Gene Transfer Between Bacteria

Genetic diversity in bacteria comes from mutations or genetic transfer.

There are three types of genetic transfer: conjugation, transformation, and transduction.

Conjugation

Conjugation is when a direct physical interaction transfers genetic material from a donor cell to a recipient cell.

Only about 5% of E. coli strains found in nature cam act as a donor strain.

Donor strains contain a fertility factor (F factor) that can be transferred to recipient strains. Some donor strains are Hfr, for high frequency of recombination.

F factors carry several genes that are required for conjugation and may also carry genes that confer growth advantage. F+ has an F factor and F- does not. Sex pili are made by F+ cells that bind specifically to F- cells. Once contact is made, the pili shorten to draw the cells closer together. One strand of F factor is transferred while the other strand stays in the donor. They both replicate so that the donor and recipient have a complete double stranded F factor.

Transformation

Transformation doesn’t require direct contact between bacterial cells. Instead, living bacterial cells will import a strand of DNA that another bacterial cell released into the environment when it died.

Only competent cells with competence factor are capable of transformation. Competence factors facilitate binding of DNA fragments to the bacterial cell surface, the uptake of DNA into the cytoplasm, and the incorporation of imported DNA into the bacterial chromosome.

Transduction

Viruses that infect bacteria can transfer bacterial genes from one bacterial cell to another.

Transduction usually occurs due to an error in a phage lytic cycle, and involved new assembled phages incorporating a piece of the host DNA instead.