At least three experiments were performed, and results from a representative experiment performed in

triplicates are shown. Error bars indicate standard deviation and sometimes fall within the data label. We assayed the resistance of the ΔarcA mutant E. coli to hydrogen peroxide (H2O2). Overnight culture of the ΔarcA mutant E. find more coli was exposed to H2O2, and its survival was compared to that of the wild type E. coli. The ΔarcA mutant E. coli was more susceptible than the wild type E. coli (Figure 1A). Plasmid pRB3-arcA, which carries a wild type allele of arcA in plasmid pRB3-273C [38, 40], complemented the survival defects in H2O2. This indicates that the susceptible phenotype of the ΔarcA CRT0066101 concentration mutant E. coli was likely due to the deletion of the arcA allele (Figure 1A). Assays

performed with log-phase culture of the ΔarcA mutant E. coli yielded similar results (data not shown). Similar results were obtained with LB broth and M9 minimal medium, results obtained with LB broth are shown (Figure 1). The same analysis was carried out for ArcB, the cognate sensor-kinase of the ArcAB system. The ΔarcB mutant E. coli survived less than the wild type parental strain (Figure 1C). We had attempted to clone a wild type allele of arcB into plasmid pRB3-273C to complement the ΔarcB mutant E. coli. However, the cloning efficiency was unusually low as compared to similar cloning attempts we had conducted with the plasmid vector. Of a total of 7 recombinant plasmids we eventually obtained from several transformations, 5 contained mutations at the start codon of arcB and the remaining 2 had mutations that produced truncations early in the ORF (data not shown). This indicates that an over-expression of arcB from a plasmid is probably toxic to E. coli. As an alternative, we constructed a revertant of Resveratrol the ΔarcB mutant E. coli, in which a wild type arcB allele replaced the deleted arcB allele (see Materials and Methods). The revertant mutant of ΔarcB was shown to have the same resistance to H2O2 as the wild type E. coli (Figure 1C). The ArcAB system is dispensable for H2O2 scavenge To determine the mechanism of how the ArcAB system is involved

in H2O2 resistance, we buy BV-6 analyzed the H2O2 scavenging activity of the ΔarcA and ΔarcB mutant of E. coli K12, since a defect in H2O2 scavenging activity may lead to the susceptibility to H2O2. The overnight culture was diluted in LB containing 2 mM of H2O2, and the concentration of the residual H2O2 was measured after various incubation period. The scavenge of H2O2 was measured as the reduction in H2O2 concentration over the incubation period. Our results indicate that both ΔarcA and ΔarcB mutants scavenged H2O2 normally as compared to the wild type E. coli K12., and no deficiency was observed (Figure 2). Figure 2 The ArcAB system is dispensable for H 2 O 2 scavenge. The ΔarcA (square), ΔarcB (triangle) mutant and the wild type E.