Gene Transfer In Bacteria-I: Conjugation​   (F+ x F- conjugation, Hfr Conjugation,  F’ Conjugation or Sexduction)​

Gene Transfer In Bacteria-I: Conjugation​ (F+ x F- conjugation, Hfr Conjugation, F’ Conjugation or Sexduction)​

February 18, 2022

Gene Transfer In Bacteria-1

Conjugation (F+ x F– conjugation, Hfr Conjugation,  F’ Conjugation or 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 (Fcell).
  • 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 F­cells 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.

 

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