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AcrAB multidrug efflux pump regulation in Salmonella enterica serovar Typhimurium by RamA in response to environmental signals.

Nikaido E, Yamaguchi A, Nishino K - J. Biol. Chem. (2008)

Bottom Line: Among these pumps, AcrAB is effective in generating drug resistance and has wide substrate specificity.Other regulators of acrAB such as MarA, SoxS, Rob, SdiA, and AcrR did not contribute to acrAB induction by indole in Salmonella.Our results suggest that RamA controls the Salmonella AcrAB-TolC multidrug efflux system through dual regulatory modes in response to environmental signals.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Membrane Biology, Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan.

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.

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Requirement of RamA for induction of acrAB by bile. β-Galactosidase levels were assayed in WT (NKS505) or ΔramA (NES58) strains carrying the acrAB-lac transcriptional fusion. Cells were grown in LB medium (control) or LB medium supplemented with 0.25 mm cholic acid, 0.25 mm deoxycholic acid, or 0.25 mm bile salts. The data correspond to mean values from three independent experiments. Bars correspond to the standard deviation. Student's t test; *, p < 0.01 versus WT.
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fig3: Requirement of RamA for induction of acrAB by bile. β-Galactosidase levels were assayed in WT (NKS505) or ΔramA (NES58) strains carrying the acrAB-lac transcriptional fusion. Cells were grown in LB medium (control) or LB medium supplemented with 0.25 mm cholic acid, 0.25 mm deoxycholic acid, or 0.25 mm bile salts. The data correspond to mean values from three independent experiments. Bars correspond to the standard deviation. Student's t test; *, p < 0.01 versus WT.

Mentions: acrAB Activation by Bile Is Dependent on the RamA Regulator—The AcrAB pump is reported to export bile salts and play a role in bile resistance in E. coli and Salmonella (44-46). Also, acrAB is reportedly induced by bile in a Robdependent manner in E. coli (31). Although acrAB is also induced by bile in Salmonella, the induction mediating regulator is unknown (47). Prouty et al. (47) further reported that acrAB activation by bile is independent of MarA, Rob, PhoP/PhoQ, and RpoS. We investigated the possibility that RamA controls acrAB expression in response to bile. In agreement with Prouty et al. (47), bile salts, cholic acid, and deoxycholic acid significantly induced acrAB expression in Salmonella (Fig. 3). When ramA was deleted, acrAB induction was eliminated (Fig. 3). These findings indicate a novel RamA-dependent pathway for bile-mediated regulation of the AcrAB efflux pump in Salmonella, different from that observed in E. coli.


AcrAB multidrug efflux pump regulation in Salmonella enterica serovar Typhimurium by RamA in response to environmental signals.

Nikaido E, Yamaguchi A, Nishino K - J. Biol. Chem. (2008)

Requirement of RamA for induction of acrAB by bile. β-Galactosidase levels were assayed in WT (NKS505) or ΔramA (NES58) strains carrying the acrAB-lac transcriptional fusion. Cells were grown in LB medium (control) or LB medium supplemented with 0.25 mm cholic acid, 0.25 mm deoxycholic acid, or 0.25 mm bile salts. The data correspond to mean values from three independent experiments. Bars correspond to the standard deviation. Student's t test; *, p < 0.01 versus WT.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2527123&req=5

fig3: Requirement of RamA for induction of acrAB by bile. β-Galactosidase levels were assayed in WT (NKS505) or ΔramA (NES58) strains carrying the acrAB-lac transcriptional fusion. Cells were grown in LB medium (control) or LB medium supplemented with 0.25 mm cholic acid, 0.25 mm deoxycholic acid, or 0.25 mm bile salts. The data correspond to mean values from three independent experiments. Bars correspond to the standard deviation. Student's t test; *, p < 0.01 versus WT.
Mentions: acrAB Activation by Bile Is Dependent on the RamA Regulator—The AcrAB pump is reported to export bile salts and play a role in bile resistance in E. coli and Salmonella (44-46). Also, acrAB is reportedly induced by bile in a Robdependent manner in E. coli (31). Although acrAB is also induced by bile in Salmonella, the induction mediating regulator is unknown (47). Prouty et al. (47) further reported that acrAB activation by bile is independent of MarA, Rob, PhoP/PhoQ, and RpoS. We investigated the possibility that RamA controls acrAB expression in response to bile. In agreement with Prouty et al. (47), bile salts, cholic acid, and deoxycholic acid significantly induced acrAB expression in Salmonella (Fig. 3). When ramA was deleted, acrAB induction was eliminated (Fig. 3). These findings indicate a novel RamA-dependent pathway for bile-mediated regulation of the AcrAB efflux pump in Salmonella, different from that observed in E. coli.

Bottom Line: Among these pumps, AcrAB is effective in generating drug resistance and has wide substrate specificity.Other regulators of acrAB such as MarA, SoxS, Rob, SdiA, and AcrR did not contribute to acrAB induction by indole in Salmonella.Our results suggest that RamA controls the Salmonella AcrAB-TolC multidrug efflux system through dual regulatory modes in response to environmental signals.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Membrane Biology, Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan.

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.

Show MeSH
Related in: MedlinePlus