Functional analysis of SigH in Bacillus cereus ATCC14579 and regulon prediction in the B. cereus group

Bacillus cereus is a common pathogen causing frequent foodborne outbreaks with diarrheal or emetic syndromes. Its endospores survive mild processing conditions, leading to food spoilage and intoxication. Here, we assess the role of B. cereus ATCC14579 SigH (Spo0H), an alternative transition-phase associated RNA polymerase sigma factor. Comparative phenotypic analysis of a B. cereus ATCC14579 sigH-deletion mutant (ΔsigH) revealed differences in a wide range of phenotypes. First and foremost, ΔsigH lost its sporulation ability. Phenotypic microarray and growth analysis showed a dramatic loss of the ability to utilize over 200 di- and tri-peptides for biomass generation. Furthermore, stationary phase survival under non-sporulating conditions (BHI) was severely compromised, showing a 3-log reduction after 3 days. ΔsigH also exhibited altered swimming and swarming behavior, including an impaired chemotactic response to several amino acids, and a severe reduction in liquid-air interphase biofilm formation. To interlink genotype and phenotype, we combined comparative transcriptomics, 5'RACE and in silico analysis to define the SigH promoter consensus and extract its regulon. Comparative genomics across the B. cereus group revealed a highly conserved core regulon with additional strain-specific features. The involvement of SigH in newly described phenotypes and controlling large numbers of transcriptional regulators and chaperones, points to crucial roles of SigH in transition phase performance and governing both bacterial differentiation and metabolic adaptation in B. cereus.