EFFECTS OF REDUCED OXYGEN TENSION ON GROWTH RESPONSES OF METHIONINE AND VITAMIN B 12 STIMULATED MUTANTS OF COLIFORM BACTERIA

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Abstract
Twenty-seven mutants of coliform bacteria, each having a genetic block in methionine metabolism, were studied. Methionine, methionine sulfoxide, acetylmethionine, and methionine peptides support growth of these mutants in the presence of O2 but, in contrast to the other compounds, methionine is inactive in the absence of O2. Nutritional experiments did not identify the defect in anaerobic methionine metabolism. Precursors such as homocysteine or homocystine were utilized for growth without regard to O2 and vitamin B12-stimulated mutants showed no O2 dependence for growth with the vitamin. Permeability was discounted, but not eliminated, as a factor since one Aerobacter mutant demonstrated O2-dependent growth for both methionine and s-adenosyl-L-methionine. Methionine sulfoxide was shown to have greater activity than methionine in antagonizing sulfanilamide inhibition in Escherichia coli B. Vitamin B12 did not affect sulfanilamide inhibition in the wild strain B, but did stimulate growth of a vitamin B12-mutant of the B strain in the presence of sulfanilamide. Methionine sulfoxide, but not methionine, stimulated growth of the B12 mutant in the presence of sulfanilamide both aerobically and anaerobically.