a form of horizontal gene transfer in which bacterial cells transfer DNA to one another through direct cell-to-cell contact. The donor has a conjugation plasmid (one of those circular pieces of DNA, but this one’s special – it has instructions for making a conjugation pilus (sex pilus or F pilus)). The donor uses those instructions to make a sort of “hand” that stretches out from the cell, grabs onto another cell, then pulls it close and a “bridge” forms between them that DNA can travel through. It doesn’t want to send its “only copy” through, but thankfully, the conjugative plasmid is double stranded, so the donor sends one strand through, then both cells copy the strand they have to recreate the double-stranded form. Now the recipient bacteria has the conjugation plasmid and can serve as a donor. This is a common way in which cells can gain bacterial resistance because the conjugation plasmids also often have antibiotic resistance genes – we call such plasmids R-plasmids.
