Mutations in multidrug efflux homologs, sugar isomerases, and antimicrobial biosynthesis genes differentially elevate activity of the sigma(X) and sigma(W) factors in Bacillus subtilis

The sigma(X) and sigma(W) extracytoplasmic function sigma factors regulate more than 40 genes in Bacillus subtilis. sigma(W) activates genes which function in detoxification and the production of antimicrobial compounds, while sigma(X) activates functions that modify the cell envelope. Transposon mutagenesis was used to identify loci which negatively regulate sigma(W) or sigma(X) as judged by up-regulation from the autoregulatory promoter site P(W) or P(X). Fourteen insertions that activate P(W) were identified. The largest class of insertions are likely to affect transport. These include insertions in genes encoding two multidrug efflux protein homologs (yqgE and yulE), a component of the oligopeptide uptake system (oppA), and two transmembrane proteins with weak similarity to transporters (yhdP and yueF). Expression from P(W) is also elevated as a result of inactivation of at least one member of the sigma(W) regulon (ysdB), an ArsR homolog (yvbA), a predicted rhamnose isomerase (yulE), and a gene (pksR) implicated in synthesis of difficidin, a polyketide antibiotic. In a parallel screen, we identified seven insertions that up-regulate P(X). Remarkably, these insertions were in functionally similar genes, including a multidrug efflux homolog (yitG), a mannose-6-phosphate isomerase gene (yjdE), and loci involved in antibiotic synthesis (srfAB and possibly yogA and yngK). Significantly, most insertions that activate P(W) have little or no effect on P(X), and conversely, insertions that activate P(X) have no effect on P(W). This suggests that these two regulons respond to distinct sets of molecular signals which may include toxic molecules which are exported, cell density signals, and antimicrobial compounds.