Mutations in Multidrug Efflux Homologs, Sugar Isomerases, and Antimicrobial Biosynthesis Genes Differentially Elevate Activity of the ς X and ς W Factors in Bacillus subtilis

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Abstract
The ς X and ς W extracytoplasmic function sigma factors regulate more than 40 genes in Bacillus subtilis . ς W activates genes which function in detoxification and the production of antimicrobial compounds, while ς X activates functions that modify the cell envelope. Transposon mutagenesis was used to identify loci which negatively regulate ς W or ς 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 ς 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.

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