Nitrogen Fixation by Extracts of Mycobacterium flavum 301

Crude extracts of lactate‐grown Mycobacterium flavum 301 reduced acetylene to ethylene with NADH as electron donor provided benzyl viologen was present; ATP was required. Lactate, pyruvate, H 2 or glucose‐6‐phosphate were also active donors via appropriate dehydrogenases. Crude extracts also reduced cyanide to methane with NADH, ATP and benzyl viologen. Debris (composed of wall and membrane fragments) had lactic, pyruvic and NADH dehydrogenase activities. They reduced acetylene with sodium dithionite or NADH. Benzyl viologen was not required with NADH; ATP and O 2 inhibited the reaction. Crude extracts were as sensitive to inactivation by oxygen as extracts from anaerobic bacteria. Glutathione decreased and ATP increased oxygen‐sensitivity. Debris preparations were not inactivated by oxygen. These results suggest that the nitrogen‐fixing system of M. flavum 301 resembles those of other aerobes, but that its mechanisms for protecting nitrogenase from oxygen are more primitive.