| Ocean, a great ecosystem on earth, is a physical organization of diverse of microbes. Therefore, microbial community composition and dynamics play an important role in sustainability of marine ecosystem and can be an indicator of its inhabiting environment. In this paper, molecular techniques were employed to investigate the spatial and temporal variability of the benthic bacterial communities in Jiaozhou Bay, north China, and the vertical distribution of bacterial and archaeal communities along discrete layers of a deep-sea cold sediment sample at the East Pacific Rise (EPR) (~13oN). The results indicated that the microbial community composition and structure in the two sediment ecosystems were both closely related to environmental factors and therefore could be an indicator of the whole ecosystem. In addition, some results also provided evidence that some microbes might play an important role in biogeochemical cycles in these environments.Sediment samples were taken at 8 stations for four seasons from Jiaozhou Bay. Total genomic DNA was extracted from each of the samples and 16S rDNA clone libraries were constructed to investigate the composition and spatial and temporal variability of bacterial communities. The benthic bacterial communities in the sediment of Jiaozhou Bay displayed a diversified composition, including members from 13 bacterial phylum and some unclassified sequences (28%).α-,β-,γ-,δ- proteobacteria, Chloroflexi, Firmicutes, Bacteroidetes, Actinobacteria and Cyanobacteria were the dominant groups and members of Acidobacteria, Planctomycetes , Verrucomicrobia, Gemmatimonadetes, Chlorobi, Fusobacteria and Deinococcus-Thermus were also found in sediment of Jiaozhou Bay. Total community structure exhibited a clear seasonal succession whereas spatial variations were also detected in response to the environmental settings such as total nitrogen and total phosphor content. Comparative phylogenetic analysis of the closest relatives of the sequences obtained in Jiaozhou Bay revealed the presence of influences of human activities such as the influence of harbor, aquaculture and heavy metal contamination, which exhibited spatial and temporal specificities. For example, there were obvious harbor influence at station C4 and D6, whereas A3 and Y1 were more related to fresh water and oil contamination.16S rDNA based DGGE and clone libraries were used to study the bacterial communities and archaeal communities in the deep-sea cold sediment sample collected at the EPR (~13oN), respectively. Results revealed that both bacterial and archaeal communities displayed a clearly stratified distribution along four discrete layers, which were greatly affected by the vertical zonation of geochemical features. The high percentage of hydrothermal-related members existing in prokaryotic communities (34.7% of the bacterial sequences and 31% of the archaeal sequences) suggested the considerable impact of the hydrothermalism on the surrounding environments, whereas total community analysis indicated this area was a transitional region from the hydrothermal vents to the cold sediment with great biological and ecological importance.Comparison of the dominant bacterial groups inhabited both Jiaozhou Bay and the EPR revealed a considerable difference in phylogeny and the source environments of their closest relatives, indicating the great impact of the total environmental settings of a ecosystem to the microbial community. Therefore, microbial community structure, especially the dominant microbial groups, could be a good indicator of certain ecosystem. The results of the work also indicated that both human activity and the natural environmental factors are forging the composition and function of microbial community. Furthermore, this paper described some useful information for further studies such as the geochemical cycles and global climate change by providing a baseline of the microbial community in the sedimentary environments of Jiaozhou Bay and the EPR (~13oN).
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