Community Structure And Assembly Process Of Bacteria And Archaea In Typical Waters Of Taihu Lake

As a large and shallow lake,Lake Taihu is the third largest freshwater lake in China.Different zones have distinct degree of eutrophication and unique ecological environment characteristics,providing nutrient-rich conditions for microorganisms.Bacteria and archaea play key roles and make great contributions to the food web,nutrient and energy flow of the lake ecosystem.Community assembly mechanism is a core topic of microbial ecology,having very important research significance.Microorganisms in water can be divided into two different life styles: Free-living(FL)and Particle-associated(PA)according to the particle size,are playing different roles in the process of material cycle.Therefore,it was of great significance to study the microorganisms of different life styles in Lake Taihu and our aims are to determine 1)the temporal and spatial distribution pattern,community composition and diversity of both bacteria and archaea communities in different life styles,2)the relationship between community composition and environmental factors,and 3)the formation mechanism of the community.In this study,the water body of Lake Taihu was selected as the research object,and combined high-throughput sequencing with molecular bioinformatics analysis methods to determine the composition of microbial communities in different life styles.The contents and results are as follows:1.The spatial and temporal distribution characteristics of bacterial and archaea community structure in typical regions of Lake Taihu.(1)We amplified the 16 S rRNA genes of bacteria and archaea,using high-throughput sequencing and real-time fluorescence quantitative PCR to study the temporal and spatial distribution characteristics,absolute abundance and environmental factors of bacteria and archaea communities in three seasons(spring,summer and autumn)and different sampling sites(Zhu Shan Bay,Fudu Port,Xukou Bay,Gonghu Bay,East Lake Taihu).The results showed that the composition of microbial community showed different characteristics of temporal and spatial distribution.The community distribution varies with the season.In the FL community,the relative abundance of Cyanobacteria in bacteria and Crenarchaeota in archaea were particularly prominent.In the PA community,the relative abundance of Cyanobacteria and Actinobacteria varied significantly with seasons,while the relative abundance of archaea was stable.Euryarchaeota,Crenarchaeota and Thaumarchaeota were always the dominantors.The relative abundance of different groups of microorganisms showed different spatial distribution characteristics.In FL community,it was obviously that the relative abundance of Actinobacteria in bacteria were higher in Gonghu Bay(45%)than other sites,and Bacteroidetes had high relative abundance in East Lake Taihu(28%).As for archara,Thaumarchaeota had the highest relative abundance in East Lake Taihu(70%),and the lowest in Fudu Bay(12%).Crenarchaeota had a higher relative abundance in Zhushan Bay(27%).Euryarchaeota had a high relative abundance in Fudu Port(51%).In PA community,Cyanobacteria were higher in Gonghu Bay,Zhushan Bay and Fudu Bay(28%,33%,33%),where has heavy eutrophication,and lowest in Xukou Bay(11%),where the eutrophication was not heavy.Proteobacteria had the highest relative abundance in Xukou Bay(47%),while Crenarchaeota was highest in Zhushan Bay(49%)but lowest in Fudu Port(19%).The relative abundance of Euryarchaeota were higher in Fudu Port(72%)than other sites.(2)In the typical area of Taihu Lake,the analysis of community diversity showed that the the richness of ?-diversity in bacteria was the highest in spring.As for archaea community,the ?-diversity of archaea community in spring was the lowest.There was no significant difference in ?-diversity at different sites both of bacterial and fungal communities(P>0.05).The results of ?-diversity and ANOSIM analysis showed that the influence of seasonal factors on the diversity of bacterial was significantly in Lake Taihu.However,archaea showed significant difference in both temporal and spatial distribution in Lake Taihu.2.The microbial community structure and microbial community assembly of different life styles in Lake Taihu.(1)The community structure of Lake Taihu was analyzed by high-throughput sequencing at different depths(0-50 cm,50-100 cm,100-150 cm and 150-200 cm).In summary,there were 39 bacterial phyla and 10 archaeal phyla in the water body during summer.Bacterial and archaeal communities showed a specific microbial composition in the Lake Taihu ecosystem.Bacteria was mainly composed of Proteobacteria,Bacteroidetes,Actinobacteria,Cyanobacteria,and so on.Archaea was mainly composed of Euryarchaeota,Crenarchaeota,Thaumarchaeota,Diapherotrites,Nanoarchaeaeota and etc.Bacteria and archaea in Lake Taihu were specifically distributed according to different life styles.The abundance of Cyanobacteria in the PA community was higher than that of FL,and its relative abundance decreases with the increase of lake water depth.The abundance of Actinobacteria in the FL community was higher than that of the PA.The relative abundance of Nanoarchaeaeota and Diapherotrites in the FL was much higher than that of the PA community.Except for Fudu Port,the relative abundance of Crenarchaeota in the PA community was much higher than that in the FL community.According to the results of?-diversity of bacteria and archaea,NMDS analysis based on Bray-Curtis distance and ANOSIM test,the community division of FL and PA is reasonable.Temperature,electrical conductivity,total organic carbon,ammonia nitrogen,nitrate nitrogen and total nitrogen had strong correlation with bacterial community,while the total organic carbon and ammonia nitrogen had significant effects on archaeal community.(2)Xukou Bay and Zhushan Bay were selected to analyze the mechanism of microbial community as typical sites.Zero-sum model analysis showed that the community structure of bacteria and archaea in Xukou Bay was mainly affected by deterministic processes,while both stochastic processes and deterministic processes shaped the bacterial and archaeal communities in Zhushan Bay.Generally speaking,in the microbial communities of the two life styles,the contributions of ecological processes to the community composition were listed in the following order: homogeneous selection,dispersal limitation,undominated fraction,homogenizing dispersal.