Screening Of Denitrifying Bacteria And Its Applying In Aquaculture

In recent years, the aquaculture industry of our county had a rapid development, intensive andfactory farming becomes the trend of development gradually. However, under this intensivefarming condition, high nitrite nitrogen had become the outstanding issues, resulting a series ofdiseases and environment problems, restricting the development of the aquaculture industry. So,how to solve the high nitrite nitrogen is imminent.To remove the nitrite nitrogen was the primary targets of this study. The sample got from thebottom of the mariculture shrimp pond, then enriched, isolated, purified and screened thedenitrifying bacteria with the high ability of removing nitrite nitrogen. A strain of bacterium, strainFP6, with the high ability of removing nitrite nitrogen was selected to carry out the following work:identified the strain based on the sequence of the16S rRNA gene and physiological andbiochemical properties; factors that affected the denitrifying ability of the strain were investigated,including carbon sources, C/N ratio, initial pH, temperature, shaker speed and NaCl concentration.Moreover, the ability to remove ammonia and nitrate of the strain was also studied; the nitrogenremoval effect of the strain combined with sucrose under the simulations of seawater andfreshwater farming. Finally, we got a strain FP6with the highest ability of removing nitritenitrogen, it could completely remove25mg/L nitrite nitrogen in48hours, total nitrogen removalrates was about26percent. The similarity of the strain FP6with the Bacillus licheniformisATCC14580（T）was98.25percent, combined with the physiological and biochemical propertieswe preliminary judgment that it belonged to Bacillus licheniformis.Sucrose was identified as thebest carbon source for its growth and denitrification. Under the conditions of C/N ratio15－25,initial pH7－10, temperature20℃－37℃, shaker speed0－200r/min and NaCl concentration0－40g/L, strain FP6kept high removing nitrite nitrogen ability. Strain FP6showed the ability ofremoving ammonia and nitrate and no nitrite nitrogen was accumulated when removing nitrate.The nitrogen removal effect of the strain combined with sucrose under the simulations of seawateror freshwater farming was well. When applied with photosynthetic bacteria, its had the ability ofremoving ammonia nitrogen and nitrite nitrogen, the nitrite nitrogen was10to20percent lowerthan the controls, even in intensive farming, and the effect was the same or even better than themicroorganism preparation of commercially available product. However, the removal efficiency of nitrite nitrogen was not so well that to meet the requirement of the reality. Further research of theproperty of the strain and the applying conditions were still needed.