Microbial Community Structure In Specific Ecological Processes In The Yellow Sea And East China Sea, China

Study of microbial diversity at community level is essential for understanding the distribution and function of microbes in the ocean ecosystem. In order to better understand relationship between microbes and environmental factors, especially response of microbes on specific ecological processes, we studied Microbial community structure in several specific ecological processes in the Yellow Sea and East China Sea by molecular methods (denaturing gradient gel electrophoresis and 16S rDNA clone libraries).To better understand response of bacterial community structure on phytoplankton bloom, we firstly investigated bacterial community composition during the spring phytoplankton blooms in the central Yellow Sea. In the cruise of 2007, we focus on bacterial community structures associated with phytoplankton bloom. Statistical and phylogenetic analysis applied to the two molecular methods both revealed differences in bacterial community composition between bloom station and post-bloom station as well as two bloom stages (bloom- and decay-) at bloom station. At phylum level, bacterial communities at bloom station were dominated by Alphaproteobacteria, Cytophaga-Flavobacteria-Bacteroides (CFB) and Gammaproteobacteria, whereas Alphaproteobacteria and Gammaproteobacteria were dominant members at post-bloom station. At order level, no obvious predominant subgroups were found at post-bloom station. In contrast, predominant subgroups were observed in bloom samples and they changed over the course of the bloom. Rhodobacterales (mainly Roseobacter) and Flavobacteriales (mainly Flavobacterium) were the predominant subgroups in the bloom period whereas Roseobacter became the unique predominant subgroup in the decay-bloom period. From a biogeographic point of view, the bloom-associated bacterial communities in the Yellow Sea were similar to those found during bloom conditions in other ocean regions. This suggests that there are specific bacterial taxa widely associated with blooms found in different ocean regions. Together with previous bloom studies, our data indicate that Rhodobacterales and Flavobacteriales as the dominant bloom-associated bacterial clusters are cross-ocean distributed, suggesting that they play important roles in the bloom events.In the cruise of 2009, we focus on temporal and vertical changes of bacterial community diversity and the effects of environmental factors on bacterial community distribution. Clustering of DGGE band patterns showed that temporal variations were observed in two spring phytoplankton bloom stations (St. B20 and St. B23) while vertical variations were only found in samples at St. B20. In addition, we analyzed the effects of environmental factors on bacterial community distribution by canonical correspondence analysis (CCA). The results showed that silicate, salinity and depth affected significantly the bacterial community composition. DNA sequencing revealed that Alphaproteobacteria (41%), Gammaproteobacteria (30%), and CFB (20%) dominated in bacterial groups during spring phytoplankton blooms in the central Yellow Sea.Eutrophication and consequent algal blooms give rise to severe environmental problems in shore environments, but the process and microbiological phenomena concerned are still not clearly known. Here we report the impact of a sudden bloom of Ulva prolifera in Jiaozhou Bay, China on the microbial community during and after it. Bacterial community structure on the surface of U. prolifera thalli and in seawater in an Ulva blooming region in Jiaozhou Bay was investigated by two molecular methods. Statistical analysis on the clone libraries indicated that bacterial community structure presented no significant differences between two algal samples. Thallus-surface bacterial communities identified by 16S rDNA clone library were dominated by Alteromonadales, Flavobacteriales, and Rhodobacterales. Sequences affiliated with Gammaproteobacteria, Alphaproteobacteria and CFB were detected in all the four seawater samples. However, their different distribution frequencies among the four samples and the presence of some specific bacterial clusters in some samples indicated changes in the bacterial community composition over the course of the bloom. The dominant bacterial clades changed from Alteromonadales and Rickettsiales in A-SW, to Flavobacteriales and Alteromonadales in B-SW, to Alteromonadales and Campylobacterales in C-SW, and to Rickettsiales, Rhodobacterales and Flavobacteriales in D-SW. Some specific dominant bacterial assemblages were present in some seawater samples, such as Campylobacterales in C-SW and Actinobacteria in D-SW. Our results gave insight into the changes in the bacterial community composition in seawater in blooming region during the course of macroalgal Ulva bloom, which contributes to understanding the impact of Ulva blooms on microbial communities.Human activities give rise to heavy pressure on coastal ecosystem. In order to understand the impact of human activities on microbial community structure, we studied seasonal changes of bacterial community diversity and the relationship with environmental factors in the Jiaozhou Bay. Results of the richness of DGGE band and Shannon-Wiener diversity index both showed that the highest and the lowest bacterial diversity were observed in samples of August and November, respectively. Clustering analysis of DGGE band pattern showed that samples from four seasons grouped one cluster respectively, indicating bacterial community structure were different among samples from four seasons. DNA sequencing revealed that bacterial groups observed in Jiaozhou Bay were Gammaproteobacteria (40%), Alphaproteobacteria (16%), CFB (16%), Actinobacteria (12%), Actinobacteria (4%), Planctomycetes(4%), Firmicutes (4%) and Unclassified bacteria (4%).CCA results showed that temperature, phosphate and total nitrogen affected significantly the bacterial community composition, which suggested great influence of eutrophication in Jiaozhou Bay on bacterial community structure.Changjiang Estuary is an important interface between terrestrial and marine environments, highly complex and dynamic, and seasonal hypoxia occurring in near-bottom waters. How the archaeal community responds to such changing conditions is very important for the understanding of structure and function of the estuarine ecosystem. Archaeal community and the effects of environmental factors on the microbial community distribution were investigated at five sampling sites in the Changjiang Estuary hypoxia area and the adjacent East China Sea (ECS) in June, August and October, 2006. Clustering analysis of DGGE band patterns revealed that most of samples in October grouped together, which separated from those in June and August. Analysis of DNA sequences revealed that the dominant archaeal groups in the Changjiang Estuary hypoxia area and the adjacent ECS were affiliated to Euryarchaeota (mainly Marine Group II) and Crenarchaeota. CCA results showed that salinity had a significant effect on the archaeal community composition instead of dissolved oxygen. These results provide useful data to further understand distribution and function of archaeal communities in marine ecosystem.From these results, specific microbial community structure was observed in specific ecological processes, suggesting that microbial community made response on specific ecological processes. In addition, environmental factors affected significantly the microbial community composition, and the determinant control factors on microbial distribution pattern were different in specific ecological processes.