ColB2-K77, a fertility-repressed F-like factor

Area of Science:

• Molecular Biology
• Bacteriology
• Genetics

Background:

• The colicinogenic B factor (ColB2) from Escherichia coli is an F-like conjugative plasmid.
• ColB2 exhibits repressed fertility, influencing its own transfer and affecting F-factor mediated processes.
• Understanding plasmid interactions and fertility regulation is crucial in bacterial genetics.

Purpose of the Study:

• To investigate the fertility regulation of the colicinogenic B factor (ColB2) in E. coli.
• To characterize the interaction between ColB2 and other conjugative elements like F and R factors.
• To identify and analyze mutants of ColB2 with altered fertility regulation.

Main Methods:

• Transfer of ColB2 to E. coli K12 F(-) strains.
• Analysis of plasmid transfer rates under low (LFC) and high (HFC) cell frequency conditions.
• Assessing F-specific phage adsorption and plaque formation.
• Investigating the effect of ColB2 on F factor fertility (chromosomal transfer and phage sensitivity).
• Isolation and characterization of fertility derepressed (Fdr) mutants of ColB2.
• Compatibility studies with R(f) and R(i) type drug resistance factors.

Main Results:

• ColB2 is an F-like sex factor with repressed fertility, evidenced by low transfer rates and suppressed F-specific phage adsorption in LFC cultures.
• ColB2 represses F factor fertility, indicated by reduced F-specific phage plaque formation and chromosomal transfer in co-infected strains.
• Fertility derepressed (Fdr) mutants of ColB2 exhibit high transfer frequency, F-specific phage sensitivity, and lack of repression on F factors.
• ColB2 is incompatible with R(f) factors but compatible with R(i) factors.
• The repressors for ColB2 and R(f) factors appear distinct, suggesting independent regulation of fertility.

Conclusions:

• ColB2 functions as a fertility-repressed conjugative plasmid, regulated by a cytoplasmic repressor.
• The Fdr mutation likely results from the inability to synthesize this repressor, leading to derepressed fertility.
• Distinct repressors for ColB2 and R(f) factors suggest independent control mechanisms for plasmid fertility.