Anaerobic Ammonia Oxidation in the Presence of Nitrogen Oxides (NO(x)) by Two Different Lithotrophs

The anaerobic ammonia-oxidizing activity of the planctomycete Candidatus “Brocadia anammoxidans” was not inhibited by NO concentrations up to 600 ppm and NO(2) concentrations up to 100 ppm. B. anammoxidans was able to convert (detoxify) NO, which might explain the high NO tolerance of this organism. In the presence of NO(2), the specific ammonia oxidation activity of B. anammoxidans increased, and Nitrosomonas-like microorganisms recovered an NO(2)-dependent anaerobic ammonia oxidation activity. Addition of NO(2) to a mixed population of B. anammoxidans and Nitrosomonas induced simultaneous specific anaerobic ammonia oxidation activities of up to 5.5 mmol of NH(4)(+) g of protein(−1) h(−1) by B. anammoxidans and up to 1.5 mmol of NH(4)(+) g of protein(−1) h(−1) by Nitrosomonas. The stoichiometry of the converted N compounds (NO(2)(−)/NH(3) ratio) and the microbial community structure were strongly influenced by NO(2). The combined activity of B. anammoxidans and Nitrosomonas-like ammonia oxidizers might be of relevance in natural environments and for technical applications.