As they said in that last video, the transfer of genes laterally between species other than bacteria is actually fairly uncommon. Because it's been happening for several billion years now, we can certainly see lots of evidence of it happening. So if a little piece of DNA is transferred, it gets copied and then shared from parent to child and parent to child.
So if we look at your genome, we see the ghosts of many viruses. other organisms in there as a result of lateral gene transfer. However, bacteria do lateral gene transfer like no other organism. They are experts at it and this is something that's done routinely between bacterial cells. There are three major types of lateral gene transfer in bacteria.
So in transformation we have just a naked DNA molecule is taken up by something called a competent bacteria and that That just means that a bacteria is either naturally able to take up foreign DNA or we've treated it with chemicals in the lab to make it competent. There's conjugation. So this is when plasma DNA is shared between bacteria via a sex pellus.
And then there's transduction. And this is when a bacteriophage basically carries DNA from one host to another host. And so we're going to talk about all three of these different types of lateral gene transfer in bacteria.
bacteria. The first one I want to mention is transformation. We've talked about transformation before because when we talked about the discovery of DNA, we talked about Avery, McLeod, and McCarty and how they took Streptococcus pneumoniae and when the bacteria had a capsule, it killed the mouse and when it didn't, the mouse survived.
But if you heat kill the S strain, the strain with a capsule and you added that to the living r strain what happened was that the r-frame was able to take up dna from the s-strain and develop a capsule and then it would be able to kill the bacteria so this is a an early example of our use of transformation to actually study in this case what try to understand better what the genetic material was this is the little video i don't believe it has any words so let's watch it just live here Oops, that didn't work very well. There we go. Some bacteria possess surface proteins that can transport DNA from closely related cells, allowing a process called transformation.
When a bacterial cell dies, it can break open and release DNA, which can be taken in by closely related species and incorporated into their genomes. All right, so really short, not worth making it a separate video. There was a few words to accompany that. I'll make sure this is fully captioned for you.
So that's transformation, pretty straightforward. Here's another picture just showing the kinds of transformations. So sometimes when a bacterial cell breaks apart when it dies, those little pieces can get into a nearby cell, and the cell can actually incorporate those pieces into its own genome. So you can see that in this particular case, the genome of the new bacteria, it has bits of the old bacteria actually completely integrated into it. This is called a stable transformation because this will continue to be copied along with the bacterial genome for the rest of the life of the cell, as many times as it's able to divide.
Another type of transformation is what we do in genetic engineering. We actually will take plasma DNA, we'll modify it so you can see that lots of different genes have been added to this recombinant plasmid. If we've done the PGLO lab in microbiology lab, then you got to do this with PGLO, it's a recombinant plasmid, and we can actually take E.
coli, we can treat it with calcium chloride typically to make it more susceptible to taking up foreign DNA. We can mix these together and some of the E. coli will take up some of this plasmid.
And then we can trick the E. coli into making the proteins that are on these genes, and that's how you get an E. coli to make, for example, human insulin, many, many other medically relevant molecules that we use now in treating people with a variety of different illnesses. One of the things that's pretty interesting, and I'll add a live link to this in the video, that we've started to realize that this Ability for many bacteria to take up foreign DNA is less passive. It's not that they're just kind of laying there and absorbing it as it happens to fall on them.
It looks like some of these bacteria really go out of their way to actually produce little... appendages to grab foreign DNA and take it up. So this is an example of how important this type of genetic variability is in evolution and in survival for different bacteria. I've mentioned competence and I want to review again what competence means.
In order for a bacterium to be competent, it means that the DNA must pass through the cell wall in the cell membrane and that's not going to happen easily. In fact, Some are. Some bacteria are naturally competent, like Neisseria and Streptococcus and Saphilococcus, but a lot of bacteria are not.
And because of this, when we use transformation in molecular biology, we usually treat the cells with calcium chloride, which changes, we think. Actually, it's not totally understood how it works, but we think what it does is it affects the charge on the surface of the bacteria, helping the foreign DNA stick better to the cell wall. and then take up the foreign DNA.
And you can also do something called electroporation, where you add DNA to the bacteria and then you give them a little electric shock. And that also allows the bacteria to take up the foreign DNA. Okay, another process that occurs is something called bacterial conjugation. And when we talked about the structure of bacterial cells, we talked a little bit about conjugation at that point.
And this is an F... F plus cells is actually a transmission electron microscopy image. This particular image has been false colored so you can kind of see what's happening. But this is, these are two cells and this one has the plasmid. It's called an F plus cell.
And this cell does not have the plasmid. It's an F minus cell. When you put these cells into a culture together, this will spontaneously, this cell will spontaneously make the sex pillus. And then the plasmid itself will get copied. and it will move through the sex pillus into this cell.
And when they're done, it will be both the F plus, they will both have copies of this of this pillus. So I'm going to play this little video for you. Again, it's very short.
I'm just going to go ahead and play it in this video, embedded in this video. Plasmids carry genes that code for antibiotic resistance during conjugation. Plasmids can be rapidly exchanged between bacteria through pilar, which allow the exchange of genetic material. Let's get the best love baby.
Let's get sugar. Let's get the heart. We're almost at the peak. All right, well, you get the idea of some great music to go along with it, but now our two organisms now both have this plasmid.
And the plasmid is depicted as really large in the chromosomes over here, but this is really tiny compared to the chromosomes, so it's just bigger so that you can see it. That's bacterial conjugation. I've got one more diagram here for you to look at.
So again, the donor cell would be the F plus cell. It's got the plasmid. The pillus is formed. It forms a bridge between the two organisms. And then you have the...
the plasmid gets copied. It gets copied by a mechanism called rolling circle replication. And so what happens is it basically makes this little linear piece, which goes through the conjugation bridge, and then it's going to roll up and then ultimately make another copy. So it's double stranded. And now you have two F plus cells.
Here's another great transmission electron microscope picture of the sex pillus with the F plus donor cell and the F minus recipient cell. All right, I'm going to leave transduction for a separate video. It's a little bit more complicated, and we'll be talking about that next.