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σB is an alternative σ factor that regulates stress response and virulence genes in the foodborne pathogen Listeria monocytogenes. To gain further insight into σB-dependent regulatory mechanisms in L. monocytogenes, we (i) performed quantitative proteomic comparisons between the L. monocytogenes parent strain 10403S and an isogenic ΔsigB mutant and (ii) conducted a meta-analysis of published microarray studies on the 10403S σB regulon. A total of 134 genes were found to be significantly positively regulated by σB at the transcriptomic level with >75 % of these genes preceded by putative σB-dependent promoters; 21 of these 134 genes were also found to be positively regulated by σB through proteomics. In addition, 15 proteins were only found to be positively regulated by σB through proteomics analyses, including Lmo1349, a putative glycine cleavage system protein. The lmo1349 gene is preceded by a 5′ UTR that functions as a glycine riboswitch, which suggests regulation of glycine metabolism by σB in L. monocytogenes. Herein, we propose a model where σB upregulates pathways that facilitate biosynthesis and uptake of glycine, which may then activate this riboswitch. Our data also (i) identified a number of σB-dependent proteins that appear to be encoded by genes that are co-regulated by multiple transcriptional regulators, in particular PrfA, and (ii) found σB-dependent genes and proteins to be overrepresented in the ‘energy metabolism’ role category, highlighting contributions of the σB regulon to L. monocytogenes energy metabolism as well as a role of PrfA and σB interaction in regulating aspects of energy metabolism in L. monocytogenes.
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