Yesterday I gave another talk, this one to the Biodiversity Centre in-house series. It was an evolution-focused version using my standard "Do bacteria have sex?" framework. This morning I realized that there's a point I should be making every time I use this framework.
Rather than describe the whole talk I've posted the slides to Slideshare (you can see them here). But you won't need to look at them to understand the point of this post. Early in these talks I always explain that, in bacteria, transfer of chromosomal genes between close relatives can occur by any of three 'parasexual' processes - conjugation, transduction and transformation. Incorporation of transferred alleles into the chromosome requires homologous recombination, mediated by an assortment of enzymes in the recipient cell. Then I describe the evidence that conjugation and transduction occur as unselected side effects of genes on parasitic genetic elements (plasmids and phages respectively) - the selected functions of these genes are infectious transfer of the parasites. And the evidence that all the enzymes that contribute to recombination have been selected for functions in DNA replication and repair, with no evidence of selection for the recombination effects.
At this point I have always next explained that transformation is thus the only bacterial process that still could have evolved for a sexual function (to promote recombination of chromosomal genes). But today I realized that I should first point out that this means that E. coli doesn't have sex, because E. coli is one of the many bacteria that don't have natural transformation.
The Green Sulphur Bacteria
5 hours ago in Catalogue of Organisms