Photobacterium sp. NNA4, an efficient hydroxylamine-transforming heterotrophic nitrifier/aerobic denitrifier.

An efficient heterotrophic nitrifying/aerobic denitrifying strain, Photobacterium sp. NNA4 was isolated from a recirculating aquaculture system (RAS). NNA4 was capable of utilizing ammonia, nitrate or nitrite as sole N-source with maximal removal rates of 12.5 mg/L/h for NHN, 16.4 mg/L/h for NO-N, and 4.5 mg/L/h for NO-N, respectively. Optimal nitrification conditions were: sodium succinate as C-source, 30-37°C, NaCl 1-4%, pH 7.0-8.0, dissolved oxygen 5.89 mg/L, C/N > 10. Gas chromatography/mass spectrometry and gas chromatography/isotope ratio mass spectrometry analyses showed that N and NO were aerobic denitrification products of nitrite and nitrate. NNA4 could tolerate high concentration of hydroxylamine and displayed efficient hydroxylamine-transforming capability. Hydroxylamine oxidoreductase activity using potassium ferricyanide as electron acceptor was 0.042 U. Results revealed that strain NNA4 could oxidize NHOH directly to NO at aerobic conditions. In view of its high removal ability of inorganic nitrogen pollutants and broad salinity tolerance range, NNA4 has great potential in denitrification treatment of types of wastewater with either low salinity (e.g., municipal facilities) or high salinity (e.g., aquaculture, seafood processing).