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Journal of Bacteriology, February 2004, p. 910-918, Vol. 186, No. 4
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.4.910-918.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

H-NS Represses Salmonella enterica Serovar Typhimurium dsbA Expression during Exponential Growth

C. V. Gallant,^1, T. Ponnampalam,^1, H. Spencer,¹ J. C. D. Hinton,² and N. L. Martin^1*

Department of Microbiology and Immunology, Queen's University, Kingston, Ontario, Canada K7L 3N6,¹ Institute of Food Research, Norwich Research Park, Norwich NR4 7UA, England²

Received 30 July 2003/ Accepted 3 October 2003

Disulfide bond formation catalyzed by disulfide oxidoreductases occurs in the periplasm and plays a major role in the proper folding and integrity of many proteins. In this study, we were interested in elucidating factors that influence the regulation of dsbA, a gene coding for the primary disulfide oxidoreductase found in Salmonella enterica serovar Typhimurium. Strains with mutations created by transposon mutagenesis were screened for strains with altered expression of dsbA. A mutant (NLM2173) was found where maximal expression of a dsbA::lacZ transcriptional fusion occurred in the exponential growth phase in contrast to that observed in the wild type where maximal expression occurs in stationary phase. Sequence analysis of NLM2173 demonstrated that the transposon had inserted upstream of the gene encoding H-NS. Western immunoblot analysis using H-NS and StpA antibodies showed decreased amounts of H-NS protein in NLM2173, and this reduction in H-NS correlated with an increase of StpA protein. Northern blot analysis with a dsbA-specific probe showed an increase in dsbA transcript during exponential phase of growth. Direct binding of H-NS to the dsbA promoter region was verified using purified H-NS in electrophoretic mobility shift assays. Thus, a reduction in H-NS protein is correlated with a derepression of dsbA in NLM2173, suggesting that H-NS normally plays a role in suppressing the expression of dsbA during exponential phase growth.

C.V.G. and T.P. contributed equally to the work presented in this report.

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