Fig. 1.

Conjugation. Conjugation systems (shown is the shot-and-pump model of conjugative DNA transfer) represent a large subfamily of the T4SSs and are used by bacteria in the process of the conjugative transfer of DNA from donor to recipient cells (A) by cell-to-cell contact usually mediated by the retraction of the pilus-like structures (B). C. ssDNA of the mobile genetic element is transferred from the donor to recipient bacteria with the help of the relaxase. D. Complementary DNA strands are synthesized in both cells and the former recipient bacterium becomes a new potential donor of the mobile DNA.