Taxonomic And Functional Diversity Of Microbial Communities In Typical Coastal Marine Environments

Marine microbes play a crucial role in the marine biogeochemical cycling.Their ecological function has a close relation with their community structure.The great diversity of microbes has been demonstrated in the ocean ecosystem by the development of the molecular biology technology.The structure and diversity of the microbial community is affected by the marine environment including physicochemical and biological factors.Thus,it is important to understand the structure and diversity of the marine microbial community.The coastline of China is long and has a vast offshore area.The complicated hydrographic situation of coastal ocean leads to a diverse structure and function of microbial community.Since the quick development of the economy,the increased anthropogenic activity strongly influences the coastal ecosystem.Also,this change affects the structure and diversity of microbial communities in the coastal area.Therefore,a clear understanding of the structure and diversity of microbial community will help us to evaluate the influence of climate change and anthropogenic activities on this area.However,Thethe study on the microbial community in the China coastal area is limited nowadays.The East China Sea(ECS)is a typical continential shelf sea.It is located in a temporal zone and is a relatively high production offshore area in China,which is influenced by the anthropogenic activity and complex currents.However,it is not well-understood that the taxonomic diversity as well as functional diversity of microbial communities in this area.The limited studies focused on the taxonomic diversity of microbial community,while the research on the functional structure of microbial community is even more lacking.Compared to ECS,the seawater around Xiamen Island,a typical subtropical island,is under a stronger anthropogenic influence.Previous study has demonstrated that the anthropogenic activity influenced the structure of phytoplankton community.Nevertheless,the lack of the studies in this area,especially the time-series study,limits the understanding of the role of microbial communities in this area.Here,we investiaged the structure and diversity of microbial community in the ECS and seawater around Xiamen Island and their relationship with the environmental variables using the melocular ecology methods.The mainly conclusions of our study include:1.We found a close relationship between the taxonomic and functional structure of microbial communities and the water mass in the ECS through a high-throughput metagenomic technology.Firstly,we found that the Proteobacteria,Cyanobacteria and Bacteroidetes were the major bacterial groups in the ECS,which indicated their important roles in the ECS ecosystem.Moreover,our results revealed a higher taxonomic diversity but a lower functional gene diversity of the microbial community in the surface seawater compared to the bottom seawater.A different preference in substrate of microbial communities was found between surface and bottom seawater.The microbial communities preferred to utilize the liable organic matters in the surface seawater,while ones in the bottom seawater preferred to the relatively recalcitrant organic matters.Meanwhile,we found a high function redundancy via a shotgun metagenomic analysis.These results might relate to the hydrographic situation,which is more complex in the surface but relatively stable in the bottom.The statistical analysis revealed that the diversity of microbial community associated with the temperature and salinity at horizontal scale,indicating that the different currents also strongly affected the microbial communities.2.The physicochemical attributes of seawater around the Xiamen Island shows a clear seasonal variation,especially during the summer.Similarly,the distinctly seasonal changes in structure of microbial communities were also observed by high-throughput sequencing.The a-and y-Proteobacteria?Bacillus and Flavobacteria were the major contributors to these variation.In addition,generally,the spatially-near station possessed a similar structure in one season.The structure of microbial community in the northwest was distinct from ones in the southeast,while station influenced by Jilong River discharge was different from other stations.This result might associate with anthropenic activity in the northwest(e.g.aquaculture in the Xingling Bay and Tongan Bay)and invased seawater in the southeast.Our investigation revealed that the nutrient had a close correlation with structure of microbial community by dbRDA,which indicated their importance in influencing the microbial community in this coastal area.Additionally,Roseobacteria and Bacillus revealed a close relation with the nutrients by a network analysis.Notably,as a high BBC:A ratio during summer,the anthropogenic activity might relate closely with the microbial community structure during this season.Thus,complex hydrographic situation is one of the major factorsfactor that affected the microbial community in this coastal area.Moreover,anthropogenic activity,especially the changes in nutrients,is another factor influencing the microbial community in this coastal seawater.