Factors relating to the aerotolerance of Spirillum volutans

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Abstract
A variant of the microaerophile Spirillum volutans capable of growth under an air atmosphere (21% oxygen) was obtained by sequential selection and stabilization of colonies able to grow on a casein hydrolysate – succinate – potassium metabisulfite medium under an atmosphere of 14, 16, 18, 20, and finally 21% O2. A small amount of bisulfite (0.0025%) was still required, however, for aerobic growth. Both the variant and the wild type lacked catalase activity, and they had the same levels of superoxide dismutase activity. However, the mutant possessed 13 times more donor: hydrogen-peroxide oxidoreductase (peroxidase) activity (0.008 IU) than the wild type (0.0006 IU). An aerotolerant mutant was also isolated in one step by treatment with the mutagenic agent ethyl methane sulfonate, followed by incubation under 21% O2; it was found to possess approximately three times the peroxidase activity of the wild type. This mutant lacked catalase activity and the level of superoxide dismutase activity it contained was comparable with the wild type.