Microbial Community Structure And Its Relationship With Environmental Variations In Typical Areas Of The Yellow Sea And East China Sea

Marine microorganisms have the characteristics of high abundance and widedistribution. The microorganisms can produce many active substances and playimportant roles either in the energy flows or in the material circulations. Study onmarine microorganisms is a hotspot in marine ecology. In this article, the microbialcommunity structure and special bacteria in typical areas of the Yellow Sea and EastChina Sea were studied by sequencing, molecular biological methods and culture.In order to study the annual variation of bacterial community structure in thecentral Yellow Sea, PCR-DGGE, clone and sequencing methods were employed.There were eight main classes of bacteria in the sampling area, includingAlphaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Cyanobacteria,Actinobacteria, Flavobacteria, Bacilli and SAR406cluster. Alphaproteobacteria wasthe dominant class in the central Yellow Sea, Gammaproteobacteria, Flavobacteriaand Bacilli were also the common classes in different months. Quantity of bands inDGGE profiles showed the diversity of different samples. In this study, diversity washighest in September with25bands while October was the lowst with19bands. Thecluster analysis which based on the presence and absence of each band showed anannual variation of bacterial community structure. Structures of different layers’samples in different months were alike and could be clustered together duringJannuary to May, while the structures were much more complex in June to Novenber.The hydrogeological environments （temperature and salinity） might influence thecommunity structure most. For example, the Yellow Sea Cold Water Mass influencedthe bacterial community structure in June to Novenber significantly, especially inAugust, which samples could be clustered in an independent branch.Bacterial community structures in one section of the East China Sea in May2011 were studied by Roche454pyrosequencing technology.17seawater samples and5sediment samples were collected in5stations. Totally,149067optimized reads withthe average length of454nt in V1-V3regions of the16S rDNA were obtained. Thediversity was high （the average of Shannon indices was5.38）, and the sedimentsamples （7.65） were higher than seawater ones （4.71）. In all,22phyla,34classes,74orders,146families, and333genera were identified by comparing against the SILVAdatabase. More than10phyla were reported in the East China Sea for the first time.There was some unclassified information in each taxonomic category with theproportions increased from “phylum” to “genus”. The unclassified information washigher in sediment samples （8.07-71.61%） than in seawater samples （1.52-59.96%）.Alphaproteobacteria, Gammaproteobacteria, Deltaproteobacteria; and Flavobacteriawere some dominant classes in seawater samples while Gammaproteobacteria,Deltaproteobacteria, and Phycisphaerae were dominant in sediment. Comparation ofclustering and partition of water masses showed that bacterial diversity andcommunity structure might be affected by the water masses in the East China Seaand other factors. The samples in Kuroshio surface water （KSW） and intermediatewater （KIW） were clustered together, samples in Changjiang diluted water （CDW）and Kuroshio subsurface water （KSSW） might be influenced by chlorophyllfluorescence. There were also some comprehensive factors which could influencethe bacterial community structure.Archael community structure in the same area in the ECS were studied also byRoche454pyrosequencing technology and obtained196018optimized reads inV3-V5regions of16S rDNA.171653optimized reads were detected with theaverage length of495nt in seawater samples while sediment samples contained24365optimized reads with the average length of511nt. The diversity was high （theaverage of Shannon indices was4.79）, and the sediment samples （6.25） were higherthan seawater ones （4.36）. Totally,2phyla,13classes,10orders,21families, and25genera were identified by comparing against the SILVA database. Unclassifiedinformation in each taxonomic category with the proportions increased from“phylum” to “genus”. The unclassified information in sediment （1.40-86.95%） was more than it in seawater （0.04-85.25%）. Marine Group I and Thermoplasmata weredominant in seawater while Marine Group I, Thermoplasmata Halobacteria, GroupC3and Marine Benthic Group B were dominant in sediment. The comparation ofrichness indices and partition of water masses showed that the indices from high tolow were samples in KSSW （average Chao1indices was2751）, KIW （2432）, KSW（2259）, CDW （2131） and shelf mixing water （SMW,1843）. The high proportions ofunclassified information in bacterial and archaeal studies indicated that the ECScontained a lot of unknown microbial resources.Jiaozhou Bay is a semi-enclosed bay and can be affected by human activitiessignificantly. The abundance of coliform bacteria is an indicator of environmentalquanlity. We can either obtain the results on the temporal and spatial scales orappraise the environment by monitoring the abundance. The MPN method wasemployed to study the abundance of coliform bacteria in Jiaozhou Bay. A9-year（108months） monitoring result showed clear annual variations. The abundance ofcoliform bacteria increased in summer and autumn and reduced in winter and spring.The maximum (in Semptember,（2.18±1.93）×10⁴·L^-1) was about2.1times of theminimum (in April,（1.05±0.71）×10⁴·L^-1) on an annual basis. The abundance ofcoliform bacteria in the surface seawater in Jiaozhou Bay was different in4marinedivisions （the estuary area, the inner bay area, the outer bay area and the bay moutharea）. It’s highest in estuary area (（5.20±2.35）×10⁴·L^-1) and lowest in inner bay area(（0.41±0.08）×10⁴·L^-1), the highest value was about13times of the lowest one.Correlation analysis between the abundance of the coliform bacteria and theenvironmental factors showed that the abundance was significantly corre-lated withsewage discharged in Qingdao, salinity, concentration of total nitrogen, dissolvedorganic carbon, and chlorophyll-a in the Jiaozhou Bay. Analysis on the interannualvariations showed that the abundance of coliform bacteria declined from2005to2009, suggesting that the environmental quality of Jiaozhou Bay had been improved.The pollutin was much more serious in the estuary area and bay mouth area whichindicated those areas should be paid more attention on environmental protection inthe future. The researches on microbial community structure and special bacteria in typicalareas of the Yellow Sea and East China Sea helpe people to better understand therelationship between environmental changes and microorganisms. It can also layfoundation for researches on microorganisms in the Yellow Sea and East China Sea.