Introductory Microbiology

III. Conjugation

Conjugation

• Bacterial conjugation (mating) is a process of genetic recombination that involves cell to cell contact. The gene for conjugation (ability to mate) is a plasmid borne character. The gene involves the conjugation is designated as F factor (fertility factor) which located in the plasmid (referred as F plasmid). The cell which has the F plasmid is donor (male) designated as F+ cells and the cell does not have the F plasmid is the recipient (female) designated as F- cells. The DNA will be transferred from donor to recipient through physical contact. So another requirement for cell to cell contact is sex pilus through which the donor DNA will be transferred to recipient cell.
• The diagrammatic representation shows how the conjugation takesplace. The sex pili makes a connection between donor and recipient. A nick (split) in the complementary strand of F plasmid takes place. The single strand plasmid transferred to F- cell and become double stranded. The F+ cell also synthesized its cDNA and become double strand. After conjugation both the cells become F+ cells.

Hfr cells
Some times, F plasmid transferred from F+ cell to F- cell get integrated into recipient cell chromosomal DNA. Such conjugates possess the F factor in the chromosomal DNA instead of plasmids. They are referred asHFRcells (high frequency recombination). They have very high frequency of conjugations.