Nitrate reduction to ammonia: a dissimilatory process in Enterobacter amnigenus

Abstract

Thirty-four bacterial isolates from an agricultural soil anaerobically preincubated in the presence of glucose were tested for their ability to reduce nitrate to ammonia or to denitrify in two different media: nitrate broth and a minimal medium enriched with glucose. Ten isolates were considered denitrifying bacteria and 7 were dissimilatory ammonia producers. Ammonia production by the isolate identified as Enterobacter amnigenus was quantified and attained 50% of 138 mg∙L−1 of added NO3− N. The dissimilatory character of this reduction was clearly confirmed by culturing this 15N-labeled bacterium in the presence of unlabeled nitrite. Nitrous oxide was produced at the same time as nitrite was reduced to ammonia. Increasing nitrate N levels from 48 to 553 mg∙L−1 in culture medium resulted in an increase in the level of nitrite produced and simultaneously a decrease in ammonia and nitrous oxide production. Key words: dissimilatory nitrate reduction, dissimilatory ammonia production, denitrification, Enterobacter amnigenus, 15N.