A psychrotrophic heterotrophic nitrifying-aerobic denitrifying bacterium was newly isolated and identified as Acinetobacter sp. with phenotypic and phylogenetic analysis. The strain possessed excellent tolerance to low temperature with 20 degrees C as its optimum and 4 degrees C as viable. Moreover, ammonium, nitrite and nitrate could be removed efficiently under low-temperature, solely aerobic conditions with little accumulation of intermediates. The average removal rate at 10 degrees C reached as high as 3.03, 2.51 and 1.88 mg N L-1 h(-1) for ammonium, nitrite and nitrate respectively. N-2 was produced through heterotrophic nitrification and aerobic denitrification via nitrite but N2O was never detected in the whole process. Nitrogen balance analysis indicated that N-2 and intracellular nitrogen were two major fates of the initial ammonium, accounting for 32.4 and 49.2%, respectively. Further aerated batch test demonstrated efficient removal of COD and TN from synthetic wastewater, which implied promising practical application of the present strain. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.