Enzymatic defenses against the toxicity of oxygen and of streptonigrin in Escherichia coli

Abstract

Anaerobically grown E. coli K-12 contain only 1 superoxide dismutase and that is the Fe-containing isozyme found in the periplasmic space. Exposure to O2 caused the induction of a Mn-containing superoxide dismutase and of another, previously undescribed, superoxide dismutase, and of catalase and peroxidase. These inductions differed in their responsiveness towards O2. Thus the very low levels of O2 present in deep, static, aerobic cultures were enough for nearly maximal induction of the Mn-superoxide dismutase. Induction of the new superoxide dismutase, catalase and peroxidase required the much higher levels of O2 achieved in vigorously agitated aerobic cultures. Anaerobically grown cells showed a much greater O2 enhancement of the lethality of streptonigrin than did aerobically grown cells, indicating that streptonigrin can serve as an intracellular source of superoxide. Anaerobically grown cells in which enzyme inductions were prevented by puromycin were damaged by exposure to air. This damage was evidenced both as a decline in viable cell count and as structural abnormalities evident by EM.