its importance and conjure. But another really important one I talk about is the our plasma and this is the plasma that allows bacteria to confer antibiotic resistance. So we hear about these superbugs and like you know take all of your antibiotics because you don't want superbugs and they're killing people all over the place and being a little dramatic here but you hear about them in the news and that's how they present it. Um And so that our plasma is what allows bacteria to do this. So these these plasma. So if one bacteria has a our plasma that's resistant to penicillin and there are other bacteria around it can actually be transferred between bacterial species. It doesn't have to be the same species. It can be any bacteria that just sort of around it and it can say hey I can grow without you know in the presence of penicillin. And all the bacteria are like oh my goodness give me that plasma. And so they do. And so all these different bacterial species now become resistant to penicillin which is obviously a horrible thing. Now the are plasmas are really effective and they're different from the F. Factor because they contain an extra thing on it that's super important. These things are called transpose on. Now you may have heard of transposes before if you have it, it's totally okay we'll talk about them. But essentially what a transpose is and just brief form is that it's called jumping gene and this gene can sort of cut itself out of wherever it is and and sort of jump to a different part of the organism or in this case for the our plasma actually different organisms completely. So the our plasma contains a transpose on. And that transposing will allow it to cut out of the bacteria is in and transfer into other bacteria and so it can assist in this DNA transfer. And it's part of the reason why it allows it to be able to jump between all of these different bacterial species. So this is a really important plasma that our plasma does antibiotic resistance. So with that let's move on.