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Applied and Environmental Microbiology, November 2002, p. 5408-5416, Vol. 68, No. 11
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.11.5408-5416.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Low-Shear Modeled Microgravity Alters the Salmonella enterica Serovar Typhimurium Stress Response in an RpoS-Independent Manner

Program in Molecular Pathogenesis and Immunity, Department of Microbiology and Immunology, Tulane University School of Medicine, New Orleans, Louisiana 70112,¹ EASI/Wyle Laboratories,² Life Sciences Research Laboratories, National Aeronautics and Space Administration-Johnson Space Center, Houston, Texas 77058,⁴ Sidney Kimmel Cancer Center, San Diego, California 92121³

Received 8 May 2002/ Accepted 27 August 2002

We have previously demonstrated that low-shear modeled microgravity (low-shear MMG) serves to enhance the virulence of a bacterial pathogen, Salmonella enterica serovar Typhimurium. The Salmonella response to low-shear MMG involves a signaling pathway that we have termed the low-shear MMG stimulon, though the identities of the low-shear MMG stimulon genes and regulatory factors are not known. RpoS is the primary sigma factor required for the expression of genes that are induced upon exposure to different environmental-stress signals and is essential for virulence in mice. Since low-shear MMG induces a Salmonella acid stress response and enhances Salmonella virulence, we reasoned that RpoS would be a likely regulator of the Salmonella low-shear MMG response. Our results demonstrate that low-shear MMG provides cross-resistance to several environmental stresses in both wild-type and isogenic rpoS mutant strains. Growth under low-shear MMG decreased the generation time of both strains in minimal medium and increased the ability of both strains to survive in J774 macrophages. Using DNA microarray analysis, we found no evidence of induction of the RpoS regulon by low-shear MMG but did find that other genes were altered in expression under these conditions in both the wild-type and rpoS mutant strains. Our results indicate that, under the conditions of these studies, RpoS is not required for transmission of the signal that induces the low-shear MMG stimulon. Moreover, our studies also indicate that low-shear MMG can be added to a short list of growth conditions that can serve to preadapt an rpoS mutant for resistance to multiple environmental stresses.

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