Bacterial Sex

∞ generated and posted on 2016.12.17 ∞

Exchange of genetic material among prokaryotes.

Sex is the exchange of genetic material between different organisms, resulting in recombinant offspring. Bacteria are not obligately sexual for their replication and consequently do not engage in sex at least once per successful reproductive episode as do obligately sexual organisms such as ourselves.

Sex in bacteria usually involves the acquisition of far less than the total genome of one parent by a second parent, the donor cell and the recipient cell, respectively. The latter then integrates the first parent's DNA into its genome in some manner (usually but not always involving some form of molecular recombination). The different forms of bacterial sex traditionally have been distinguished in terms of the means by which the first bacterium's DNA ends up in the cytoplasm of the recipient cell, what are described as transformation, conjugation, and transduction. See also horizontal gene transfer.

Figure legend: The major routes of exchange of genetic material among bacteria are termed transformation, transduction, and conjugation. In each case substantially subchromosomal quantities of DNA are transferred, here termed 'snippet'. In both transformation and transduction the bacterium often does not survive the process of donation of genetic material. While transformation is a bacterium-mediated mechanism (that is, chromosomally encoded), transduction is mediated by bacteriophages, which are somewhat autonomous from the bacterial genetic program. Conjugation instead is mediated by plasmids, which also are somewhat autonomous from the chromosomal bacterial genes. Following snippet acquisition – in the case of transformation and transduction – snippet survival within the recipient cell is dependent on molecular recombination of that snippet into the bacterial chromosome.

Though not something that is at the forefront of most of our thinking, bacterial sex nonetheless turns out to be hugely important to bacterial evolution and even medical microbiology. Most familiar is bacterial acquisition of antibiotic resistance plasmids which typically occurs via conjugation.

Equally important, to medical microbiology, is the potential for bacteria to acquire pathogenicity islands from other bacteria, greatly contributing to the virulence of various bacterial strains, and which they can acquire via transduction. In another form of transduction, bacteria can acquire numerous virulence factor and exotoxin genes. Lastly, in the absence of sex, bacterial populations over long periods can experience a form of genetic decay commonly described as Muller's ratchet.