Escherichia coli mar and acrAB mutants display no tolerance to simple alcohols

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• The inducible Mar (multiple antibiotic resistance) phenotype in Escherichia coli confers tolerance to hydrophobic antibiotics and solvents via the AcrAB/TolC efflux system.
• Understanding E. coli's response to various solvents is crucial for industrial and research applications.

Purpose of the Study:

• To investigate the influence of water-miscible alcohols (ethanol, 1-propanol) on E. coli strains with different Mar and AcrAB/TolC efflux system statuses.
• To determine if the Mar phenotype or the AcrAB/TolC efflux system confers tolerance to polar organic solvents.

Main Methods:

• Comparative analysis of E. coli K-12 strains: wild-type, constitutive Mar mutant, mar deletion mutant, and strains with additional acrAB deletions.
• Exposure of bacterial cultures to ethanol and 1-propanol at exponential phase.
• Assessment of bacterial killing rates in the presence and absence of sodium salicylate.

Main Results:

• All tested E. coli strains exhibited comparable susceptibility to killing by ethanol and 1-propanol, indicating no protection by the Mar phenotype.
• The AcrAB/TolC efflux system did not contribute to increased tolerance to these alcohols.
• Sodium salicylate, known to induce the mar operon, did not enhance alcohol tolerance and instead increased solvent toxicity.

Conclusions:

• E. coli's resilience to water-miscible alcohols is independent of the AcrAB/TolC efflux system, unlike its response to hydrophobic solvents.
• This suggests a molecular size or functionality limit for substrates handled by the AcrAB/TolC efflux system.
• Findings have implications for using microbial systems in environments with high concentrations of water-miscible organic solvents.