The Bacillus subtilis Extracytoplasmic-Function σ X Factor Regulates Modification of the Cell Envelope and Resistance to Cationic Antimicrobial Peptides

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Abstract
Bacillus subtilis contains seven extracytoplasmic-function σ factors that activate partially overlapping regulons. We here identify four additional members of the σ X regulon, pbpX (penicillin-binding protein), ywnJ , the dlt operon ( d -alanylation of teichoic acids), and the pss ybfM psd operon (phosphatidylethanolamine biosynthesis). Modification of teichoic acids by esterification with d -alanine and incorporation of phosphatidylethanolamine into the cell membrane have a common consequence: in both cases positively charged amino groups are introduced into the cell envelope. The resulting reduction in the net negative charge of the cell envelope has been previously implicated as a resistance mechanism specific for cationic antimicrobial peptides. Consistent with this notion, we find that both sigX and dltA mutants are more sensitive to nisin than wild-type cells. We conclude that activation of the σ X regulon serves to alter cell surface properties to provide protection against antimicrobial peptides.
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