Molecular basis of conjugation-mediated DNA transfer by gram-negative bacteria

Bacterial conjugation is the unidirectional transfer of DNA (often plasmids, but also other mobile genetic elements, or even entire genomes), from a donor cell to a recipient cell. In Gram-negative bacteria, it requires the formation of three complexes in the donor cell: i-a large, double-membrane-embedded transport machinery called the Type IV Secretion System (T4SS), ii-a long extracellular tube, the conjugative pilus, and iii-a DNA-processing machinery termed the relaxosome. While knowledge has expanded regarding molecular events in the donor cell, very little is known about the machinery involved in DNA transfer into the recipient cell. Here, focusing on systems principally involved in DNA transfer, we provide an update on progress made on various mechanistic aspects of conjugation.