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

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