[Identification and characteristics of a marine aerobic denitrifying bacterium].

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.