[Identification and denitrification of an aerobic bacterium]

Denitrifying bacteria play an important role in the biological nitrogen removal process, especially the aerobic denitrifying bacteria. However, there are few studies on aerobic denitrifying bacteria. The present study aimed at the isolation of aerobic denitrifying bacteria with high ammonium and nitrite nitrogen removing ability from environmental samples, and its phylogeny and denitrifying characteristics.

Based on the aerobic denitrifying activity, ammonium and nitrite nitrogen removing ability, the strains were isolated from sludge, water and sediment in a eutrophicated pond. A strain with the highest activities was identified according to its morphological, physiological and biochemical properties and phylogenetic analysis of its 16S rRNA sequence. By using NO(3-)-N, NH(4+)-N and NO(2-)-N as the sole nitrogen source respectively, its denitrifying characteristics, and the effects of culture conditions such as initial pH of medium, temperature, carbon source, shaking speed on the ability of removing ammonium and nitrite nitrogen, were investigated under aerobic condition.

Among the isolated strains, strain C-4 showed the highest ability of removing ammonium and nitrite nitrogen. Strain C-4 was identified as Acinetobacter sp.. Under the conditions of sodium citrate as carbon source, temperature 30 degres C, shaking speed 120 r/min, cell age of 18 h, pH 8.5 for 200 mg/L NH(4+)-N medium and pH 7.5 for 100 mg/L NO(2-)-N medium, the net removal efficiency of nitrogen were 65.8% and 47.8% after 15 h and 12 h, respectively.

An aerobic denitrifying strain Acinetobacter sp. C-4 (HQ896038) was isolated from water pond, and it exhibited high net removal efficiency of nitrogen in relative media. The net removal efficiency of nitrogen of strain C-4 was 73.04% in dealing with a eutrophicated pond water.