Studies On Microbial Community Structure In Typical Sea Areas And Their Biogeochemical Implications

Microbes, as main executors of various biogenic element transformations,play critical roles in regulating global biogeochemical cycles and environmentalremediation. Exploring microbial diversity, their biogeographic distribution patternsand their response to environmental changes allow to gain insight into understandingbiogeochemical processes. Interplay between microbes is another important aspect inmicrobial ecology study, but previous efforts have focused mainly on single orcomplex microbial assemblages where microbial interactions were neglected. In theface of complex microbial communities, it is of great interest to determine theinherent interactions between various taxa inhabiting in a specific niche. Thetaxonomic relatedness determined functional interaction could help to ascertain thecoupling of various biogeochemical processes. In this study, microbial diversity of theChinese marginal seas, including Pearl River Estuary (PRE), Bohai Sea (BS), NorthYellow Sea (NYS), South Yellow Sea (SYS) and the north East China Sea (NECS),and South Pacific Gyres (SPG) were investigated. The various factors that havesignificant effects on the microbial distributions were further analyzed. In addition,the co-existing patterns of microbes inhabiting in sediments of the Chinese marginalseas were explored which will provide new information regarding the interaction ofvarious biogeochemical cycles in the coastal sediment.The aquatic and benthic microbial community compositions of PRE, a typicalsubtropical estuary of China, are largely unknown. The microbial assemblages alonghorizontal and vertical gradients of PRE were analyzed using454-pyrosequencing andflow cytometry. The abundance of heterotrophic bacteria displayed a decreasing trendtowards saltwater areas. Nutrients were determinant factors in driving the distributionof heterotrophic bacteria while the abundance of Synechococcus was negativelyrelated to turbidity. Both bacterial and archaeal community dendrograms partitionedthe samples into three groups, i.e., whole water column of freshwater sites, surface water of saltwater sites and bottom water of saltwater sites. In freshwater sites,Betaproteobacteria and MG-I (Marine Group I, Thaumarchaeota) were abundant,with no significant differences between water layers. In saltwater sites,Synechococcus (Cyanobacteria) and SAR11(Alphaproteobacteria) dominated thesurface and bottom waters, respectively. Phylogenetic shifts of MG-II (Marine GroupII, Euryarchaeota) in different water layers were also observed. In addition, a newsubgroup of MG-I was designated in the present study, i.e., MG-I. Salinity, nutrientsand dissolved oxygen explained most of the microbial community variations. Thehigh nutrient inputs to freshwater area of PRE have shifted the bacterial communitiestowards copiotrophic groups, especially Sphingomonadales, resulting a substantialdistinct community composition from other estuaries. Dissolved oxygen explainedmost of the microbial variations of freshwater sites. While Methylophilales ofBetaproteobacteria was positively correlated to dissolved oxygen, Rhodocyclales wasnegatively correlated. Two subgroups of MG-I (MG-I II-1and MG-I II) wereabundant in freshwater sites and dissolved oxygen was the most significant factorgoverning their distributions. Both benthic bacterial and archaeal communities infreshwater samples were also clearly distinct from those in saltwater samples. Inaddition, vertical stratifications of bacterial community but not archaeal communitywere observed at saltwater sediments, in contrast to the consistency of microbialassemblages at different depths of freshwater sediments. The microbial biomarkers offreshwater and saltwater samples were clearly different. The abundance ofDeltaproteobacteria and MG-I were higher in saltwater sediment whereas Choloflexi,Spirochaetes, Betaproteobacteria and methanogens were more prevalent in freshwatersediment. Spatial distance was found to be more important in governing microbialcommunity structures than environmental factors.Microbial communities of the Chinese marginal seas have rarely been reported.Here, the bacterial and archaeal community structures and abundance of surfacesediments from4sea areas including BS, NYS, SYS and NECS were surveyed by16S rRNA gene pyrosequencing and quantitative PCR. The results showed that the4geographic areas harbored distinct microbial communities from each other at OTU level, whereas the microbial communities of BS, NYS and SYS were more similar toeach other than to NECS at higher taxonomic level. Gammaproteobacteria, MG-I andDHVEG-6(Deep Sea Hydrothermal Vent Group6) were predominant in BS, NYSand SYS while Deltaproteobacteria, MCG (Miscellaneous Crenarchaeotic Group)and MGBD (Marine Benthic Group D) were prevalent in NECS. Spatial distance alsoexplained most of the variations in microbial compositions of the north Chinesemarginal seas, which might result from that BS, NYS, SYS and NECS havingdifferent sediment sources. Temperature and dissolved oxygen of bottom water weresignificant in determining both bacterial and archaeal communities whereaschlorophyll a in sediment was significant only in structuring archaeal community. Inaddition, Bacteria was numerically dominant relative to Archaea across all samples.While Bacteria showed a decreased trend towards NECS, Archaea was elevated inNECS.Based on the benthic microbial composition data described above, the co-existingpatterns between sediment microbes in the Chinese marginal seas were analyzed.Using network analysis, strong positive correlations were observed betweensulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB), and betweenSRB and nitrite-oxidizing bacteria (NOB), indicating the interaction of intra-sulfurcycle processes and the coupling of sulfur and nitrogen cycles. Relationships betweenarchaeal clades uncovered strong and wide correlations between MCG and othergroups suggesting a center role of MCG in coastal benthic environment. Inversely,MG-I displayed negative correlations with other clades, which might indicate thelifestyles of heterotrophic and autotrophic clades were mutually exclusive.The sediment microbial community structure of SPG, a representative ofoligotrophic environments, was investigated. The stratified microbial profiles instation U1371located just south of SPG were analyzed. Both bacterial and archaealcommunities displayed a clear shift along with sediment depth. Dissolved inorganiccarbon explained most of the bacterial variations in sediment of SPG. Choloflexi andPlanctomycetes were prevalent in the surface sediment of SPG, whereasGammaproteobacteria and Deltaproteobacteria dominated the coastal sediment. These results indicated that bacterial assemblages and their impact factors betweenoligotrophic and eutrophic sediments were significantly different from each other.A detailed outline of microbial community sturctures of the Chinese coastal seas(including BS, NYS, SYS, NECS and PRE) and SPG, and the environmental factorsthat influence the microbial assemblages were described in the present study, whichwill be of great value to understand the global microbial distribution patterns.Moreover, the co-existing patterns of microorgainsms inhabitated in the Chinesecoastal seas were explored in this study which allow to gain insight into the couplingof various biogeochemical processes.