Improving the organic solvent tolerance of Escherichia coli with vanillin, and the involvement of an AcrAB-TolC efflux pump in vanillin tolerance

Abstract

Vanillin is used as a flavor ingredient in a diverse range of food categories and is known to inhibit microbial fermentation. In this study, we found that vanillin improved the hydrophobic organic solvent tolerance of Escherichia coli and showed that the AcrAB-TolC efflux pump is implicated in that tolerance. The expression level of the pump was enhanced by the addition of vanillin. AcrAB-TolC efflux pump expression is known to be regulated by transcription activators such as MarA, SoxS, and Rob. Among these three transcription factors, marA transcription was significantly elevated by the addition of vanillin. We found that the AcrAB-TolC efflux pump is involved also in vanillin tolerance. The ΔacrB mutant was more sensitive to vanillin than the parent strain. A complementation test revealed that the introduction of the acrB gene recovered the vanillin tolerance of the ΔacrB mutant.