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Journal of Bacteriology, April 2000, p. 1872-1882, Vol. 182, No. 7
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Multiple Factors Independently Regulate hilA and Invasion Gene Expression in Salmonella enterica Serovar Typhimurium

Robin L. Lucas,1 C. Phoebe Lostroh,1 Concetta C. DiRusso,2 Michael P. Spector,3 Barry L. Wanner,4 and Catherine A. Lee1,*

Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 021151; Department of Biochemistry and Molecular Biology, The Albany Medical College, Albany, New York 122082; Department of Biomedical Sciences, University of South Alabama, Mobile, Alabama 366883; and Department of Biological Sciences, Purdue University, West Lafayette, Indiana 479074

Received 11 November 1999/Accepted 19 January 2000

HilA activates the expression of Salmonella enterica serovar Typhimurium invasion genes. To learn more about regulation of hilA, we isolated Tn5 mutants exhibiting reduced hilA and/or invasion gene expression. In addition to expected mutations, we identified Tn5 insertions in pstS, fadD, flhD, flhC, and fliA. Analysis of the pstS mutant indicates that hilA and invasion genes are repressed by the response regulator PhoB in the absence of the Pst high-affinity inorganic phosphate uptake system. This system is required for negative control of the PhoR-PhoB two-component regulatory system, suggesting that hilA expression may be repressed by PhoR-PhoB under low extracellular inorganic phosphate conditions. FadD is required for uptake and degradation of long-chain fatty acids, and our analysis of the fadD mutant indicates that hilA is regulated by a FadD-dependent, FadR-independent mechanism. Thus, fatty acid derivatives may act as intracellular signals to regulate hilA expression. flhDC and fliA encode transcription factors required for flagellum production, motility, and chemotaxis. Complementation studies with flhC and fliA mutants indicate that FliZ, which is encoded in an operon with fliA, activates expression of hilA, linking regulation of hilA with motility. Finally, epistasis tests showed that PhoB, FadD, FliZ, SirA, and EnvZ act independently to regulate hilA expression and invasion. In summary, our screen has identified several distinct pathways that can modulate S. enterica serovar Typhimurium's ability to express hilA and invade host cells. Integration of signals from these different pathways may help restrict invasion gene expression during infection.

* Corresponding author. Mailing address: Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Ave., Boston, MA 02115. Phone: (617) 432-4988. Fax: (617) 738-7664. E-mail: clee{at}hms.harvard.edu.

Journal of Bacteriology, April 2000, p. 1872-1882, Vol. 182, No. 7
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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