Microbial Community Succession Patterns And The Dynamics And Regulatory Mechanisms Of Scrippsiella Acuminata(Dinophyceae) Bloom

Harmful algal bloom(HAB)is a typical marine ecological disaster,which seriously affects the local economy,marine ecosystem,global biogeochemical cycle and even human health.In recent years,with the intensification of water eutrophication and global climate change,the scale and frequency of the development of HAB have been increasing,and HAB related research has become a hot spot in the field of environmental ecology.Although extensive studies have been carried out about the ecological mechanism of HAB,there were fewer studies on biological factors.For example,the interactions between the bloom algae and the microbial communities and the molecular mechanisms underlying the interaction between parasitic dinoflagellates and host dinoflagellates remain poorly understood.Revealing the ecological process and succession pattern of microbial communities during HAB,elucidating molecular regulatory mechanisms of HAB outbreaks is crucial to understanding the environmental drivers of the outbreak,and can provide key technical support for the early diagnosis,prediction and prediction of HAB.In this paper,we used 16S/18S rRNA/rDNA amplicon high-throughput sequencing combined with metatranscriptomics to investigate the composition,metabolic potential,driving factors and community assembly mechanisms of microeukaryotic plankton and bacterioplankton were analyzed during the occurrence,development,maintenance and demise of a HAB that occurred in a coastal ecosystems in Fujian Province.Meanwhile,the molecular mechanism of the interaction between the parasitic dinoflagellate Amoebophrya spp.and Scrippsiella acuminata was analyzed during HAB.The main results of this paper are as following:(1)The HAB event caused a decrease in microeukaryotic plankton community diversity and an increase in community homogeneity;the response of RNA-based community diversity to HAB outbreak was faster than DNA-based community,while DNA-based community diversity was faster to respond to the pre-and post-HAB conditions.The community structures of microeukaryotes showed significant changes during HAB,the main taxa with strong potential metabolic activity(characterized by RNA:DNA ratio)including dinoflagellates,Cercozoa,Chlorophyta,alveolata,Diatoms,and they had the highest relative metabolic activity during the algal bloom stages.Whether based on DNA or RNA,during the algal bloom stages,stochastic process played a dominant role in the community assembly;during the non-bloom stages,deterministic process played a dominant role in the community assembly.The HAB event enhanced the influence of the stochastic process(drift and homogenizing dispersal)on microeukaryotic plankton communities during the algal bloom stages.(2)There were significant differences in the response to HAB events between freeliving(FL)and particle attached(PA)bacterioplankton community diversity.The adiversity of the FL bacterioplankton community showed a continuous decreasing trend,and the a-diversity of the PA bacterioplankton community showed a trend of increasing first and then decreasing.FL and PA bacterial communities had strong responses to HAB event,both showing distinct succession patterns;the main taxa included Rhodobacteraceae,Flavobacteriaceae and SAR86_clade.During the HAB outbreak(MB),the PA bacterial community displayed a more pronounced cellulolysis activity,while the FL community had a more intense fermentation.Both FL and PA bacterioplankton community were dominated by the deterministic process,and HAB event enhanced the influence of the deterministic process(heterogeneous selection)on bacterioplankton communities.(3)During the HAB event,the gene expression of S.acuminata showed significant changes,mainly impacting genes involved in cytoskeleton function,energy metabolism and defense mechanism.The interaction between S.acuminata and Amoebophrya spp..also caused significant changes in the gene expression of Amoebophrya spp.,mainly involving genes related to cell recognition,energy metabolism and stress response.Genes related to energy metabolism in S,acuminata and Amoebophrya spp.were both upregulated in the non-bloom stages,reflecting a high energy cost required for defense in S.acuminata and the high energy requirements of Amoebophrya spp.for cell development and reproduction.The expression of genes in S.acuminata related to defense mechanism and genes related to infection in Amoebophrya spp.were both high during the algal bloom stages,reflecting the attack and defense interaction between the parasitic dinoflagellate Amoebophrya spp.and the host dinoflagellate S.acuminata.In conclusion,Amoebophrya spp.played a significant role in the outbreak and elimination of S.acuminata bloom.