A hydrogen peroxide resistant mutant of Spirillum volutans has NADH peroxidase activity but no increased oxygen tolerance

The catalase-negative microaerophile Spirillum volutans is killed rapidly by levels of H2O2 greater than 10 mu M. A mutant isolated by single step mutagenesis with diethyl sulfate was able to survive and grow after exposure to 40 mu M H2O2 and was effective in eliminating H2O2 added to the medium. Nevertheless, the mutant was no more tolerant to O-2 than the wild type. The only apparent phenotypic difference between the wild type and the mutant was that the mutant had high NADH peroxidase activity (0.072 IU.mg(-1)) whereas the wild type had no detectable activity (<0.0002 IU.mg(-1)). NADH peroxidase has not previously been reported in gram-negative bacteria or in bacteria having a strictly respiratory type of metabolism.