Succession of Bacterial Communities in Biofilters of the Mud Crab Recirculating Aquaculture System
[Objective]This study is to investigate the succession of bacterial communities in the biofilter of recirculating aquaculture system(RAS),to find a biofilter suitable for RAS culture of mud crab(Scylla paramamosain).[Method]Water quality of the RAS tanks were monitored on days 2,5,10,20,30,40,and 50.Samples of biofilm on filter media and microbiota in the cultivation tank water were collected.Various bioinformatics analysis methods were employed to study the succession of microbial communities in the biofilm.Quantitative Real-time PCR was utilized to detect the copy numbers of functional genes related to carbon and nitrogen cycling in the biofilm.[Result and Conclusion]The results showed that the concentrations of ammonia nitrogen(NH4+-N),non-ionized ammonia(NH3),and nitrite nitrogen(NO2--N)exhibited an initial increase a following decrease,while nitrate nitrogen(NO3--N)and total nitrogen(TN)accumulated at the end of the experiment(Day 50).Total organic carbon(TOC)concentration remained stable before day 10,butsignificantly increased and significantly decreased from day 10 to day 50(P<0.05).The concentration of total nitrogen(TN)and nitrate nitrogen(NO3--N)had the greatest impact on the change of biofilm bacterial community.The diversity,uniformity,and richness of bacterial communities in the biofilm peaked at day 10 and then reached a steady state.Functional prediction based on FAPROTAX revealed enrichment of nitrogen cycling and organic matter degradation functions in the biofilm.Absolute gene copy numbers of carbon and nitrogen cycling in the biofilm showed an increasing trend over time.According to FEAST analysis,bacterial contributions from the water to the biofilm were higher before day 20 except day 10,while contributions mainly originated from earlier biofilm after day 30,and the contribution rate increases with time and tended to be stable in the later stage.This study indicates significant temporal changes in both the structure and function of bacterial communities in the biofilm during the startup process of the RAS for mud crab cultivation,the function of biofilm bacteria is mainly concentrated in nitrogen cycling and organic matter degradation.The contribution rate of biofilm bacteria from their own bacteria also gradually increases,and tends to be stable in the later stage.
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