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Applied and Environmental Microbiology, December 2007, p. 7967-7980, Vol. 73, No. 24
0099-2240/07/$08.00+0     doi:10.1128/AEM.01085-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Phenotypic and Transcriptomic Analyses Demonstrate Interactions between the Transcriptional Regulators CtsR and Sigma B in Listeria monocytogenes ^,

Yuewei Hu,¹ Sarita Raengpradub,¹ Ute Schwab,^1,2 Chris Loss,¹ Renato H. Orsi,¹ Martin Wiedmann,¹ and Kathryn J. Boor^1*

Department of Food Science,¹ Department of Microbiology and Immunology, Cornell University, Ithaca, New York²

Received 15 May 2007/ Accepted 7 October 2007

Listeria monocytogenes ^B positively regulates the transcription of class II stress response genes; CtsR negatively regulates class III stress response genes. To identify interactions between these two stress response systems, we constructed L. monocytogenes ctsR and ctsR sigB strains, as well as a ctsR strain expressing ctsR in trans under the control of an IPTG (isopropyl-β-D-thiogalactopyranoside)-inducible promoter. These strains, along with a parent and a sigB strain, were assayed for motility, heat resistance, and invasion of human intestinal epithelial cells, as well as by whole-genome transcriptomic and quantitative real-time PCR analyses. Both ctsR and ctsR sigB strains had significantly higher thermotolerances than the parent strain; however, full heat sensitivity was restored to the ctsR strain when ctsR was expressed in trans. Although log-phase ctsR was not reduced in its ability to infect human intestinal cells, the ctsR sigB strain showed significantly lower invasion efficiency than either the parent strain or the sigB strain, indicating that interactions between CtsR and ^B contribute to invasiveness. Statistical analyses also confirmed interactions between the ctsR and the sigB null mutations in both heat resistance and invasion phenotypes. Microarray transcriptomic analyses and promoter searches identified (i) 42 CtsR-repressed genes, (ii) 22 genes with lower transcript levels in the ctsR strain, and (iii) at least 40 genes coregulated by both CtsR and ^B, including genes encoding proteins with confirmed or plausible roles in virulence and stress response. Our data demonstrate that interactions between CtsR and ^B play an important role in L. monocytogenes stress resistance and virulence.

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* Corresponding author. Mailing address: Department of Food Science, 412 Stocking Hall, Cornell University, Ithaca, NY 14853. Phone: (607) 255-3111. Fax: (607) 254-4868. E-mail: kjb4{at}cornell.edu

Published ahead of print on 12 October 2007.

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

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Applied and Environmental Microbiology, December 2007, p. 7967-7980, Vol. 73, No. 24
0099-2240/07/$08.00+0     doi:10.1128/AEM.01085-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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