title: AcrAB multidrug efflux pump regulation in Salmonella enterica serovar Typhimurium by RamA in response to environmental signals.
abstract: Salmonella enterica serovar Typhimurium has at least nine multidrug efflux pumps. Among these pumps, AcrAB is effective in generating drug resistance and has wide substrate specificity. Here we report that indole, bile, and an Escherichia coli conditioned medium induced the AcrAB pump in Salmonella through a specific regulator, RamA. The RamA-binding sites were located in the upstream regions of acrAB and tolC. RamA was required for indole induction of acrAB. Other regulators of acrAB such as MarA, SoxS, Rob, SdiA, and AcrR did not contribute to acrAB induction by indole in Salmonella. Indole activated ramA transcription, and overproduction of RamA caused increased acrAB expression. In contrast, induction of ramA was not required for induction of acrAB by bile. Cholic acid binds to RamA, and we suggest that bile acts by altering pre-existing RamA. This points to two different AcrAB regulatory modes through RamA. Our results suggest that RamA controls the Salmonella AcrAB-TolC multidrug efflux system through dual regulatory modes in response to environmental signals.
authors.affiliation: Department of Cell Membrane Biology, Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Nikaido
authors.forename: Akihito
authors.initials: A
authors.lastname: Yamaguchi
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Nishino
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics; D019826:Cholic Acid / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects* / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects* / Q000502:physiology; D007211:Indoles / Q000378:metabolism / Q000494:pharmacology; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000096:biosynthesis* / Q000235:genetics; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D015534:Trans-Activators / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D019826:Cholic Acid; D007211:Indoles; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D015534:Trans-Activators; C493251:AcrAB-TolC protein, Salmonella enterica; C531999:RamA protein, Salmonella typhimurium; C030374:indole