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Appl. Environ. Microbiol. doi:10.1128/AEM.00714-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

^B-dependent and -independent mechanisms contribute to transcription of Listeria monocytogenes cold stress genes during cold shock and cold growth

Department of Food Science, Cornell University, Ithaca, NY 14853 USA

^* To whom correspondence should be addressed. Email: mw16{at}cornell.edu.

	Abstract

The role of the stress response regulator ^B (encoded by sigB) in directing expression of selected putative and confirmed cold response genes was evaluated using Listeria monocytogenes 10403S and an isogenic sigB mutant, which were either cold shocked at 4°C in brain heart infusion (BHI) broth for up to 30 minutes or grown at 4°C in BHI for 12 days. Transcript levels of the housekeeping genes rpoB and gap, the ^B-dependent genes opuCA and bsh, and the cold stress genes ltrC, oppA and fri were measured using quantitative reverse transcriptase PCR. Transcriptional start sites for ltrC, oppA, and fri were determined using RACE-PCR. Centrifugation was found to rapidly induce ^B-dependent transcription, which necessitated the use of centrifugation-independent protocols to evaluate contributions of ^B to transcription during cold shock. Our data confirmed that transcription of the cold stress genes ltrC and fri is at least partially ^B-dependent and experimentally identified a ^B-dependent ltrC promoter. In addition, our data indicate (i) while ^B activity is induced during 30 minutes of cold shock, this cold shock does not induce transcription of ^B-dependent or -independent cold shock genes; (ii) ^B is not required for L. monocytogenes growth at 4°C in BHI; and (iii) transcription of the putative cold stress genes opuCA, fri, and oppA is ^B-independent during growth at 4°C, while both bsh and ltrC show growth phase and ^B-dependent transcription during growth at 4°C. We conclude that ^B-dependent and -independent mechanisms contribute to the ability of L. monocytogenes to survive and grow at low temperatures.

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