Bacillus subtilis MrgA is a Dps(PexB) homologue: evidence for metalloregulation of an oxidative-stress gene

Upon the cessation of exponential growth, Bacillus subtilis enters a transition phase leading to either sporulation or a non-sporulating stationary phase. During this transition period, cells secrete degradative enzymes, become competent for DNA transformation, are motile and acquire resistance to oxidative killing. We now report that mrgA, originally identified as a gene repressed by metal ions, encodes a member of the Dps/PexB family of general stress proteins. Like Escherichia coli Dps(PexB), MrgA forms highly stable, multimeric protein-DNA complexes which accumulate in stationary-phase cells and protect against oxidative killing. MrgA is part of an inducible oxidative stress response in B. subtilis: mrgA is induced by hydrogen peroxide, and a strain lacking MrgA displays increased sensitivity to oxidative killing. In addition, a hydrogen peroxide-resistant mutant, which constitutively overproduces catalase and alkyl hydroperoxide reductase, also overproduces MrgA. These results indicate a complex interplay between metal ions and the expression of the B. subtilis oxidative stress response.