AD-1, an aerobic denitrifier, was isolated from activated sludge and identified as Pseudomonas stutzeri. AD-1 completely removed NO3- or NO2- and removed 99.5% of NH4+ during individual culturing in a broth medium with an initial nitrogen concentration of approximately 50 mg L. Results showed that larger amounts of nitrogen were removed through assimilation by the bacteria. And when NH4+ was used as the sole nitrogen source in the culture medium, neither NOi nor NOT was detected, thus indicating that AD-1 may not be a heterotrophic nitrifier. Only trace amount of N20 was detected during the denitrification process. Single factor experiments indicated that the optimal culture conditions for AD-1 were: a carbon-nitrogen ratio (C/N) of 15, a temperature of 25 degrees C and sodium succinate or glucose as a carbon source. In conclusion, due to the ability of AD-1 to utilize nitrogen of different forms with high efficiencies for its growth while producing only trace emissions of N20, the bacterium had outstanding potential to use in the bioremediation of high-nitrogen-containing wastewaters. Meanwhile, it may also be a proper candidate for biotreatment of high concentration organic wastewater. (C) 2018, The Society for Biotechnology, Japan. All rights reserved.