Screening Of Nitrite Degrading Strains In Aquaculture And Its Effect On Water Environment Microflora

Accumulation of nitrite is one of the main causes of aquaculture water pollution and an important environmental factor inducing aquatic animal explosive diseases.In aquaculture,the strains of biological denitrification are mainly nitrifying and denitrifying bacteria and anaerobic ammonium oxidation bacteria.In addition to the above bacterial strains,yeast,as an excellent environmental pollutant degradation strain,has been studied by scholars.It not only plays an important role in the wine industry,but also has been more widely used in the treatment of all kinds of sewage,the utilization of waste and the remediation of contaminated soil.However,from the available patents and literature,there are few detailed reports of yeast as a nitrite removal strain.1.A dominant strain with high nitrite degradation efficiency was selected from the8 strains stored in the laboratory,which was temporarily named WP-1.Through the fermentation test of sugar,assimilation test of carbon source and assimilation test of nitrogen source,as well as phylogenetic analysis of 18S r DNA sequence,The strain WP-1 was identified as Wickerhamomyces anomalous.The strain of this study was stored in China Typical Culture Preservation Center(CCTCC)in January 2021,and the collection number was(CCTCCM2021030).2.The single factor experiment was used to study the culture conditions of the strain.The results showed that the growth rate of the strain was the fastest when the temperature was 30?,and the content of the strain was 1.21×10⁹cells/m L when the temperature was48 h.When the p H was 6,the strain grew fastest,and the strain content at 48 h was7.98×10⁸cells/m L.When glucose was used as carbon source,the strain had the best growth condition,and the strain content reached 9.86×10⁸cells/m L at 48 h.When the C/N ratio was 20/1,the growth rate of the strain was the fastest,and the strain concentration at 48 h was 10.72×10⁸cells/m L.The ability of the strain to degrade NO₂?-N and NH₄⁺-N was studied by single factor and response surface analysis.The results showed that strain could degrade nitrite nitrogen and ammonia nitrogen at 30?,and the degradation rate of NO₂?-N and NH₄?-N was 86.9%and 82.9%,respectively.When the optimum p H of strain was 6,the degradation rate of NO₂?-N and NH₄?-N was the highest,which was 83.8%and 77.7%,respectively.When the rotation speed was 120 r/min,strain WP-1 had the highest degradation efficiency of NO₂?-N and NH₄?-N was 85.5%and 79.5%.The model Y=90.52+0.20X₁-0.038X₂+0.71X₃-0.22X₁X₂+0.18X₁X₃+0.1.4X₂X₃-3.51X₁²-3.89X₂²-1.84X₃² was established by response surface Box-Behnken test(P<0.0001significantly;Lack of fit P>0.05 is not significant),which indicates that the model has high reliability;Adjusted the determination coefficient R²Adj=0.9727,it showed that the degradation rate of WP-1 was 97.30%due to different culture temperature,p H value and different culture speed.3.The content of nitrite nitrogen in samples was monitored by bacterial strain.The results showed that the degradation rate of nitrite nitrogen in the experimental group reached 95.4%,and the content of nitrite nitrogen in the control group increased significantly at the same time(P<0.05).4.The changes of bacterial community structure in experimental ponds and control ponds were analyzed by using high-throughput sequencing technology.According to the results of the bacterial community composition of"family"and"genus"of the sample,before and 12 h after the application of WP-1 strain,the dominant bacterial community in the water of the experimental pond was Vibrio,and the secondary dominant bacterial community was Alteromonadaceae.The number of Vibrio in group A-1 and A-2 before WP-1 and in group A-3 within 12 h after WP-1 was 68%,68%and 64%,respectively.The number of Vibrio A-4 and Vibrio A-5 in the groups of 24 h and 36h after sprinkling WP-1 strain accounted for 3.01%and 2.66%of the total bacteria in the system,respectively.After cultured water was treated with WP-1 strain for 24 h,the dominant bacteria group was Rhodobacteraceae,and the secondary dominant bacteria group was Flavobacteriaceae.In order to further compare and explain the species diversity difference in cultured water samples before and after using strain WP-1 in the experiment,rank-abundance curve and dilution curve were analyzed.The analysis showed that the richness of the samples before treatment was higher than that after treatment,but the species diversity of the samples after treatment was much higher than that before treatment,and the distribution of species in the samples was more uniform.In this paper,the types of nitrite degrading strains were identified.After the optimization and degradation characteristics of strains were studied,it was confirmed that WP-1 strain could effectively degrade nitrite.The change of nitrite content in the pond was monitored by WP-1 strain and the influence of WP-1 strain on the bacterial community structure in the aquaculture pond was explored.The effect and significance of WP-1 strain on aquaculture were preliminarily revealed.