NH₂OH Disproportionation Mediated by Anaerobic Ammonium-oxidizing (Anammox) Bacteria

Abstract

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.

Denitrification in low oxic environments increases the accumulation of nitrogen oxide intermediates and modulates the evolutionary potential of microbial populations

“…For the experiments in oxic batch cultures, we then removed 35 mL of the helium gas and replaced the volume with 35 mL of oxygen gas (purity >99.9%). Finally, we incubated the vials at 30°C with shaking at 150 rpm for 48 h and measured optical densities at 600 nm (OD 600 ) and the concentrations of oxygen, acetate, nitrate, nitrite, nitric oxide, nitrous oxide and nitrogen gas over time as described elsewhere (Oshiki et al, 2022 ). Briefly, we measured OD 600 using an ARVO MX plate reader (Perkin‐Elmer, Waltham, MA, USA); oxygen using a GC‐8A gas chromatograph equipped with a thermal conductivity detector (Shimadzu, Kyōto, Japan); acetate, nitrate and nitrite using a CDD‐6A ion chromatograph (Shimadzu, Kyōto, Japan) equipped with an NI‐424 column (Shodex, Tokyo, Japan) and 15 NO, 15 N 2 O and 15 N 2 using a GCMS‐QP 2010 SE gas chromatograph‐mass spectrometer (Shimadzu, Kyōto, Japan).…”