Overproduction of AcrR increases organic solvent tolerance mediated by modulation of SoxS regulon in Escherichia coli.

Acriflavine resistance regulator (AcrR), a local transcription factor, regulates the expression of the acrRAB genes associated with the AcrAB-TolC multidrug efflux pump. Screening of organic solvent tolerance (OST) with the overexpression of 13 genes in Escherichia coli revealed that the overexpression of acrR improved OST. Overexpression of AcrR in a background strain of wild-type E. coli and in the OST strain LMB015 (ΔfadR ΔmarR; acrR (+) and ΔfadR ΔmarR acrR (+) strain, respectively) significantly increased cell growth in the presence of n-hexane/cyclohexane, which attenuated the membrane reduction capacity of the wild-type strain below 50 % of the control level. This was recovered to control levels in the acrR (+) strain. Quantitative real-time PCR analysis of RNA from the wild-type, ΔacrR, and acrR (+) strains showed that AcrR represses the transcription of marRAB and soxRS, and its own gene cluster, acrRAB. Electrophoretic mobility shift assay demonstrated that AcrR binds directly to the promoter region of acrRAB, marAB, and soxRS, indicating that AcrR acts on global regulators to affect mar-sox-rob regulon. In the acrR (+) strain, soxS expression was significantly upregulated compared with the wild-type. The OST of the acrR (+) strain was completely lost in the ΔsoxS acrR (+) strain, indicating that SoxS mediated OST improvement in the acrR (+) strain. The observation that all genes associated with marRAB and soxRS are upregulated in the ΔacrR strain, and that there is only moderate induction of soxS (and marB) in the acrR (+) strain, provides insight into how acrR overexpression confers bacterial OST and the mar-sox-rob regulon control network.