Identification of the σB Regulon of Bacillus cereus and Conservation of σB-Regulated Genes in Low-GC-Content Gram-Positive Bacteria

摘要

The alternative sigma factor σB has an important role in the acquisition of stress resistance in many gram-positive bacteria, including the food-borne pathogen Bacillus cereus. Here, we describe the identification of the set of σB-regulated genes in B. cereus by DNA microarray analysis of the transcriptome upon a mild heat shock. Twenty-four genes could be identified as being σB dependent as witnessed by (i) significantly lower expression levels of these genes in mutants with a deletion of sigB and rsbY (which encode the alternative sigma factor σB and a crucial positive regulator of σB activity, respectively) than in the parental strain B. cereus ATCC 14579 and (ii) increased expression of these genes upon a heat shock. Newly identified σB-dependent genes in B. cereus include a histidine kinase and two genes that have predicted functions in spore germination. This study shows that the σB regulon of B. cereus is considerably smaller than that of other gram-positive bacteria. This appears to be in line with phylogenetic analyses where σB of the B. cereus group was placed close to the ancestral form of σB in gram-positive bacteria. The data described in this study and previous studies in which the complete σB regulon of the gram-positive bacteria Bacillus subtilis, Listeria monocytogenes, and Staphylococcus aureus were determined enabled a comparison of the sets of σB-regulated genes in the different gram-positive bacteria. This showed that only three genes (rsbV, rsbW, and sigB) are conserved in their σB dependency in all four bacteria, suggesting that the σB regulon of the different gram-positive bacteria has evolved to perform niche-specific functions.