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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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Effect of indole and bile on ramA transcription. β-Galactosidase levels were assayed in the WT strain carrying the ramA reporter plasmid (pNNramA) (NES84). Cells were grown in LB medium supplemented with 2 mm indole, 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 control.
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fig9: Effect of indole and bile on ramA transcription. β-Galactosidase levels were assayed in the WT strain carrying the ramA reporter plasmid (pNNramA) (NES84). Cells were grown in LB medium supplemented with 2 mm indole, 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 control.

Mentions: Indole Induces ramA Expression but Bile Does Not—The effects of indole and bile on ramA expression levels were investigated because increased ramA expression has been reported to cause increased production of the AcrAB-TolC efflux system (49). Using a reporter plasmid of ramA, a β-galactosidase assay showed that indole enhanced the promoter activity of ramA (Fig. 9). This suggests that indole induces acrAB through increased expression of ramA. Bile salts, cholic acid, and deoxycholic acid did not affect the expression level of ramA despite its requirement for induction of acrAB. This indicates an acrAB regulatory mode other than through increased production of RamA.


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)

Effect of indole and bile on ramA transcription. β-Galactosidase levels were assayed in the WT strain carrying the ramA reporter plasmid (pNNramA) (NES84). Cells were grown in LB medium supplemented with 2 mm indole, 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 control.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig9: Effect of indole and bile on ramA transcription. β-Galactosidase levels were assayed in the WT strain carrying the ramA reporter plasmid (pNNramA) (NES84). Cells were grown in LB medium supplemented with 2 mm indole, 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 control.
Mentions: Indole Induces ramA Expression but Bile Does Not—The effects of indole and bile on ramA expression levels were investigated because increased ramA expression has been reported to cause increased production of the AcrAB-TolC efflux system (49). Using a reporter plasmid of ramA, a β-galactosidase assay showed that indole enhanced the promoter activity of ramA (Fig. 9). This suggests that indole induces acrAB through increased expression of ramA. Bile salts, cholic acid, and deoxycholic acid did not affect the expression level of ramA despite its requirement for induction of acrAB. This indicates an acrAB regulatory mode other than through increased production of RamA.

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