MUTATION OF THE BACILLUS-SUBTILIS ALKYL HYDROPEROXIDE REDUCTASE (AHPCF) OPERON REVEALS COMPENSATORY INTERACTIONS AMONG HYDROGEN-PEROXIDE STRESS GENES

In Bacillus subtilis, hydrogen peroxide induces the synthesis of catal ase (KatA), alkyl hydroperoxide reductase (AhpCF), and a DNA-binding p rotein of the Dps family (MrgA). KatA, AhpCF, heme biosynthesis enzyme s, and MrgA are also induced upon entry into stationary phase under co nditions of iron and manganese limitation, In an effort to define the peroxide regulon repressor, PerR, we used mini-Tn10 mutagenesis to ide ntify loci affecting the regulation of mrgA. From this screen, we isol ated two mini-Tn10 insertions in ahpC, the gene encoding the small sub unit of AhpCF, that increase the transcription of mrgA-lacZ even in ir on-supplemented minimal medium, Indeed, these ahpC::Tn10 insertions le ad to elevated expression from all peroxide regulon promoters, includi ng those for mrgA, katA, hemAXCDBL, and ahpCF. As a result, the ahpC:: Tn10 mutants display an increased resistance to H2O2. The ahpCF promot er region contains three sequences similar to the peroxide regulon con sensus operator (per box), We demonstrate that the ability of ahpC::Tn 10 mutations to derepress mrgA requires aerobic growth. In contrast, a second distinct trans-acting regulatory mutation bypasses this requir ement for aerobic growth, Since the peroxide regulon is activated in t he absence of AhpCF, which degrades alkyl hydroperoxides, we propose t hat organic hydroperoxides may be physiologically relevant inducers in vivo.