Screening And Studying On Characteristic Of Bacteria Used For Purifying Water Quality Of Freshwater Aquaculture

In this study, the water and soil sample were gathered from freshwater fish farm in Changsha and Yueyang Hunan.12 strains of bacteria with strong survival ability were isolated by enrichment culture, and 4 strains with high efficiency of removing COD, had been screened out after re-screening. We screened out 1 strain bacterium which has high degeneration ability of nitrite when nitrite was used as exclusive nitrogen source. Based on their morphology, physiological and biochemical characteristics as well as 16 sRNA sequencing, these 4 strains were identified as bacillus subtilis, bacillus licheniformis, Saccharomyces pastorianus and Pseudomonas stutzeri respectively.The results of the breeding carp experiment showed that these 4 strains were safe for aquaculture organisms. Antagonist experimental results indicated that there were no inhibitory effects among these 4 bacterial strains. Antibacterial experiment showed that bacillus subtilis and bacillus licheniformis had certain bacteriostasis ability to E. coli and salmonella, while Saccharomyces pastorianus and Pseudomonas stutzeri did not have the same ability.The fermentative conditions of Bacillus subtilis and Bacillus Licheniformis had been optimized and the effects of 4 kinds of conditions on Pseudomonas stutzeri including nitrite concentration, pH, temperature and inoculumconcentration were studied in this research. In the aquaculture ponds model, the characteristics of each bacterium on degradation of COD, ammonia nitrogen, nitrite and sulfide had been studied. Among the 4 strains, Bacillus subtilis had the highest degradation rate of COD and ammonia nitrogen (89.50% and 80.89%respectively); Saccharomyces pastorianus had the highest degradation rate of sulfide and its removal rate reached 75.28%; Pseudomonas stutzeri got the highest degradation rate of nitrite (98.29%).We also studied the degradation characteristics of 4 kinds of compound bacteria (B: Bacillus subtilis :Bacillus licheniformis= 1:1; C: Bacillus subtilis : Bacillus licheniformis : Saccharomyces pastorianus= 1:1:1; E: Bacillus subtilis : Bacillus licheniformis:Saccharomyces pastorianus:Pseudomonas stutzeri=1:1:1:1). The results showed that E was the best compound bacteria, whose removal rate of COD, ammonia, nitrite and sulfide were 95.82%,88.39%,84.55% and 86.51%, respectively.Compound bacteria E was selected to perform an experiment in the farm. The results indicated that compound bacteria E could improve aquaculture water quality, whose removal efficiency of COD ammonia nitrogen, nitrite and sulfide were 51.67%, 81.63%,84.4% and 78.57%, respectively.