| This paper focused on the activities of nitrate reductase and nitrite reductase of Paracoccus denitrificans and its inorganic nitrogen control for aquaculture water under different dissolved oxygen conditions. The results showed that Paracoccus denitrificans was an aerobic bacteria, and when carbon sources and three different forms of inorganic nitrogen coexistenced in water, the concentration of DO determined the rate of cell growth and the transformation efficiency of inorganic nitrogen. The higher the DO concentration, the faster the growth, the bigger the cells biomass. Paracoccus denitrificans had good conversion efficiency for different forms of inorganic nitrogen, it always transformed NH+4-N via assimilation, while almost transformed all NO-3-N and NO-2-N via denitrification. The degree of denitrification depended on the vitality of in vivo dissimilatory nitrate reductase and nitrite reductase of Paracoccus denitrificans. And the vitality of these two enzymes was significantly affected by the concentration of NO-3-N, NO-2-N and DO. Judging from the aspects of conversion rate and efficiency, the concentration of water DO should be kept at least 3.6 mg·L-1. Paracoccus denitrificans（viable counts≥109·mL-1） was used to control the nitrogen pollution of aquaculture water , when the concentration of Paracoccus denitrificans in aquaculture water reached to 0.75 mg·L-1, 1.50 mg·L-1 and 2.25 mg·L-1, the NH+4-N of aquaculture water decreased by 39.71%~49.33%, NO-2-N decreased by 50.00%~64.39%, NO-3-N decreased by 44.44%~60.00%, CODMn decreased by 7.81%~21.49% within 38 days. The results indicated that Paracoccus denitrificans could effectively control nitrogen and organic pollution of aquaculture water. The details of the aerobic denitrification of Paracoccus denitrificans provided a new idea for nitrogen removal of aquaculture water. |
