PacB, a plasmid-encoded property which confers to E. coli K12 resistance to channel-forming colicins

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Colicins are bacteriocins produced by bacteria.
• Colicins exhibit diverse mechanisms of action, including pore formation and DNA/RNA degradation.
• Plasmids are extrachromosomal DNA molecules that can confer various traits to host bacteria, such as antibiotic resistance.

Purpose of the Study:

• To investigate the role of specific plasmid incompatibility groups in conferring resistance to colicin B in E. coli.
• To determine the spectrum of colicins against which the plasmid-encoded property (PacB) provides protection.
• To assess the conservation of this protective property among different plasmid types.

Main Methods:

• Bacterial conjugation experiments to transfer plasmids into E. coli.
• Bactericidal assays to measure bacterial survival upon exposure to various colicins.
• Plasmid incompatibility grouping and characterization.

Main Results:

• Plasmids from incompatibility groups HI2, HI3, and HII conferred resistance to colicin B in E. coli.
• The plasmid-encoded property, designated PacB, was effective against a range of channel-forming colicins (A, B, E1, Ia, Ib, K, N).
• PacB+ E. coli remained susceptible to colicins with non-channel-forming mechanisms of action.
• The PacB property was found to be highly conserved among HI2 plasmids.

Conclusions:

• Specific plasmids, particularly HI2, HI3, and HII incompatibility groups, confer significant resistance to E. coli against colicin B.
• The identified plasmid-encoded property, PacB, broadens bacterial resistance to multiple channel-forming colicins, not just colicin B.
• PacB confers a specific type of colicin resistance, leaving bacteria susceptible to colicins with alternative modes of action.
• The high conservation of PacB among HI2 plasmids suggests a significant evolutionary role for this protective mechanism.