Entry into and release of solvents by Escherichia coli in an organic-aqueous two-liquid-phase system and substrate specificity of the AcrAB-TolC solvent-extruding pump

Growth of Escherichia coli is inhibited upon exposure to a large volume of a harmful solvent, and there is an inverse correlation between the degree of inhibition and the log P-OW of the solvent, where P-OW is the partition coefficient measured for the partition equilibrium established between the n-octanol and water phases. The AcrAB-TolC efflux pump system is involved in maintaining intrinsic solvent resistance. We inspected the solvent resistance of Delta acrAB and/or Delta tolC mutants in the presence of a large volume of solvent. Both mutants were hypersensitive to weakly harmful solvents, such as nonane (log P-OW = 5.5), The Delta tolC mutant was more sensitive to nonane than the Delta acrAB mutant. The solvent entered the E, coli cells rapidly. Entry of solvents with a log P-OW higher than 4.4 was retarded in the parent cells, and the intracellular levels of these solvents were maintained at low levels. The Delta tolC mutant accumulated n-nonane or decane (log P-OW = 6.0) more abundantly than the parent or the Delta acrAB mutant. The AcrAB-TolC complex likely extrudes solvents with a log P-OW in the range of 3.4 to 6.0 through a first-order reaction. The most favorable substrates for the efflux system were considered to be octane, heptane, and n-hexane.