The bacterium isolated from sea sludge Paracoccus versutus LYM was characterized with the ability of aerobic denitrification. Strain LYM performs perfect activity in aerobically converting over 95% NO3--N (approximate 400 mg L-1) to gaseous products via nitrite with maximum reduction rate 33 mg NO3--N L-1 h(-1). Besides characteristic of aerobic denitrification, strain LYM was confirmed in terms of the ability to be heterotrophic nitrification and aerobic denitrification (HNAD) with few accumulations of intermediates. After the nitrogen balance and enzyme assays, the putative nitrogen pathway of HNAD could be NH4+ -> NH2OH -> NO2- -> NO3- then NO3- was denitrified to gaseous products via nitrite. N-2 was sole denitrification product without any detection of N2O by gas chromatography. Strain LYM could also simultaneously remove ammonium and additional nitrate. Meanwhile, the accumulated nitrite had inhibitory effect on ammonium reduction rate. (C) 2013 Elsevier Ltd. All rights reserved.