Derepression of F factor function in Salmonella typhimurium

Area of Science:

• Microbiology
• Bacteriology
• Genetics

Background:

• The F factor from Escherichia coli K-12 normally replicates in Salmonella typhimurium LT2 but is repressed.
• This repression results in a fertility inhibition (Fin+) phenotype, characterized by low phage propagation and conjugation efficiency.

Purpose of the Study:

• To investigate the mechanism of F factor repression in Salmonella typhimurium LT2.
• To identify methods to circumvent this repression and restore F factor function.

Main Methods:

• Utilized mutant F plasmids (finP, traO), S. typhimurium strains cured of pSLT, and a compatible plasmid (pKZl) to induce pSLT expulsion.
• Employing spontaneous F-Fin- mutants and Hfr strains of S. typhimurium.

Main Results:

• Repression of the F factor in S. typhimurium LT2 is mediated by the resident pSLT plasmid through the FinOP system.
• Circumventing pSLT-mediated repression restored F factor function, leading to visible lysis with male-specific phages, increased conjugation efficiency, and high phage titers.
• Derepressed F-mediated conjugation in S. typhimurium LT2, using rough recipient strains, achieved efficiency comparable to E. coli K-12.

Conclusions:

• The pSLT plasmid is the sole determinant of F factor repression in S. typhimurium LT2 via the FinOP system.
• Efficient F-mediated conjugation can be achieved in S. typhimurium LT2 by overcoming pSLT-mediated fertility inhibition.