monocytogenes. Results and discussion OICR-9429 concentration Proteomic comparisons between L. monocytogenes mutants expressing only σL, σH, and σC and a quadruple mutant that does not express any alternative σ factors, all grown to stationary phase at 37°C, showed that (i) σH provides, among these three alternative σ factors, positive regulation for the largest number of proteins, consistent with previous transcriptomic studies [7]; (ii) σL appears to contribute

to negative regulation of a number of proteins; (iii) σC regulates a small number of proteins in L. monocytogenes grown to stationary phase at 37°C; and (iv) proteins regulated by multiple alternative σ factors include MptA, which has a potential role in regulation of PrfA. σH positively regulates a large number of proteins and appears to directly and indirectly contribute to transport and metabolism of β-glucosides Our proteomic comparison identified 15 proteins as positively regulated by σH, as supported by higher protein levels (Fold change (FC) ≥ 1.5; p-valuec (p c) < 0.05) in L. monocytogenes ΔBCL as compared to the ΔBCHL strain (Table 1); four of these 15 proteins also showed higher levels in the parent strain (which expresses

all four alternative σ factors) as compared to the quadruple mutant. Overall, positive fold changes for these proteins (in ΔBCL versus ΔBCHL) ranged from 1.55 to 3.39. These 15 proteins represented nine role categories (e.g., “energy metabolism”; SIS3 in vivo “amino acid biosynthesis”; “transport and binding proteins”, see Figure 1); a Monte Carlo simulation of Fisher’s exact test did not find a significant association between positively regulated genes and role categories (p = 0.06); however, individual Fisher’s exact tests did show overrepresentation of proteins in the role find more category “amino acid biosynthesis” among the 15 proteins that were found to be positively regulated by σH Glutamate dehydrogenase (with a significant p-value; p < 0.01; Odds Ratio = 6.26). Some of the 15 proteins positively regulated by σH have likely roles in stress adaptation and

virulence, including Lmo1439 (superoxide dismutase, SodA) [24] and Lmo0096 (mannose-specific PTS system IIAB component, MptA), which has been linked to regulation of the virulence gene regulator PrfA [25]. Previously reported transcriptomic studies [7] only identified the coding gene for one of these 15 proteins (i.e., Lmo1454) as σH-dependent; lmo1454 (rpoD) was also identified as preceded by a σH consensus promoter, suggesting direct transcriptional regulation by σH. In addition, the coding gene for Lmo2487, one of these 15 proteins, is in an operon with lmo2485, which was previously reported to be positively regulated by σH, even though no upstream σH consensus promoter was identified, suggesting indirect regulation [7].