Isolation And Identification Of Photosynthetic Bacteria And Optimization Of Fermentation Conditions And Their Application In Aquaculture

With the rapid development of China's freshwater aquaculture industry,high-density,intensive and industrialized aquaculture models have caused serious pollution to the aquaculture environment.The residual bait,excrements of aquatic animal,and accumulation of planktonic residues have caused the excessive accumulation of inorganic tri-state nitrogen in the aquaculture water,which will endanger the health of aquatic animals and inhibited the development of aquaculture.The unique metabolic pathway of photosynthetic bacteria in the probiotic preparation could effectively remove inorganic tri-state nitrogen in the aquaculture water,increase the dissolved oxygen content in the aquaculture water,and purify the aquaculture water,which has broad development prospects.In this study,two photosynthetic bacteria HG315-1 and HG315-2 were separated and selected from the bottom mud of the freshwater breeding base by the double-layer plate method.The strains HG315-1 and HG315-2 were identified through physiological and biochemical experiments and 16S r DNA sequence determination.And then the growth of the two strains in the simulated sewage with ammonia nitrogen,nitrite nitrogen and nitrate nitrogen as the only nitrogen source was discussed.Finally,the strains with better performance in the simulated sewage experiment were combined with nano-iron tetroxide to establish a high-density rapid fermentation technology,and applied to the local anchovy aquaculture,to explore its water purification effect in the anchovy aquaculture.Through physiological and biochemical experiments and 16S r DNA sequencing,the strains HG315-1 and HG315-2 were identified as purple non-sulfur bacteria,Rhodobacter sp.and Rhodobacter capsulatus.The optimization of culture medium and culture conditions showed that the optimal medium formulation of strain HG315-1 was sodium acetate 3.5 g/L,ammonium chloride 0.5 g/L,yeast extract 2.5 g/L,and potassium dihydrogen phosphate 0.9 g/L,Magnesium sulfate 0.5 g/L,trace element 1 m L,growth factor 1 m L,p H 8.0.the optimal medium for strain HG315-2 is sodium acetate 3 g/L,ammonium chloride 0.7 g/L,yeast extract2.5 g/L,dipotassium hydrogen phosphate 0.9 g/L,magnesium sulfate 0.5 g/L,trace element 1m L,growth factor 1 m L,p H 7.0.Experiments on the removal of inorganic tri-state nitrogen in simulated sewage show that:HG315-1 and HG315-2 both had a high ability to remove ammonia nitrogen.When the ammonia nitrogen concentration is 29.69 mmol/L,the removal rates of ammonia nitrogen are 81.88%and76.7%,respectively.HG315-1 and HG315-2 can tolerate a certain concentration of nitros nitrogen.When the concentration of nitros nitrogen is 13.54 mmol/L,the removal rates of nitros nitrogen are 68.18%and 58.82%,respectively.HG315-1 and HG315-2 has the best effect on nitrate removal.When the nitrate concentration is 19.12 mmol/L,the removal rates of nitrate are91.83%and 100%,respectively.The results of purification experiment of the aquaculture water of anchovy showed that the nano-iron ferric oxide modified by Cetyltrimethylammonium bromide(CTAB)combined with photosynthetic bacteria HG315-1 carried out high-density rapid fermentation,the fermentation concentration was increased by 14.6%,and the concentration of bacterial cells reached 2×10~9?/cfu,sprinkled at 1 kg/mu in the anchovy farming pond to reduce the concentration of ammonia and nitrous nitrogen in the aquaculture water by about 90%,stabilize the p H of the aquaculture water,increase the dissolved oxygen in the aquaculture water,and increase the transparency of the aquaculture water about 6 cm.This research will broaden the application prospects of photosynthetic bacteria in the aquaculture.