大口黑鲈循环水养殖系统挂膜期生物膜微生物群落动态及功能菌群OACHSSCD

[Objective]This study aims to explore the dynamic and evolution pattern of biofilm microbial communities,along with those functional microbes and their roles,during the process of biofilm formation in recirculating aquaculture systems(RAS)of largemouth bass(Micropterus salmoides),so as to provide important theoretical basis for biofilm culturing and its application in RAS of M.salmoides as well as other economic aquaculture fishes.[Method]The formation of biofilm was evaluated indirectly based on changes of ammonia and nitrite content in the effluent of the biological filter,and accordingly temporal samples of the filter media at different stages(15,25,35,45 d)of biofilm formation were collected,respectively.Then,the compositions,interaction networks and phenotype characteristics of the biofilm bacterial communities in filter samples were analyzed by 16S rRNA high-throughput sequencing,microbial ecological network and BugBase phenotype prediction methods,respectively,and furthermore those functional taxa that contributed largely to the biofilm formation were revealed.[Results]In the process of biofilm formation,the bacterial communities in biofilm were composed mainly of Pseudomonadota,Bacteroidota,Chloroflex,Acidobacteriota and Nitrospirota.Alpha bacterial diversity of the biofilm community,as described by Chao 1 and Shannon indices,presented a trend of initial increase and subsequent decrease and eventual stabilization,and its beta diversity also manifested as significant changes(P<0.01)in community structure before basic stability..Taxa that significantly enriched on biofilms at different stages of biofilm formation were distinct.Specifically,taxa of Bacteroidota,Chloroflex and Pseudomonadota were enriched at the early stage,taxa of Pseudomonadota,Acidobacteriota,Nitrospirota and Deinococcota were enriched at the intermediate stage,while taxa enriched at the mature stage all belonged to Pseudomonadota.This indicated a gradually increased degree of enrichment for Pseudomonadota,and particularly its genera of Fuscovulum,Defluviimonas,Rhizobacter and Hyphomicrobium,which became a remarkable feature of biofilm maturation.The microbial network of the biofilm community became more closely related but less modular during the periods of biofilm formation,indicating community network structure turned to be more complex and integrated.And the biofilm bacterial communities harbored relatively low-abundant members rather than dominant ones as keystone taxa,especially those of Pseudomonadota which played a critical role in promoting the community network development and simultaneously maintaining the network structure stability.The change in community oxygen demand from anaerobic to facultatively anaerobic as well as the gradually increased biofilm formation ability were observed for bacterial communities during the biofilm formation,and that belong to Pseudomonadota norank_f__Hyphomicrobiales,Defluviimonas,Rhizobacter and Hyphomicrobium are the main members that affected the phenotypic change of the community.[Conclusions]In conclusion,significant dynamic changes were observed for biofilm bacterial communities in the process of biofilm formation in recirculating aquaculture systems of largemouth bass(M.salmoides),and Pseudomonadota were considered the core taxa that drove the community structural and phenotype functional change and promoted the biofilm maturation.