Comparative Analysis of the σ B -Dependent Stress Responses in Listeria monocytogenes and Listeria innocua Strains Exposed to Selected Stress Conditions

Abstract

ABSTRACT The alternative sigma factor σ B contributes to transcription of stress response and virulence genes in diverse gram-positive bacterial species. The composition and functions of the Listeria monocytogenes and Listeria innocua σ B regulons were hypothesized to differ due to virulence differences between these closely related species. Transcript levels in stationary-phase cells and in cells exposed to salt stress were characterized by microarray analyses for both species. In L. monocytogenes , 168 genes were positively regulated by σ B ; 145 of these genes were preceded by a putative σ B consensus promoter. In L. innocua , 64 genes were positively regulated by σ B . σ B contributed to acid stress survival in log-phase cells for both species but to survival in stationary-phase cells only for L. monocytogenes . In summary, (i) the L. monocytogenes σ B regulon includes >140 genes that are both directly and positively regulated by σ B , including genes encoding proteins with importance in stress response, virulence, transcriptional regulation, carbohydrate metabolism, and transport; (ii) a number of L. monocytogenes genes encoding flagellar proteins show higher transcript levels in the Δ sigB mutant, and both L. monocytogenes and L. innocua Δ sigB null mutants have increased motility compared to the respective isogenic parent strains, suggesting that σ B affects motility and chemotaxis; and (iii) although L. monocytogenes and L. innocua differ in σ B -dependent acid stress resistance and have species-specific σ B -dependent genes, the L. monocytogenes and L. innocua σ B regulons show considerable conservation, with a common set of at least 49 genes that are σ B dependent in both species.