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Infection and Immunity, November 2009, p. 5107-5115, Vol. 77, No. 11
0019-9567/09/$08.00+0     doi:10.1128/IAI.00759-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Codependent and Independent Effects of Nitric Oxide-Mediated Suppression of PhoPQ and Salmonella Pathogenicity Island 2 on Intracellular Salmonella enterica Serovar Typhimurium Survival{triangledown}

Travis J. Bourret,{dagger} Miryoung Song, and Andrés Vázquez-Torres*

Department of Microbiology, University of Colorado Denver School of Medicine, Aurora, Colorado

Received 6 July 2009/ Returned for modification 11 August 2009/ Accepted 28 August 2009

Here we show that the Salmonella enterica serovar Typhimurium PhoQ sensor kinase lessens the cytotoxicity of reactive nitrogen species (RNS) generated by inducible nitric oxide synthase (iNOS) in the innate response of mononuclear phagocytic cells. This observation is consistent with the expression patterns of PhoP-activated genes during moderate nitrosative stress in the innate host response. In contrast, RNS synthesized during high-NO fluxes of gamma interferon (IFN-{gamma})-activated macrophages repress PhoP-activated lpxO, pagP, and phoP gene transcription. Because PhoP-regulated Salmonella pathogenicity island 2 (SPI2) genes are also repressed by high-order RNS (39), we investigated whether the NO-mediated inhibition of PhoPQ underlies the repression of SPI2. Our studies indicate that a third of the expression of the SPI2 spiC gene recorded in nonactivated macrophages depends on PhoQ. Transcription of spiC is repressed in IFN-{gamma}-primed macrophages in an iNOS-dependent manner, irrespective of the phoQ status of the bacteria. Transcription of spiC is restored in IFN-{gamma}-treated, iNOS-deficient macrophages to levels sustained by a phoQ mutant in nonactivated phagocytes, suggesting that most NO-dependent repression of spiC is due to the inhibition of PhoPQ-independent targets. Comparison of the intracellular fitness of spiC, phoQ, and spiC phoQ mutants revealed that PhoPQ and SPI2 have codependent and independent effects on S. Typhimurium survival during innate nitrosative stress. However, the intracellular survival of most S. Typhimurium bacteria is conferred by the PhoPQ two-component regulator, and the SPI2 type III secretion system is repressed by high-order RNS of IFN-{gamma}-activated macrophages.

* Corresponding author. Mailing address: Department of Microbiology, University of Colorado at Denver School of Medicine, Mail Stop 8333, P.O. Box 6511, Aurora, CO 80045. Phone: (303) 724-4218. Fax: (303) 724-4226. E-mail: andres.vazquez-torres{at}ucdenver.edu

{triangledown} Published ahead of print on 8 September 2009.

Editor: A. J. Bäumler

{dagger} Present address: Laboratory of Zoonotic Pathogens, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 903 S. 4th St., Hamilton, MT 59840.

Infection and Immunity, November 2009, p. 5107-5115, Vol. 77, No. 11
0019-9567/09/$08.00+0     doi:10.1128/IAI.00759-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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