Nitrification Characteristics Of A Nitrite-oxidizing Bacteria Enrichment Culture Suitable For Freshwater Aquaculture Water

The problem of nitrite in aquaculture water has become increasingly prominent.Nitrification is an important process for the removal of nitrite in aquaculture water.Nitrite oxidizing bacteria are the main bacteria to remove nitrite in water,but they are extremely sensitive to environmental conditions,they grow slowly,it is difficult to form dominant species in the natural environment.In order to understand the role of nitrite-oxidizing bacteria in aquaculture water and increase the removal rate of nitrite in aquaculture water through bio-enhancement,this article investigated the bacteria in freshwater aquaculture water in spring and summer.The relationship between community structure and nitrification rate.An enriched culture of Nitrobacter(XY-12)was isolated and screened from freshwater aquaculture waters.The optimal culture conditions and nitrite oxidation activity were explored.Nitrification activity tests were carried out in different aquaculture waters,and the immobilization process was preliminary explored.The specific research results are as follows:16S rDNA high-throughput sequencing technology was used to analyze the bacterial community structure in spring and summer in 15 freshwater aquaculture waters(three types),and the in-situ nitrification activity was determined.It was found that nitrite-oxidizing bacteria in freshwater aquaculture waters in spring and summer accounted for less than 0.05%of the total bacterial count.Nitrite-oxidizing bacteria have different dominant genera in spring and summer.In spring,Nitrotoga was dominant,and Nitrospira was dominant in summer.Among them,Nitrobacter and Nitrospira were significantly positively correlated with nitrification rate(P<0.05).A kind of nitrite-oxidizing bacteria enrichment was obtained from freshwater aquaculture waters through continuous enrichment and dilution purification methods.The enrichment contains only one kind of NOB,and the proportion is 99.1%,according to 16S rDNA and Nxr A genes,the similarity between NOB in the enrichment and Nitrobacter Vulgaris was 100%.The influence of temperature,p H,nitrite,nitrate and salinity on its growth were studied.NO₂^--N removal abilities in freshwater aquaculture water and brackish water circulating aquaculture water were tested.The results showed that the optimum temperature of N.Vulgaris XY-12 was 27??30?,the optimum p H was 7.5,and the optimum salinity was 0.38%.The half inhibitory concentrations of nitrate and salinity on XY-12 were 400 mg L^-1and 0.63%,respectively.The optimum growth NO₂^--N concentration were 200 mg L^-1.Under the optimal conditions,the shortest generation time of N.Vulgaris XY-12 was 12±2 h,and the maximum nitrite removal rate was 1.62 mg L^-1h^-1.In different types of aquaculture water,the shortest generation time was 13.1 h,and the maximum nitrite removal rate was 0.077 mg L^-1h^-1.The immobilization process was used to compare the immobilization effects of N.vulgaris XY-12 on three carriers,and it was found that the biological filler S type could remove 20 mg L^-1NO₂^--N in the medium within three days.In aquaculture water,the biological filler S-type could enhance the nitrification rate of N.vulgaris XY-12,and its removal rate could reach up to 85%.In summary,It was found that the abundance of nitrite-oxidizing bacteria in freshwater aquaculture water was extremely low,and Nitrobacter played an important role in nitrite oxidation.N.vulgaris XY-12 enrichment culture was isolated from freshwater aquaculture water and has high adaptability to the environment,its growth rate was fast,and it was suitable for different types of aquaculture water.