Succession Of Bacterial Community Structure And Potential Significances Along The Sediment Core Spanning Approximately 20 Megaannum Years In The South China Sea

The deep biosphere harbors a vast ecosystem of bacteria,archaea,and fungi,with some unique biodiversity,and functions on geological time scales.Microbial communities usually change in response to surrounding geochemical conditions.However,deep biosphere studies to date almost always focused on geochemical control of and interactions with microbial communities.Very few studies have addressed the relationship between microbial composition and depth distance or geological age distance.Such relation construction is crucial in determining to what extent the current microbial distributions could reflect deposition history and geological times.The relationships between the microbial communities and the biogeochemical impact,sedimentological properties,and past geological events in subseafloor environments have remained poorly defined.(1)To evaluate the potential impact of geological processes and depositional history on shaping the subsurface biosphere,the bacterial community structures in a sediment core of the South China Sea was investigated by molecular approaches that target 16S rRNA gene fragments.Samples were obtained from different lithologic intervals at site U1433 during the International Ocean Discovery Program(IODP)Expedition 349.Bacterial abundance decreased rapidly with depth,with nearly three orders of magnitude decline within the first 100 m below seafloor(mbsf).Community diversity displayed a similar decreasing pattern,yet,a slight increase in diversity emerged in the early to middle Miocene.Such excursion might reflect enhanced cell activity in response to increasing temperature due to a steep geothermal gradient.Non-metric multidimensional scaling ordination revealed that the bacterial communities along the sediment core represent four clusters based on depth and geological time.There were distinct bacterial community shifts among clusters at 4.50-98.93 mbsf(Pleistocene),108.15-273.20 mbsf(Pleistocene),296.09-709.13 mbsf(Pliocene and late Miocene),and 732.10-789.91 mbsf(early to middle Miocene).Classification analysis revealed a striking pattern:the relative abundance of microorganisms affiliated with Gammaproteobacteria,Actinobacteria,and Cyanobacteria overall consistently decreased with depth,whereas those affiliated with Chloroflexi,candidate division OP9,candidate phylum BHI80-139,and Nitrospirae increased;these findings correspond to different clusters.Total organic carbon content and ratio of total organic carbon:total nitrogen,along with pore water phosphate concentration and salinity,were the statistically most significant variables that explained the bacterial community cluster pattern,which indicates potential linkages of bacterial communities to changes in quality and quantity of buried organic matter over geological time scales.,Geographic isolation across depth was more important than environmental condition and geological age for the development of unique community structure in marine deep biosphere,although environmental variables partially shaped bacterial community composition.(2)Strain JL3085T was isolated from the surface water collected from the South China Sea(16° 49' 4" N,112° 20' 24" E).Based on the results of morphological,physiological and biochemical characteristics,GC content,determination of fatty acids and quinines,and phylogenetic tree analysis,strain JL3085T represents a novel species of the genus Echinicola,for which the name Echinicola rosea sp.nov.is proposed.