Substrate diversity of an active heterotrophic nitrifier, an Alcaligenes sp.

Abstract

Several oximes, acetohydroxamic acid, and 3-nitropropionic acid were examined to determine if they could serve as substrates for heterotrophic nitrification by an Alcaligenes sp., previously isolated from soil and shown to actively nitrify pyruvic oxime. Neither acetohydroxamic acid, the aldoximes of acetaldehyde or butyraldehyde, or the alkyl oxime, acetone oxime, were used as nitrification substrates or as sole sources of carbon or nitrogen. α-Ketobutyric oxime, α-ketoglutaric oxime, and 3-nitropropionic acid, however, were nitrified and growth occurred when these compounds served as sole sources of carbon and nitrogen. Experiments with resting cells and cell-free extracts of the Alcaligenes sp. grown on α-ketobutyric oxime and α-ketoglutaric oxime indicate that these substrates are nitrified via an organic pathway as the rates of hydroxylamine (the nitrogen hydrolysis product) conversion are kinetically insufficient. 3-Nitropropionic acid metabolism by resting cells of the Alcaligenes sp. grown in 3-nitropropionic medium is restricted to nitrite production. The substrate specificities of the Alcaligenes sp. for heterotrophic nitrification and the relevance of the mineralization of 3-nitropropionic acid by the bacterium are discussed.