Gene Transfer In Bacteria I: Conjugation Hfr Conjugation Sexduction
Gene Transfer In Bacteria I: Conjugation Hfr Conjugation Sexduction
Bacteria exchange genetic material through three different parasexual processes:
- Conjugation
- Transformation
- Transduction
Conjugation
- Conjugation in bacteria was discovered in 1946 by J Lederberg and E.L. Tatum and confirmed by Bernard Davis in 1950 by the famous U-tube experiment which showed that conjugation required physical contact.
- Conjugation is a process which involves physical matting between sexually differentiated strains of bacteria for the unidirectional transfer of genetic material. Or
- Conjugation is a one- way transfer of genetic material in bacteria from a donor (male cell) to recipient (female cell) by formation of close physical contact (Pilus).
- It is parasexual reproduction (parasexual because it does not involve formation of true gametes or gamete fusion) in bacteria.
Properties
- For conjugation close physical contact between bacterial cells are needed.
- Gene transfer is unidirectional from donor (F+ cell) to recipient (F–cell).
- Donor F+ cells carry a plasmid called the fertility factor or F factor or F plasmid a circular extrachromosomal molecule containing about 94,000 np.
- Genes on the F factor are responsible for facilitating cell-cell contact and F factor transfer from donor to recipient cell.
- Many F factor genes direct the synthesis of sex pili (singular pilus), a filamentous appendages on the bacterial surface that attach F+ cells to F– cells.
- The F factor and the main bacterial chromosome have insertion sequences (ISs) that enable the F factor to insert into the chromosome by homologous recombination.
- Insertion sequences are short, transposable DNA sequences that contain a gene encoding an enzyme called transposase which the movement of the insertion sequence around the genome.
