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 catalase (KatA), alkyl hydroperoxide reductase (AhpCF), and a DNA-binding protein of the Dps family (MrgA). KatA, AhpCF, heme biosynthesis enzymes, and MrgA are also induced upon entry into stationary phase under conditions of iron and manganese limitation. In an effort to define the peroxide regulon repressor, PerR, we used mini-Tn10 mutagenesis to identify loci affecting the regulation of mrgA. From this screen, we isolated two mini-Tn10 insertions in ahpC, the gene encoding the small subunit of AhpCF, that increase the transcription of mrgA-lacZ even in iron-supplemented minimal medium. Indeed, these ahpC::Tn10 insertions lead to elevated expression from all peroxide regulon promoters, including those for mrgA, katA, hemAXCDBL, and ahpCF. As a result, the ahpC::Tn10 mutants display an increased resistance to H2O2. The ahpCF promoter region contains three sequences similar to the peroxide regulon consensus operator (per box). We demonstrate that the ability of ahpC::Tn10 mutations to derepress mrgA requires aerobic growth. In contrast, a second distinct trans-acting regulatory mutation bypasses this requirement for aerobic growth. Since the peroxide regulon is activated in the absence of AhpCF, which degrades alkyl hydroperoxides, we propose that organic hydroperoxides may be physiologically relevant inducers in vivo.
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Section of Microbiology, Cornell University, Ithaca, New York 14853, USA.
Chen
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Helmann
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D000332:Aerobiosis; D000595:Amino Acid Sequence; D000693:Anaerobiosis; D029681:Arabidopsis Proteins; D001412:Bacillus subtilis / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D001483:Base Sequence; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D017930:Genes, Reporter; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation; D009876:Operon; D010088:Oxidoreductases / Q000235:genetics*; D010544:Peroxidases; D054464:Peroxiredoxins; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics; D018085:Regulon; D012097:Repressor Proteins / Q000235:genetics; D015534:Trans-Activators
D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C081231:KATA protein, Arabidopsis; C095506:MrgA protein, Bacillus subtilis; D010940:Plant Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D006861:Hydrogen Peroxide; D010088:Oxidoreductases; D010544:Peroxidases; D054464:Peroxiredoxins