Escherichia coli cell inactivation by superoxide anion and hydrogen peroxide.

Abstract

The effect of superoxide anion (O2-) on killing of cells was studied. E. coli was killed by a non-enzymatical O2--generating system, i.e. a phenazine methosulfate (PMS)-NADH system. Both polA and recA repair-deficient mutants were more sensitive to O2- than wild type cells. Furthermore, using the polA mutant strain, it was clearly shown that incubation in growing medium increased survival, indicating the involvement of a rec-dependent repair system. It was concluded that the direct cause of cell death induced by O2- was DNA damage. When a scavenger of the active oxygen, such as superoxide dismutase (SOD) or catalase, was present in the reaction buffer during O2- treatment, the survival of cells increased. Of especial note, cells were completely protected by addition of catalase. It was suggested that H2O2 produced from O2- and H2O was a molecule more toxic to E. coli cells than the O2- itself in this system. When SOD and catalase were induced inside cells by adding methyl-viologen in the medium, a protective effect against O2- appeared. Cells treated with methyl-viologen were also resistant, although slightly, to aerobic γ-ray irradiation, suggesting that the scavenger of active oxygen in cells was partly responsible for protection against γ-ray irradiation. It is deduced that O2- and/or H2O2 generated in cells may be one of the causes of cell damage by aerobic γ-ray irradiation.