THE DELTA(ARGF-LACZ)205(U169) DELETION GREATLY ENHANCES RESISTANCE TOHYDROGEN-PEROXIDE IN STATIONARY-PHASE ESCHERICHIA-COLI

In this study, we demonstrate that a strain bearing the Delta(argF-lac Z)205(U169) deletion exhibits a high level of resistance to hydrogen p eroxide compared with its undeleted parent. Our initial investigation of the mechanism behind the observed differences in peroxide resistanc e when parent and mutant strains are compared indicates that the paren t strain carries a region near argF that is responsible for the H2O2-s ensitive phenotype, which we have named katC. The H2O2 resistance phen otype of the Delta katC [Delta(argF-lacZ)205(U169)] mutant strain can be duplicated by Tn9 insertion in a specific locus (katC5::Tn9) which maps near argF. The increased H2O2 resistance of the Delta katC and ka tC5::Tn9 mutant strains can be seen only when cells are grown to stati onary phase; exponential-phase cells are unaffected by the presence or absence of katC. This H2O2 resistance mechanism requires functional k atE and katF genes, which suggests that the mechanism of H2O2 resistan ce may involve the activity of the stationary-phase-specific catalase HPII. Cloning, DNA sequencing, and analysis of the katC5::Tn9 insertio n allele in comparison with its parent allele implicate two insertion elements, IS1B and IS30B, and suggest that their presence sensitizes p arent cells to H2O2.