The Bacillus subtilis σM regulon and its contribution to cell envelope stress responses


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The Bacillus subtilis extracytoplasmic function (ECF) σM 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 σM. In many cases, expression is only partially dependent on σM because of both overlapping promoter recognition with other ECF σ factors and the presence of additional promoter elements. Genes regulated by σM have a characteristic pattern of induction in response to cell envelope-acting antibiotics as evidenced by hierarchical clustering analysis. σM 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 σW, σB and several two-component regulatory systems (e.g. LiaRS, YycFG, BceRS). Activation of the σM regulon increases expression of proteins functioning in transcriptional control, cell wall synthesis and shape determination, cell division, DNA damage monitoring, recombinational repair and detoxification.