Phosphotransferase System-Dependent Extracellular Growth of Listeria monocytogenes Is Regulated by Alternative Sigma Factors σLand σH

Alternative sigma (σ) factors and phosphotransferase systems (PTSs) play pivotal roles in the environmental adaptation and virulence ofListeria monocytogenes . The growth of theL. monocytogenes parent strain 10403S and 15 isogenic alternative σ factor mutants was assessed in defined minimal medium (DM) with PTS-dependent or non-PTS-dependent carbon sources at 25°C or 37°C. Overall, our results suggested that the regulatory effect of alternative σ factors on the growth ofL. monocytogenes is dependent on the temperature and the carbon source. One-way analysis of variance (one-way ANOVA) showed that the factor “strain” had a significant effect on the maximum growth rate (μmax ), lag phase duration (λ), and maximum optical density (ODmax ) in PTS-dependent carbon sources (P < 0.05) but not in a non-PTS-dependent carbon source. Also, the ODmax was not affected by strain for any of the three PTS-dependent carbon sources at 25°C but was affected by strain at 37°C. Monitoring by quantitative real-time PCR (qRT-PCR) showed that transcript levels forlmo0027 , a glucose-glucoside PTS permease (PTSGlc -1)-encoding gene, were higher in the absence of σL , and lower in the absence of σH , than in the parent strain. Our data thus indicate that σL negatively regulateslmo0027 and that the increased μmax observed for the ΔsigL strain in DM with glucose may be associated with increased expression of PTSGlc -1 encoded bylmo0027 . Our findings suggest that σH and σL mediate the PTS-dependent growth ofL. monocytogenes through complex transcriptional regulations and fine-tuning of the expression of specificpts genes, includinglmo0027 . Our findings also reveal a more important and complex role of alternative σ factors in the regulation of growth in different sugar sources than previously assumed.