SigmaB-dependent and sigmaB-independent mechanisms contribute to transcription of Listeria monocytogenes cold stress genes during cold shock and cold growth.

The role of the stress response regulator sigma(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 DeltasigB mutant, which were either cold shocked at 4 degrees C in brain heart infusion (BHI) broth for up to 30 min or grown at 4 degrees C in BHI for 12 days. Transcript levels of the housekeeping genes rpoB and gap, the sigma(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 sigma(B)-dependent transcription, which necessitated the use of centrifugation-independent protocols to evaluate the contributions of sigma(B) to transcription during cold shock. Our data confirmed that transcription of the cold stress genes ltrC and fri is at least partially sigma(B) dependent and experimentally identified a sigma(B)-dependent ltrC promoter. In addition, our data indicate that (i) while sigma(B) activity is induced during 30 min of cold shock, this cold shock does not induce the transcription of sigma(B)-dependent or -independent cold shock genes; (ii) sigma(B) is not required for L. monocytogenes growth at 4 degrees C in BHI; and (iii) transcription of the putative cold stress genes opuCA, fri, and oppA is sigma(B) independent during growth at 4 degrees C, while both bsh and ltrC show growth phase and sigma(B)-dependent transcription during growth at 4 degrees C. We conclude that sigma(B)-dependent and sigma(B)-independent mechanisms contribute to the ability of L. monocytogenes to survive and grow at low temperatures.