N2O production from hydroxylamine oxidation and corresponding hydroxylamine oxidoreductase involved in a heterotrophic nitrifier A. faecalis strain NR

N2O production from NH2OH oxidation involved in a heterotrophic nitrifier Alcaligenes faecalis strain NR was studied. N-15-labeling experiments showed that biological NH2OH consumption by strain NR played a dominant role in N2O production, although chemical reaction between NH2OH and O-2 indeed existed. Hydroxylamine oxidoreductase (HAO) from strain NR was partially purified by (NH4)(2)SO4 fractionation and DEAE Cartridge chromatography. The maximum activity of HAO was 9.60 mU with a specific activity of 92.04 mU/(mg protein) when K3Fe(CN)(6) was used as an electron acceptor. The addition of Ca2+ promoted the HAO activity, while the presence of Mn2+ inhibited the enzyme activity. The optimal temperature and pH for HAO activity were 30 degrees C and 8. Analysis of enzyme-catalyzed products demonstrated that NH2OH oxidation catalyzed by HAO from strain NR played significant role in the production of N2O.