Acinetobacter junii YB was found to exhibit efficient heterotrophic nitrification and aerobic denitrification ability, with the maximum ammonium, nitrite and nitrate removal rate of 8.82, 8.45 and 7.98 mg/L/h, respectively. Meanwhile, ammonium was found to be removed preferentially in the process of simultaneous nitrification and denitrification in mixed N-sources. The successful PCR amplification of hao, napA and nirS genes further provided additional evidence of heterotrophic nitrification and aerobic denitrification by strain YB. In addition, orthogonal test showed that dissolved oxygen was the most important determinant of nitrite removal, and the optimal conditions were C/N 15, pH 7.0, 37 degrees C and 200 rpm. Furthermore, stable nitrogen and organics removal were achieved by one-time dosing of enriched bacteria in a sequencing batch reactor. The inoculation of strain YB significantly improved the denitrification efficiency with minimal accumulation of nitrified products, which demonstrated high potential of the isolate for future practical applications. (C) 2015 Elsevier Ltd. All rights reserved.