Abstract
A heterotrophic nitrifying Alcaligenes sp., previously isolated from soil and shown to be very active in the aerobic oxidation of pyruvic oxime (and hydroxylamine) to nitrite, is now shown to be quite active as a dentrifier. The bacterium synthesized nitrite, nitrous oxide, and nitrogen gas from nitrate when grown anaerobically and could individually reduce nitrate, nitrite, nitric oxide, and nitrous oxide to nitrogen gas when the nitrogen-oxides were added to dense cell suspensions. No evidence was obtained for the release of nitric oxide during reduction of nitrate and nitrite. The specific rates of reduction of the nitrogen-oxides were similar to those of well-known laboratory strains of denitrifying bacteria. The induction of an entire set of denitrifying enzymes at normal levels in a heterotrophic nitrifier is novel.