ABSTRACTThe role of the stress response regulator σB(encoded bysigB) in directing the expression of selected putative and confirmed cold response genes was evaluated usingListeria monocytogenes10403S and an isogenic ΔsigBmutant, 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 genesrpoBandgap, the σB-dependent genesopuCAandbsh, and the cold stress genesltrC, oppA, andfriwere measured using quantitative reverse transcriptase PCR. Transcriptional start sites forltrC, oppA, andfriwere determined using rapid amplification of cDNA ends PCR. Centrifugation was found to rapidly induce σB-dependent transcription, which necessitated the use of centrifugation-independent protocols to evaluate the contributions of σBto transcription during cold shock. Our data confirmed that transcription of the cold stress genesltrCandfriis at least partially σBdependent and experimentally identified a σB-dependentltrCpromoter. In addition, our data indicate that (i) while σBactivity is induced during 30 min of cold shock, this cold shock does not induce the transcription of σB-dependent or -independent cold shock genes; (ii) σBis not required forL. monocytogenesgrowth at 4°C in BHI; and (iii) transcription of the putative cold stress genesopuCA, fri, andoppAis σBindependent during growth at 4°C, while bothbshandltrCshow growth phase and σB-dependent transcription during growth at 4°C. We conclude that σB-dependent and σB-independent mechanisms contribute to the ability ofL. monocytogenesto survive and grow at low temperatures.