In fact, oxygen is toxic to some bacteria. Bacteria are often classified according to their oxygen requirements. Detoxification of superoxides by superoxide dismutase and catalase. Superoxides are first converted to hydrogen peroxide, and then to water. Peroxides are detoxified by catalase or peroxidases.
Obligate aerobes require oxygen to live.
Microaerophiles require oxygen for growth, but they cannot tolerate normal atmospheric levels of oxygen. Too much oxygen seems to interfere with their metabolic enzymes. Obligate anaerobes do not possess superoxide dismutase or catalase, and therefor cannot cope with the toxic by-products of oxygen metabolism. Also, they possess catalase and superoxide dismutase, and so are not affected by the toxic by-products of oxygen. Facultative anaerobes utilize oxygen and aerobic respiration whenever possible.