Screening And Application Of Ammonia-Degrading Bacteria In Symphysodon Haraldi Culture Water

At present,the cultivation of Symphysodon haraldi in China mainly relies on indoor recirculating aquaculture,which has the advantages of environmental protection and low cost.However,under closed conditions,the ammonia nitrogen concentration in recirculating aquaculture will often be too high.At the same time,discus fish likes cow heart hamburger and red worms and other bait.The impact of live bait on water quality is even more serious.In order to solve this problem,this research studied the bacterial community structure and water quality indexes of discus fish water.(1)This research investigated the changes of water quality elements and microbial community pattern in short-term aquaculture of discus fish.The result showed that the correlation between the microbial community of the water body on the 0 day and the water quality indicators of various nitrogen forms was not large,but with the passage of time,the microbial community of the water body on the 1st and2nd day showed a positive correlation with nitrate.On the 3rd and 4th day,the microbial community in the water body has a great correlation with various nitrogen forms,especially nitrous and ammonia nitrogen.In the water quality change,the correlation between nitrous and ammonia nitrogen is relatively large;the greatest correlation.In the process of discus fish aquaculture,water quality indicators are closely related to the health status of the discus fish.The structure and temporal and spatial changes of bacterial population in the water of discus fish culture were analyzed by 16S r RNA sequencing technology.In terms of the abundance of microbial species in the aquaculture water environment of discus fish,406 sequences were detected at the OTU level.Proteobacteria and Bacteroidete were the dominant phyla in water microorganisms over time,especially Proteobacteria,whose abundance increased rapidly on day 1.From the perspective of microbial community structure,the community structure of the first 2 days and the last 3 days showed obvious separation,indicating that the microbial community structure changed significantly with the extension of culture time.This research conducted RDA correlation analysis on water quality changes and microbial communities,and found that there was little correlation between water indexes on day 0 and water quality indexes of various nitrogen forms,but on day 1and 2 showed positive correlation with nitrate nitrogen as time went by.On day 3 and4 showed great correlation with various nitrogen forms,especially nitrite and ammonia nitrogen.Nitrite had great correlation with ammonia nitrogen in water quality change.The correlation between community and ammonia nitrogen was the highest in all samples,and the heat map showed that hgcⅠ＿clade and Candidatus＿Aquiluna were different,especially bacillus.In the function prediction of bacterias,this research found some functional bacteria related to nitrogen reduction and nitrogen fixation.The exploration of these water results is convenient for us to understand the correlation between water quality indexes of discus fish and microcommunities in short-term aquaculture,and provides environmental reference for green aquaculture fish,especially ornamental fish.(2)Due to the high correlation between Bacillus and ammonia nitrogen in water,this research selected ammonia nitrogen screening medium to separate,screen and identify the bacteria in water,and finally isolated a bacterium.After morphological,physiological and biochemical characteristics identification and 16S r DNA sequencing,a bacterium with ammonia nitrogen degradation function was finally determined.Bacillus cereus.The safety test results showed that bacillus cereus strain had no toxic effect on cultured discus fish.The experimental results of water purification showed that the bacterial strain could degrade ammonia nitrogen and nitrite in simulated sewage after 4 days,indicating that the bacillus cereus strain had obvious effect on water purification,which could provide a basis for reducing the high ammonia nitrogen content in the process of discus fish culture with ecological agents.(3)This research added the screened Bacillus cereus B6 into the cultured water of discus fish with concentrations of 1x10~6cfu/m L,1x10~7cfu/m L and 1x10~8cfu/m L,respectively.After 7 days of cultivation,the water quality indexes were determined again,and the results showed that:Under the maximum concentration of1x10~8cfu/m L,the degradation rate of ammonia nitrogen reached 70%,nitrite nitrogen reached 74%,and nitrite reached 91%.This proves that bacillus does indeed have a potential nitrogen reducing effect.At the same time,this research conducted high-throughput sequencing on the water microbial community after the end of culture again,and the results showed that the species richness and diversity index analysis at the OTU level showed that there was no significant difference in Alpha diversity between the three different concentrations of Bacillus cereus B6 test group and control group.The changes of diversity Ace,Shannon and Shannoneven were not significant.The dominant bacteria at phylum level in the four groups were Proteobacteria,Bacteroidetes,Actinobacteriota,Firmicutes and so on.Compared with the control group(K)and the other two experimental groups(A and B),the proportion of Firmicutes in the highest concentration group(C)increased rapidly,reaching 43.55%,forming the dominant flora in water bodies.At the genus level,the proportion of Bacillus in test group(C)was the highest,and the proportion of bacillus in the other three groups was relatively low.The abundance of Flavobacterium was higher in all four groups,and the proportion was similar.PCo A results showed that the microbial structure of bacillus cereus B6 with 10~8cfu/m L was significantly separated from that of other groups.These structures elucidate the disturbance and change of bacillus on water microbial community structure,and may also verify the interaction between microorganisms and water indicators,providing new insights and ideas for the improvement and promotion of the water body foe the aquaculture of the discus fish.