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Applied and Environmental Microbiology, December 2007, p. 7981-7991, Vol. 73, No. 24
0099-2240/07/$08.00+0     doi:10.1128/AEM.01281-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Transcriptomic and Phenotypic Analyses Suggest a Network between the Transcriptional Regulators HrcA and ^B in Listeria monocytogenes ^,

Yuewei Hu, Haley F. Oliver, Sarita Raengpradub, M. Elizabeth Palmer, Renato H. Orsi, Martin Wiedmann, and Kathryn J. Boor^*

Department of Food Science, Cornell University, Ithaca, New York

Received 9 June 2007/ Accepted 16 October 2007

Listeria monocytogenes HrcA and CtsR negatively regulate class I and III stress response genes, respectively, while ^B positively regulates the transcription of class II stress response genes. To define the HrcA regulon and identify interactions between HrcA, CtsR, and ^B, we characterized newly generated L. monocytogenes hrcA, ctsR hrcA, and hrcA sigB strains, along with previously described sigB, ctsR, and ctsR sigB strains, using phenotypic assays (i.e., heat resistance, acid resistance, and invasion of human intestinal epithelial cells) and performed whole-genome transcriptome analysis of the hrcA strain. The hrcA and sigB deletions had significant effects on heat resistance. While the hrcA deletion had no significant effect on acid resistance or invasion efficiency in Caco-2 cells, a linear regression model revealed a significant (P = 0.0493) effect of interactions between the hrcA deletion and the ctsR deletion on invasiveness. Microarray-based transcriptome analyses and promoter searches identified (i) 25 HrcA-repressed genes, including two operons (the groESL and dnaK operons, both confirmed as HrcA regulated by quantitative real-time PCR) and one gene directly repressed by HrcA, and (ii) 36 genes that showed lower transcript levels in the hrcA strain and thus appear to be indirectly upregulated by HrcA. A number of genes were found to be coregulated by either HrcA and CtsR (2 genes), HrcA and ^B (31 genes), or all three regulators (5 genes, e.g., gadCB). Combined with previous evidence that ^B appears to directly regulate hrcA transcription, our data suggest that HrcA and ^B, as well as CtsR, form a regulatory network that contributes to the transcription of a number of L. monocytogenes genes.

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* Corresponding author. Mailing address: Department of Food Science, 413 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 26 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. 7981-7991, Vol. 73, No. 24
0099-2240/07/$08.00+0     doi:10.1128/AEM.01281-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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