Simultaneous nitrification and denitrification conducted by Halomonas venusta MA-ZP17-13 under low temperature conditions

Nitrification is a key step in the global nitrogen cycle. Compared with autotrophic nitrification, heterotrophic nitrification remains poorly understood. In this study, Halomonas venusta MA-ZP17-13, isolated from seawater in shrimp aquaculture ( Penaeus vannamei ), could simultaneously undertake nitrification and denitrification. With the initial ammonium concentration at 100 mg/L, the maximum ammonium-nitrogen removal rate reached 98.7% under the optimal conditions including C/N concentration ratio at 5.95, pH at 8.93, and NaCl at 2.33%. The corresponding average removal rate was 1.37 mg/(L·h) (according to nitrogen) in 3 d at 11.2°C. By whole genome sequencing and analysis, nitrification- and denitrification-related genes were identified, including ammonia monooxygenase, nitrate reductase, nitrite reductase, nitric oxide dioxygenase and nitric oxide synthase; while no gene encoding hydroxylamine oxidase was identified, it implied the existence of a novel nitrification pathway from hydroxylamine to nitrate. These results indicate heterotrophic bacterium H. venusta MA-ZP17-13 can undertake simultaneous nitrification and denitrification at low temperature and has potential for NH 4 + -N/NH 3 -N removal in marine aquaculture systems.