Lethal and mutagenic effects of irradiated medium on Escherichia coli

Abstract

X- and γ-irradiated synthetic minimal medium was found to have a strong lethal effect on E. coli incubated in it. The lethal effect of γ-irradiated medium increased when the dose to the medium was increased from 50 to 500 krad. The production of cytotoxic principle was found to be dose-rate dependent, and its effect was inversely related to the number of bacteria per ml seeded into the irradiated medium. The lethal effect was found to arise from irradiation of the glucose component of the medium. The observations that the lethal effect of irradiated medium could be duplicated by adding amounts of hydrogen peroxides that will be obtained in the medium by irradiation and that catalase completely negated the effect of irradiated medium suggest that peroxides constitute the cytotoxic principle. Treatment with irradiated medium was found to enhance significantly the mutation rates for both forward and reverse mutations.