NH(2)OH Disproportionation Mediated by Anaerobic Ammonium-oxidizing (Anammox) Bacteria

Anammox bacteria produce N(2) gas by oxidizing NH(4)(+) with NO(2)(–), and hydroxylamine (NH(2)OH) is a potential intermediate of the anammox process. N(2) gas production occurs when anammox bacteria are incubated with NH(2)OH only, indicating their capacity for NH(2)OH disproportionation with NH(2)OH serving as both the electron donor and acceptor. Limited information is currently available on NH(2)OH disproportionation by anammox bacteria; therefore, the stoichiometry of anammox bacterial NH(2)OH disproportionation was examined in the present study using (15)N-tracing techniques. The anammox bacteria, Brocadia sinica, Jettenia caeni, and Scalindua sp. were incubated with the addition of (15)NH(2)OH, and the production of (15)N-labeled nitrogenous compounds was assessed. The anammox bacteria tested performed NH(2)OH disproportionation and produced (15-15)N(2) gas and NH(4)(+) as reaction products. The addition of acetylene, an inhibitor of the anammox process, reduced the activity of NH(2)OH disproportionation, but not completely. The growth of B. sinica by NH(2)OH disproportionation (–240.3‍ ‍kJ mol NH(2)OH(–1) under standard conditions) was also tested in 3 up-flow column anammox reactors fed with 1) 0.7‍ ‍mM NH(2)OH only, 2) 0.7‍ ‍mM NH(2)OH and 0.5‍ ‍mM NH(4)(+), and 3) 0.7‍ ‍mM NH(2)OH and 0.5‍ ‍mM NO(2)(–). NH(2)OH consumption activities were markedly reduced after 7‍ ‍d of operation, indicating that B. sinica was unable to maintain its activity or biomass by NH(2)OH disproportionation.