The characteristics of a novel heterotrophic nitrification–aerobic denitrification bacterium, Bacillus methylotrophicus strain L7

Bacillus methylotrophicus strain L7, exhibited efficient heterotrophic nitrification–aerobic denitrification ability, with maximum NH 4 + -N and NO 2 - -N removal rate of 51.58 mg/L/d and 5.81 mg/L/d, respectively. Strain L7 showed different gaseous emitting patterns from those strains ever described. When 15NH4Cl, or Na15NO2, or K15NO3 was used, results of GC–MS indicated that N2O was emitted as the intermediate of heterotrophic nitrification or aerobic denitrification, while GC–IRMS results showed that N2 was produced as end product when nitrite was used. Single factor experiments suggested that the optimal conditions for heterotrophic nitrification were sodium succinate as carbon source, C/N 6, pH 7–8, 0 g/L NaCl, 37 °C and a wide range of NH 4 + -N from 80 to 1000 mg/L. Orthogonal tests showed that the optimal conditions for aerobic denitrification were C/N 20, pH 7–8, 10 g/L NaCl and DO 4.82 mg/L (shaking speed 50 r/min) when nitrite was served as substrate.