Biogeographic Distribution Of Marine Viruses And Its Driving Processes In Typical Estuaries And Coastal Marine Environments Of China

Marine viruses are the most abundant and diverse biological entities in the ocean.Viruses release a large number of dissolved organic matters into seawater by infecting and lysing host cells,thus changing the nutrient and energy cycles of the marine food web.By infecting the host,viruses play an important role in regulating the community structure,diversity and evolution of organisms.Viral ecology is the rapidly progressing area of research,as molecular methods have improved significantly for targeted research on specific viral populations and whole communities.Exploring the occurrence and mechanisms of the biogeographic patterns of marine viruses understanding marine virus-host interactions and the mechanisms that influence microbial community composition.China has a vast coastal offshore area and numerous estuaries.River diluted water flows through the shelf into the ocean water,the complex hydrological environment leads to a diverse biological diversity.However,the research on viral communities in China estuary and coastal areas is limited nowadays.Here,we investigated the structure,diversity and drivers of viral community in the China estuary,shelf and open sea,based on viral signature genes using high throughput sequencing,which will broaden our understanding of viral community structure and ecological processes in China estuarine and coastal areas.The main conclusions of our study include:1.T4-like myovirus is a significant fraction of the viral community,and exists in a wide variety of environments(ocean,paddy,lake and estuary environment,etc.),occupying an important ecological niche in the ecosystem.We amplified the relatively conserved g23 gene(encoding capsid protein)of T4-like viruses,and studied the changes of T4-like viral community structure in salt and mixture of fresh and salt water from four typical estuaries in China(Yellow River Estuary,Yangtze River Estuary,Qiantang River Estuary and Pearl River Estuary)and in the estuary-shelf-ocean transect of the northern South China Sea.T4-like virus includes Marine Group,Estuary Group,Paddy Group and Lake Group.Marine Group includes the Marine group Ⅰ-Ⅴ and the cyanophage that infects cyanobacteria.Marine group Ⅰ and Ⅳ had a wide distribution in salt and mixture of salt and fresh water from the four typical estuaries in China as well as the continental shelf and open sea environment in the northern South China Sea.Marine group II and III prefer to lower-salinity continental environment,while Marine group V were abundant in the eutrophic environment.We also found that there are many factors affecting the spatial distribution of viruses,such as temperature,salinity and heterotrophic bacterial abundance,etc.Moreover,the influence of environmental factors presents seasonal differences.2.The structure and mechanisms of the community of T4-like virus and cyanophage were investigated in the estuary-continental shelf-open ses transect of the northern South China Sea,based on g23 gene and g20 gene(encoding portal protein),respectively.We found that both T4-like viruses and cyanophage showed obvious geographical distance-decay patterns,which were mainly drived by selection(heterogeneous selection),though there present a certain influence by dispersal process.Among environmental selection factors,the bacterial community structure alone exerted almost the same degree of selective pressure as other abiotic and biotic variables in shaping viral community.Network analysis suggested that bacterial community composition may impact viral community assembly and biogeography through diverse ecological interactions,such as lysis,co-infection and mutualism.In addition,the results of the assembly process affecting the specific viral community based on different significant genes suggested that heterogeneous selection might be the main process in driving the whole viral community in the northern South China Sea,and the host community structure plays an important role within the selection.Moreover,we found that low abundance groups within T4-like viral community and cyanophage community,play an important role in these two viral community assembly.3.Particle attached is the important fate of viruses in marine aquatic environment.We found that there were significant differences in the distribution of free-living(FL)and particles-attached(PA)T4-like viral community in the East China Sea.In addition,the diversity of large 0.8 PA(0.8-3 μm)and FL T4-like viral community is higher than that of small 0.2 PA(0.2-0.8 μm)T4-like viral community.Although the relative contribution of different factors to the assembly of FL and PA viral community were different in the East China Sea,environmental selection was the main driver.Bacterial community composition showed the greatest influence on the community composition of 0.8 PA viruses,and there was almost no common explanation for the environmental and spatial variables in assembly the large 0.8 PA viral community,suggesting that the characteristics of particle microhabitat had an impact in shaping 0.8 PA T4-like viral community.It also indicated that more comprehensive particle biochemical characteristics and chemical composition should be included in the subsequent ecological studies of particle-attached viruses.