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

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Abstract
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.