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Science  27 Feb 2009:
Vol. 323, Issue 5918, pp. 1148c-1149c
DOI: 10.1126/science.323.5918.1148c

Salmonella species live in a diverse range of hosts and environments and transfer readily between them. This lineage has evolved in a stepwise manner into multiple strains of pathogens as a result of the snatch and grab of mobile elements called pathogenicity islands from other bacterial species. A sensor kinase and response regulator pair of components on one of the islands acts as an antenna for environmental changes. Depending on the signals it receives, this antenna orchestrates expression across virulence genes by binding to their respective cis-regulatory elements, wherever they are in the genome. Thus, environmental cues can be matched to niche-specific gene expression. Osborne et al. confirmed the evolutionary significance of cis regulation for Salmonella enterica by a series of in vivo competition experiments between mutants allowed to infect mice. Mutations in regulatory elements enable a bacterium to thrive opportunistically in multiple and contrasting niches without feeling too much pain from conflicting selection pressures on its genome. — CA

Proc. Natl. Acad. Sci. U.S.A. 106, 10.1073/pnas.0811669106 (2009).

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