(2011) identified three different genes, representing two operons (lmo1854; lmo2185 and lmo2186), that showed lower transcript levels in the parent strain compared to the ΔsigC mutant, suggesting negative regulation by σC[7]. While our data are consistent with previous

findings of a limited σC this website regulon in L. monocytogenes 10403S, it is possible that σC- dependent gene regulation only occurs under specific conditions (e.g., heat stress [3]) and that more complete identification of the σC regulon requires transcriptomic and proteomic studies under specific conditions that remain to be defined. In addition, future experiments using an L. monocytogenes strain that expresses sigC from an inducible promoter may also allow for identification of additional proteins that show σC-dependent production; this strategy applied to other alternative σ factors may also allow for MAPK inhibitor identification of additional proteins that

show σH- or σL-dependent production. Proteins regulated by multiple alternative σ factors include MptA, which has a potential role in regulation VS-4718 nmr of PrfA Our data reported here also provided an opportunity to gather further insight into genes and proteins that are co-regulated by multiple σ factors and, consequently, into regulatory networks among different alternative σ factors. To facilitate these analyses, we also compared the protein levels between the L. monocytogenes parent strain and the ΔBCHL strain (which does not express any alternative σ factors). This analysis identified (i) 33 proteins that showed significantly higher levels (FC ≥ 1.5; p c < 0.05) in the parent strain as compared to the ΔBCHL strain (Additional

file 1: Table S1) and (ii) 44 proteins that show lower levels in the parent as compared to the ΔBCHL mutant (Additional file 1: Table S1). Approximately 40% of the proteins that showed differential production (either up or down) are involved in energy metabolism and transport and binding functions (Figure 1). Among the 33 proteins that showed higher levels in the parent strain, (i) two were also found to be positively regulated by σH; (ii) one was also positively regulated ID-8 by σH and σL, and (iii) one was also positively regulated by σH, σL and σC (Figure 2; Table 4). In addition, 12 of the 29 proteins that were found to be positively regulated in the parent strain, were also found to be positively regulated by σB in a recent proteomics study, which compared L. monocytogenes parent strain 10403S and ΔsigB mutant grown to stationary phase under the same conditions as used here [23]. While these 12 proteins likely represent proteins that are positively regulated by σB, the other 17 proteins that showed higher levels in the parent strain as compared to the ΔBCHL strain, but were not identified as positively regulated by any of the alternative σ factors, represent candidate proteins for redundant co-regulation by multiple alternative σ factors. Future experiments using an L.