INVOLVEMENT OF OUTER-MEMBRANE PROTEIN TOLC, A POSSIBLE MEMBER OF THE MAR-SOX REGULON, IN MAINTENANCE AND IMPROVEMENT OF ORGANIC-SOLVENT TOLERANCE OF ESCHERICHIA-COLI K-12

Escherichia coli mutants with improved organic solvent tolerance level s showed high levels of outer membrane protein TolC and inner membrane protein AcrA. The TolC level was regulated positively by MarA Rob, or SoxS. A possible mar-rob-sox box sequence was found upstream of the t olC gene, These findings suggest that tolC is a member of the mar-sox regulon responsive to stress conditions. When a defective tolC gene wa s transferred to n-hexane- or cyclohexane-tolerant strains by P1 trans duction, the organic solvent tolerance level was lowered dramatically to the decane-tolerant and nonane-sensitive level. The tolerance level was restored by transformation of the transductants with a wild-type tolC gene. Therefore, it is evident that TolC is essential for E. coli to maintain organic solvent tolerance.