Competition between Free and Combined Nitrogen in Nutrition of Azotobacter

Abstract
A. vinelandii was grown in media containing sources of fixed N in presence of atmosphere with the stable isotope N15. After 15 to 40 hrs. the N15 content of the washed cells was detd. spec-trometrically. Only NH4+ and compounds readily converted into NH4+ inhibit fixation. This suggests but does not prove that ammonia may be a primary product in N fixation. Nitrates inhibit fixation after a period of "adaptation" during which the organism may develop an enzyme to convert nitrate to NH4+.

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