Effects of Growth Phase and Temperature onσBActivity within aListeria monocytogenesPopulation: Evidence for RsbV-Independent Activation ofAuthor(s) - Marta Utratna, Eoin F. J. Cosgrave, Claas Baustian, Rhodri Ceredig, Conor P. O’Byrne

The alternative sigma factor σ B of Listeria monocytogenes is responsible for regulating the transcription of many of the genes necessary for adaptation to both food-related stresses and to conditions found within the gastrointestinal tract of the host. The present study sought to investigate the influence of growth phase and temperature on the activation of σ B within populations of L . monocytogenes EGD-e wild-type, Δ sigB, and Δ rsbV throughout growth at both 4°C and 37°C, using a reporter fusion that couples expression of EGFP to the strongly σ B -dependent promoter of lmo 2230. A similar σ B activation pattern within the population was observed in wt- egfp at both temperatures, with the highest induction of σ B occurring in the early exponential phase of growth when the fluorescent population rapidly increased, eventually reaching the maximum in early stationary phase. Interestingly, induction of σ B activity was heterogeneous, with only a proportion of the cells in the wt- egfp population being fluorescent above the background autofluorescence level. Moreover, significant RsbV-independent activation of σ B was observed during growth at 4°C. This result suggests that an alternative route to σ B activation exists in the absence of RsbV, a finding that is not explained by the current model for σ B regulation.