The Bacillus subtilis σ^M regulon and its contribution to cell envelope stress responses

The Bacillus subtilis extracytoplasmic function (ECF) σ^M factor is activated by cell envelope stress elicited by antibiotics, and by acid, heat, ethanol and superoxide stresses. Here, we have used several complementary approaches to identify genes controlled by σ^M. In many cases, expression is only partially dependent on σ^M because of both overlapping promoter recognition with other ECF σ factors and the presence of additional promoter elements. Genes regulated by σ^M have a characteristic pattern of induction in response to cell envelope-acting antibiotics as evidenced by hierarchical clustering analysis. σ^M also contributes to the expression of the Spx transcription factor and thereby indirectly regulates genes of the Spx regulon. Cell envelope stress responses also include regulons controlled by σ^W, σ^B and several two-component regulatory systems (e.g. LiaRS, YycFG, BceRS). Activation of the σ^M regulon increases expression of proteins functioning in transcriptional control, cell wall synthesis and shape determination, cell division, DNA damage monitoring, recombinational repair and detoxification.