Pyruvate metabolism by a nitrogen-fixing bacterium.

1. The major products of pyruvate dissimilation by washed intact cells of Achromobacter N4-B under nitrogen-fixing conditions are acetate and formate. The formation of succinate and isocitrate and the assimilated amino acids requires carbon dioxide fixation. 2. The products formed by cells incubated with pyruvate in an atmosphere of nitrogen were compared with those formed by cells incubated in an atmosphere of helium. Production of hydrogen and the formation of succinate were greater under helium than under nitrogen. Production of acetate and formate and the utilization of pyruvate were the same in both atmospheres. 3. Cell-free preparations, unlike intact cells of Achromobacter N4-B, do not evolve hydrogen, but do produce lactate. 4. It is suggested that, in cell-free preparations incapable of fixing nitrogen, electrons are accepted from pyruvate to form lactate rather than being used for the reductive formation of ammonia and hydrogen.