[Identification and characteristics of a marine aerobic denitrifying bacterium]

An aerobic denitrifying bacterium, strain 2-8, was isolated from a biological aerated filter in a recirculating marine aquaculture system, phylogeny and characteristics of the strain was further studied.

Sequence of the 16S rRNA gene was analyzed and the factors affect the denitrifying ability of strain 2-8 were investigated, including carbon source, C/N ratio, initial pH, NaCl concentration, temperature and shaker speed.

Strain 2-8 was identified as Pseudomonas sp. based on the analysis of its 16S rRNA gene sequence which showed highest similarity (99.9%) to Pseudomonas segetis FR1439(T) (AY770691). The results indicated that carbon source and C/N ratio exhibited significant influences on aerobic denitrifying capacity of strain 2-8. Strain 2-8 could grow a little on acetate, succinate and citrate as sole carbon source, and the removal rates of NO3- -N at 140 mg/L were higher than 65% despite of the accumulation of NO2- -N around 35 mg/L. It grew quite well on glucose as sole carbon source, however, the removal rate of nitrate was not so high as on other carbon source. The optimum C/N ratio was 15, as lower C/N ratios may lead to nitrite accumulation. The optimum temperature and pH for its aerobic denitrification were 30 degrees C and 7.5, respectively. Strain 2-8 could grow and exhibit aerobic denitrifying ability at a wide range of NaCl concentrations (0-30 g/L). The highest nitrogen removal appeared under the condition of 160 r/min shaking culture.

When cultured in the conditions of NO3- -N at 140 mg/L, sodium citrate as sole carbon source, C/N ratio at 15, pH 7.5, NaCl at 30 g/L, 30 degrees C and 160 r/min of the shaker, strain 2-8 removed up to 92% of the nitrogen within 48 hours, and no nitrite accumulation.