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Journal of Bacteriology, December 2007, p. 8447-8457, Vol. 189, No. 23
0021-9193/07/$08.00+0     doi:10.1128/JB.01198-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

The RcsCDB Signaling System and Swarming Motility in Salmonella enterica Serovar Typhimurium: Dual Regulation of Flagellar and SPI-2 Virulence Genes ^,

Section of Molecular Genetics and Microbiology & Institute of Cellular and Molecular Biology, University of Texas at Austin, Austin, Texas 78712,¹ Department of Statistics, University of Connecticut, Storrs, Connecticut 06269,² Sidney Kimmel Cancer Center, 10835 Altman Row, San Diego, California 92121³

Received 26 July 2007/ Accepted 14 September 2007

The Rcs phosphorelay is a multicomponent signaling system that positively regulates colanic acid synthesis and negatively regulates motility and virulence. We have exploited a spontaneously isolated mutant, IgaA(T191P), that is nearly maximally activated for the Rcs system to identify a vast set of genes that respond to the stimulation, and we report new regulatory properties of this signaling system in Salmonella enterica serovar Typhimurium. Microarray data show that the Rcs system normally functions as a positive regulator of SPI-2 and other genes important for the growth of Salmonella in macrophages, although when highly activated the system completely represses the SPI-1/SPI-2 virulence, flagellar, and fimbrial biogenesis pathways. The auxiliary protein RcsA, which works with RcsB to positively regulate colanic acid and other target genes, not only stimulates but also antagonizes the positive regulation of many genes in the igaA mutant. We show that RcsB represses motility through the RcsB box in the promoter region of the master operon flhDC and that RcsA is not required for this regulation. Curiously, RcsB selectively stimulates expression of the flagellar type 3 secretion genes fliPQR; an RcsAB box located downstream of fliR influences this regulation. We show that excess colanic acid impairs swimming and inhibits swarming motility, consistent with the inverse regulation of the two pathways by the Rcs system.

Published ahead of print on 28 September 2007.

Supplemental material for this article may be found at http://jb.asm.org/.

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