The Influence of Nitrate and Nitrite on the Competition between Dissimilatory Nitrite Reduction to Ammonium and Denitrification

Dissimilatory reduction of nitrite to ammonium (DNRA) and denitrification are two biological processes that occur in natural and man-made ecosystems, where nitrate and nitrite are the terminal electron acceptors. The understanding of the environmental factors that determine which of these processes dominate, can contribute to optimising engineered nitrogen conversion processes. In the present study, we aimed to quantitatively assess the influence of nitrite as electron acceptor compared to nitrate on the competition between denitrification and DNRA. A nitrogen limited continuous mixed culture was used, with acetate as carbon source and electron donor, and nitrate and/or nitrite as electron acceptor. It is shown that replacing nitrate by nitrite does not change the conversions nor the microbial community structure in the system. DNRA initially was, and remained the dominant process and the microbial community consisted in all experiments for more than 90% of Geobacter sp. It remains unclear if the denitrification activity observed can be fully attributed to the side population Betaproteobacteria, or that denitrification was also (partly) catalysed by Geobacter sp. The Ks, qsmax and Yxs values obtained in this study can be used in environmental modelling studies and in the bioprocess engineering of nitrate and nitrite containing streams.