Hi everyone, and welcome to Biology Professor. Today, I want to talk about
genetic recombination in bacteria. Bacterial cells are pretty cool because
they have the ability to take up foreign DNA and actually incorporate it into
their own genetic profile in order to make the protein that foreign DNA
encoded for. This can give bacterial cells extra functionality, for example, they
might gain new DNA that codes for toxins, that codes for virulence
factors, that codes for antibiotic resistance, and the bacterial cell can
actually gain new functionality through this way. There are three different
mechanisms by which bacteria can obtain foreign DNA. These are transformation,
conjugation, and transduction. I have videos on all three of these mechanisms,
but today, let's talk about first one: transformation. Transformation is when a
bacterial cell takes up foreign DNA from its environment by bringing that DNA
from its extracellular environment across its plasma membrane. The ability
of the cell to take up DNA across its plasma membrane in this way is called
competence.
Many types of bacteria are naturally competent and they can do this
process with ease. Examples of such bacteria include species of Bacillus,
species of Staphylococcus, and species of Streptococcus, and of course there are
well-known human pathogens within each of these types of bacteria. So now let's
look at this mechanism in a little more detail. Here we have our recipient
bacterial cell. This here is its chromosomal DNA. So this
is the DNA that it has had since it was produced by replication of previous
bacterial cells. But there might be foreign DNA in this cell's environment. I'm
going to draw this foreign DNA in red. This is DNA that is just going to be
floating through the cell's environment. It might, for example, be from a previous
bacterial cell that died and lysed, and pieces of its of this donor cell's DNA
are now just floating around the environment. The recipient bacterial cell
can actually take this DNA across its plasma membrane so that now this DNA is
inside the cell, then through the process of recombination,
the bacterial cell has its chromosomal DNA that has recombined with this
foreign DNA so the foreign DNA has now been integrated into the chromosome.
There might be some additional foreign DNA that was not integrated and it's
just going to be broken down. Also, the bacterial DNA that was replaced by
this foreign DNA is also going to be broken down and now we have this
genetically transformed bacterial cell. This new DNA that's taken up can give it
different functions, for example there are species of E. coli that actually
produce Shiga toxin. This is a toxin that they obtained from the bacteria
Shigella, so Shigella produces shiga toxin, some E. coli cells can
produce it too because they're able to go through this genetic recombination
process. This DNA could also encode for virulence factors, for example one virulence
factor might be a capsule. If the bacteria can produce a capsule
covering its outer cell wall, this may enable it to hide from a host immune
system, and so this is why the process of transformation is very important to
bacterial cells in that it can enable them to survive in different
environments they might not have been able to otherwise.