σ B -Dependent and σ B -Independent Mechanisms Contribute to Transcription of Listeria monocytogenes Cold Stress Genes during Cold Shock and Cold Growth

Abstract

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