Effects Of Micro-ecological Bacteria On Water Quality And Microbial Community Structure Of Fish Aquaculture Water

The development of intensive freshwater aquaculture has led to the accumulation of nitrogen and phosphorus in aquaculture waters,which is easy to cause eutrophication and damage the ecosystem balance of aquaculture waters.In addition,ammonia nitrogen,especially nitrite nitrogen,can cause potential toxicity to aquaculture organisms and bring great economic losses to the aquaculture industry.Therefore,ammonia nitrogen,nitrite nitrogen,phosphorus and so on in aquaculture waters have been widely concerned.In order to find a strain with better degradation effect on aquaculture water,this experiment studied the degradation effects of Bacillus Subtilis(BS),Bacillus Coagulans(BC),Bacillus megaterium(A0)and their different combinations A0+BC+BS(M)?A0+BC?A0+BS?BC+BS(composited by equal volume)on ammonia nitrogen,nitrite nitrogen,nitrate nitrogen and total phosphorus in fish culture water.The experiment was carried out for 15 days and the amount of bacteria added was 1.5‰(2.0×10~8cfu/mL).The results showed that Bacillus megaterium could significantly reduce ammonia nitrogen,nitrate nitrogen and total phosphorus(p<0.005);Bacillus subtilis had a significant effect on nitrite nitrogen degradation(p<0.005).Compared with Bacillus megaterium,A0+BC had a more significant effect on ammonia nitrogen and nitrate nitrogen degradation(p<0.005),the 7d ammonia nitrogen removal rate was 75.7%and the content of which was always significantly lower than the control,the 13d nitrate nitrogen removal rate was 27.8%.The results indicated that the combination of A0 and BC showed mutual promotion for the removal of ammonia nitrogen and nitrate nitrogen;Compared with Bacillus subtilis and Bacillus megaterium,A0+BS had the best degradation effect on nitrite nitrogen and total phosphorus(p<0.005),the nitrite nitrogen removal rate was93.4%on the 15th day.On the 7th day,the total phosphorus removal rate was 76%,and the content was always significantly lower than that of the control,which indicated that the combination of BS and A0 showed synergistic effect on the removal of nitrite nitrogen and total phosphorus.In summary,A0+BC has the best degradation effect on ammonia nitrogen and nitrate nitrogen;A0+BS has the best degradation effect on nitrite nitrogen and total phosphorus,and the degradation effect of the two strains is better than that of the single strain and the three strains.In order to explore the effects of the best composite strains A0+BC and A0+BS on the N?P and micro-ecological environment of fish culture water,high-throughput sequencing was used to study the dynamic changes of microbial community structure in fish culture water.The results showed that the diversity of the mixed strains A0+BC and A0+BS water samples increased and A0+BS diversity was higher than A0+BC.Compared with the water sample CK,the Firmicutes of A0+BC and A0+BS water samples disappeared,the Actinetobacteria appeared,the Proteobacteria increased and Bacteroidetes decreased.From the classification level of the class,compared with the water sample CK,Alphaproteobacteria,Gammaproteobacteria and Betaproteobacteria were the dominant bacteria and the proportion of which increaed in the A0+BC?A0+BS waters,which was related to the removal of ammonia nitrogen,nitrate nitrogen and nitrite nitrogen by A0+BC and A0+BS bacteria.At the taxonomic level of the genus,the microbial community diversity of the aquaculture water was high.Compared with the water sample CK,Lysinibacillus disappeared and Comamonasin?Stenotrophomonas increased in the A0+BC and A0+BS water samples,which promoted the degradation of nitrogen in aquaculture water.In addition,the other dominant Pseudomonas in the A0+BC water sample was of the denitrification type,which promoted the degradation of nitrate nitrogen.The other dominant bacteria in the A0+BS water sample was Bosea,which promoted the removal of nitrite nitrogen.The compound strain A0+BS has the best degradation effect on nitrite nitrogen and total phosphorus,increasing the microbial diversity of fish culture water and inhibiting pathogenic bacteria to some extent.In addition,according to the safety classification list of strains in the General Technical Guidelines for Biosafety of Microbial Fertilizers(NY1109-2006),the two strains belong to the strains that are free of toxicological tests,ensuring the safety of both.Therefore,A0+BS is selected finally as a highly effective composite fungicide that can be applied to freshwater fish farming.With comprehensive economic and environmental benefits,it is recommended that the interval of bacterial dosage is 13d-15d.