The process of Bacterial conjugation

The Conjugation Process:

An F-plasmid gene confers the ability to produce long, hair-like appendages, known as sex pili (F-pili). These appendages establish contact with F-cells which are without sex-pili. The sex pilus is then retracted within the P cell, bringing the F cell to come in contact with the F cell. The enzymes coded by the F-plasmid are then used to build a mating bridge which establishes a direct contact between the two conjugating cells.

Next, replication of the F-plasmid begins by producing a nick in a single strand of the double- stranded plasmid DNA at a specific site, called the transfer origin (OriT). A protein (probably the nicking enzyme) itself remains bound to the 5′-end of the nicked DNA strand and effects transfer of the nicked strand into the recipient (F) cell through the mating bridge.

The replication of the plasmid DNA occurs by the rolling circle model in which the strand which is being transferred is regenerated by new DNA synthesis in the 5′ —> 3′ direction. Simultaneously, a DNA strand complimentary to the transferred strand is synthesized in the F cell. After completion of the transfer, the two regenerated strands are sealed by ligaso. The two cells separate and each of them now has a copy of the complete F-plasmid. Thus, both the donor and the recipient become F+.

The sequences of events in the conjugation process are shown in Fig. 1.: