#bacterial conjugation

Microbial Physiology

Antibiotic resistance genes are commonly transferred between bacteria via:

Vertical inheritance through binary fission faithfully copies the single circular chromosomal DNA with high fidelity via DNA polymerase III holoenzyme but fails to explain extraordinarily rapid global dissemination of antibiotic resistance observed within decades of antibiotic introduction. Horizontal gene transfer provides direct mechanism for movement of accessory genes between genetically unrelated cells, even across genus barriers. Conjugation involves direct cell-to-cell contact via retractile sex pilus encoded by tra operon and transfer of conjugative plasmids and integrative conjugative

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: Horizontal Gene Transfer and Resistance Spread.

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Microbial genetics

F′ plasmid formation occurs due to

F' plasmid formation results from imprecise excision of integrated F factor in Hfr chromosome. F integration involves homologous recombination between plasmid and chromosome IS sequences. When excising, recombination occurs between homologous sites but at incorrect boundaries, looping out plasmid that carries adjacent chromosomal segment flanking oriT. Resulting F' retains tra genes plus chromosomal genes like lac, making larger hybrid plasmid. Upon transfer, recipient becomes partial diploid for those genes. Correct excision regenerates normal F+ and leaves chromosome intact without extra bac

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 6: F Prime Formation Mechanism

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Microbial genetics

Hfr strain differs from F+ strain because

F+ strains carry autonomous F plasmid extrachromosomally, expressing pili and transferring only F DNA in crosses, donor ability but chromosomal genes transfer at very low frequency. Hfr strains arise when F integrates into bacterial chromosome via homologous recombination at IS elements, creating single linkage between F origin oriT and chromosome. Upon conjugation, transfer initiates at integrated oriT and proceeds linearly into chromosomal DNA, transferring chromosomal markers with high efficiency in order determined by integration site and orientation, converting recipients to recombinants

Ref: Wollman & Jacob 1956, Comptes Rendus; Griffiths et al., Chapter 6: Hfr vs F+ Biology

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Microbial genetics

F plasmid is involved in

F plasmid, or fertility factor, is 100 kb conjugative plasmid carrying tra operon encoding sex pili, type IV secretion system, and regulation of cell contact. Cells harboring F express F pili, act as donors F+ and initiate conjugation by transferring single-stranded copy of plasmid to F- recipient via pilus. F also integrates rarely to form Hfr. Its role is horizontal transmission of itself and mobilization of other DNAs, spreading genes like antibiotic resistance. Classic Lederberg-Tatum experiments used F to demonstrate bacterial recombination, revolutionizing prokaryotic genetics analysis.

Ref: NCBI Bookshelf, F Factor and Conjugation; Griffiths et al., Chapter 6: Bacterial Mating

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