IMPROVEMENT OF ORGANIC-SOLVENT TOLERANCE LEVEL OF ESCHERICHIA-COLI BYOVEREXPRESSION OF STRESS-RESPONSIVE GENES

Water-immiscible organic solvents can be toxic to microorganisms. The tolerance levels differ among strains of Escherichia coli, suggesting that the organic solvent tolerance level is strain specific and determ ined genetically. We constructed several mutants from E. coli, of whic h the organic solvent tolerance levels were improved. The mutants were defective in the marR gene encoding a repressor protein for the mar o peron that is responsible for environmental stress factors. High expre ssion of stress-responsive genes, soxS, marA, and robA, elevated organ ic solvent tolerance levels of several strains of E. coli. These genes code for DNA-binding proteins that are transcriptional activators bel onging to the AraC subfamily with the helix-turn-helix motif. It was s hown that expression of the AcrAB-TolC system, a major efflux pump in E. coli, was positively regulated by the proteins. This system was hig hly expressed in the organic solvent-tolerant mutants. Strains defecti ve in one of the genes, acrA, acrB, or tolC, were remarkably sensitive to organic solvents.