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Journal of Bacteriology, September 2003, p. 5096-5108, Vol. 185, No. 17
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.17.5096-5108.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

RtsA and RtsB Coordinately Regulate Expression of the Invasion and Flagellar Genes in Salmonella enterica Serovar Typhimurium

Craig D. Ellermeier1 and James M. Slauch1,2*

Department of Microbiology,1 College of Medicine, University of Illinois, Urbana, Illinois 618012

Received 14 March 2003/ Accepted 27 May 2003

Salmonella enterica serovar Typhimurium encounters numerous host environments and defense mechanisms during the infection process. The bacterium responds by tightly regulating the expression of virulence genes. We identified two regulatory proteins, termed RtsA and RtsB, which are encoded in an operon located on an island integrated at tRNAPheU in S. enterica serovar Typhimurium. RtsA belongs to the AraC/XylS family of regulators, and RtsB is a helix-turn-helix DNA binding protein. In a random screen, we identified five RtsA-regulated fusions, all belonging to the Salmonella pathogenicity island 1 (SPI1) regulon, which encodes a type III secretion system (TTSS) required for invasion of epithelial cells. We show that RtsA increases expression of the invasion genes by inducing hilA expression. RtsA also induces expression of hilD, hilC, and the invF operon. However, induction of hilA is independent of HilC and HilD and is mediated by direct binding of RtsA to the hilA promoter. The phenotype of an rtsA null mutation is similar to the phenotype of a hilC mutation, both of which decrease expression of SPI1 genes approximately twofold. We also show that RtsA can induce expression of a SPI1 TTSS effector, slrP, independent of any SPI1 regulatory protein. RtsB represses expression of the flagellar genes by binding to the flhDC promoter region. Repression of the positive activators flhDC decreases expression of the entire flagellar regulon. We propose that RtsA and RtsB coordinate induction of invasion and repression of motility in the small intestine.

* Corresponding author. Mailing address: Department of Microbiology, University of Illinois, B103 Chemical and Life Sciences Laboratory, 601 S. Goodwin Ave., Urbana, IL 61801. Phone: (217) 244-1956. Fax: (217) 244-6697. E-mail: slauch{at}uiuc.edu.

Journal of Bacteriology, September 2003, p. 5096-5108, Vol. 185, No. 17
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.17.5096-5108.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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