Bacterial Conjugation: A process of genetic transfer between bacterial cells requiring direct cell-to-cell contact.
Species Capability: While not all bacterial species can conjugate, many do. Conjugation can occur within the same species or between different species.
Key Components
F Factor (Fertility Factor):
A small DNA circle or plasmid essential for conjugation.
Bacteria containing the F factor are termed F+ (F plus).
Bacteria lacking the F factor are termed F- (F minus).
Process of Conjugation
Pilus Formation:
An F+ cell or donor produces a structure called the pilus to connect with a recipient cell (F-).
Initiation of Transfer:
The F factor is cut at the origin of transfer by the relaxosome, a protein assembly.
The relaxosome associates with the strand to be transferred, known as the T-DNA strand.
Relaxosome Function:
Accessory proteins of the relaxosome are released, but a portion, called the relaxase, remains attached to the T-DNA.
Transfer Mediation:
The T-DNA-relaxase complex is recognized by a coupling factor.
The complex is transferred to the exporter, a part of the F+ cell that is contiguous with the pilus.
DNA Transfer:
The exporter pumps the T-DNA-relaxase complex into the recipient cell.
Once transferred, relaxase joins the ends to form a circular DNA in the recipient cell.
Replication:
As the T-DNA is transferred, it is replicated to become double-stranded in the recipient cell.
In the donor cell, F factor DNA is also replicated and becomes double-stranded as the T-DNA is transferred.
Completion:
At the end of the process, both cells have a complete double-stranded copy of the F factor.
The connection through the pilus is released, resulting in both cells being F+ and capable of further conjugation.