A Broad Brush, Global Overview of Bacterial Sexuality

Abstract

Bacterial sexuality is confusing, even for experts! I used to be such an expert on one mechanism of sexuality, conjugation, but that was over 30 years ago. At that time, extra-chromosomal elements, so-called plasmids, were known to encode multiple proteins that together enabled cell-to-cell contacts, which were then used to transfer single-stranded DNA from donor to recipient, thus providing the plasmid with a new host. Transfer of the plasmid resulted in concomitant transfer of any genes that it happened to include, such as genes encoding resistance to antibiotics or virulence factors. On unusual and rare occasions, the plasmid integrated into the chromosome, resulting in the conjugative transfer of chromosomal DNA. What was particularly confusing was the plethora of plasmids that encoded genes for conjugation, each apparently different from the other, and the corresponding large variety of differences between mechanisms of conjugation associated with different plasmids. Some plasmids didn't even encode genes for conjugation, but simply hitch-hiked with the help of conjugation proteins expressed by other plasmids, a phenomenon called mobilization.