Are physiological oxygen concentrations mutagenic

HYPERBARIC oxygen is known to be mutagenic towards Escherichia coli1–3. But, can oxygen be mutagenic at tensions physiological to man? We have studied this question using oxygen-sensitive mutants of the histidine auxotroph strain TA100 of Salmonella typhimurium constructed by Ames and his coworkers as part of a test system for carcinogens4. We find that oxygen tensions physiological to higher animals are mutagenic towards these organisms.