Nitrite oxidation by heterotrophic bacteria under various nutritional and aerobic conditions

The nitrite transforming activities of heterotrophic bacteria from culture collections and isolates from activated sludge were studied under various nutritional and aerobic conditions. Among the 48 organisms tested, 17 strains, many of which are reported as denitrification negatives, consumed 1-5 mM of nitrite and accumulated corresponding amounts of nitrate. Twelve strains, many of which are denitrification-positive, consumed nitrite with the accumulation of less nitrate, while more than 1 mM nitrite was consumed but little nitrate was accumulated by 14 strains, many of which are Enterobacteriaceae or lactic acid bacteria. None of the organisms formed significant nitrate in the medium without nitrite, though a considerable amount of ammonia was also accumulated by most strains. Although the growth and nitrate accumulation of Bacillus badius I-73 was affected by the concentrations of sodium nitrite and peptone and by the culture volume, the amount of nitrate accumulated was always proportional to that of the nitrite consumed. Intact cells of B. badius I-73 produced almost the same amount of nitrate as the decrease in nitrite. On the other hand, in B. subtilis I-41, a denitrification-positive isolate, the ratio of the amount of nitrate accumulated to that of nitrite consumed varied from 0-100% depending on the culture conditions.