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, you know, several billion years now, we can certainly see lots
of evidence of it happening. So, you know, 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 and other organisms in there as a result of
lateral gene transfer. However, bacteria do lateral gene transfer like no other organisms,
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 plasmid DNA is shared between bacteria via sex pilus. And then there's transduction.
And this one, 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. The first one I want to mention is transformation. And we've talked about
transformation before because when we talked about the discovery of DNA, we talked about
Avery, McCloid 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-killed the S strain, the strain with a capsule and you added that to the living
R strain, what has happened was that the R strain 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 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 a little video, I don't believe
it has any words. So let's watch it just live here. Oops, 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. Alright, so really short, not worth making 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 plasmid DNA will 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, 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 and 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 Staphylococcus, but a lot of bacteria are not. And because of this, when we use
transformation, in molecular biology, we have 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 plus cell - this 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 pilus and then the plasmid itself will get copied, and it will move through
the sex pilus into this cell and when they're done they will both be F plus they will both
have copies of this pilus (plasmid). 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 pili which allow the exchange
of genetic material All right, well, you get the idea and some
great music to go along with it. But now our two organisms now both have this plasmid.
And the plasmid is depicted is really large and 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 that the pilus is formed, it forms
a bridge between the two organisms and then you have 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 pilus with the F plus donor cell, and the F minus recipient cell. Alright, 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