Diversity And Distribution Of Microorganism In Changjiang Estuarv And Adiacent Areas

The Changjiang River (historically called the Yangtze River) is the third-largest river in the world, with a huge water discharge of9.28x1011m3per year, equivalent to84.4%of the total riverine discharge of the East China Sea. The Changjiang estuary, which is located offshore from the mouth of the Changjiang River, is an area where freshwater, Changjiang Diluted Water (CDW), is mixed with the Taiwan Warm Current (TWC) from the south and Yellow Sea Coastal Water (YSCW) from the north. Because it is the interface of land, freshwater and marine environments, this region is extremely complicated and dynamic. Bacteria, producer and decomposer, plays an important role in marine ecosystem and are recognized as important agents in biogeochemical processes in the earth. In this thesis, we aimed to study distribution and diversity of marine bacteria in the Changjiang Estuary and adjacent areas.Firstly, we studied temporal and spatial distribution of bacteria and virus in the Changjiang estuary and adjacent areas. Bacteria abundance in seawater showed a clearly seasonal variability, with an order of spring> autumn> summer> winter for average bacteria abundance. Horizontal distributions were different in the four seasons. In spring and autumn, bacteria abundance was low in river mouth and coastal areas but higher in offshore areas. In summer, bacteria abundance were higher in north and south areas, but lower in central part, furthermore, there was a large low abundance areas in bottom in south of31°N. In winter, bacteria abundance were higher in east of Zhoushan Islands. Vertical distribution were similar in spring, autumn and winter, that bacteria abundance in all depth(surface,10m, bottom) were quite similar, however, in summer, bacteria abundance decreased with depth which indicated a strong stratification. Virus abundance also had a seasonally variability, despite which were not the same in different depth. There were two opposite horizontal distribution styles for virus abundance, in spring and autumn, virus abundance were lower in river mouth and coastal areas but higher in offshore, while in summer and winter, virus abundance were higher in river mouth and coastal areas but lower in offshore. A positive relationship was found between salinity and bacteria abundance in spring and autumn, but no obvious correlation between other environmental factors (eg. temperature, dissolved oxygen, nutrients) and bacteria abundance were found. Furthermore, virus abundance showed a significant positive relationship with bacteria abundance. The order of sedimentary heterobacteria abundance in the four seasons was autumn> spring> summer> winter. In spring and winter, sedimentary heterobacteria abundance was higher in coastal areas, while in summer and autumn, it was higher in offshore areas. Concentration of organic matter and substrate of sediment could be the two main factors influencing distribution of sedimentary heterobacteria abundance.Secondly, diversity of bacteria in the Changjiang estuary and adjacent areas sediment were studied. Phylogenetic analyses were performed on the prokaryotic community and diversity based on the16S rRNA, bacterial phyla detected included the Proteobacteria, Acidobacteria, Firmicutes, Actinobacteria, Bacteroidetes, Planctomycetes, Nitrospirae, Chloroflexi, Verrucomicrobia, Deinococcus-Thermus, Thermotogae. Proteobacteria was the dominant group in study area. However, community structure was quite different in all three kinds of sediment environments. Most clones obtained from the inlet of the Changjiang river related to uncultured bacteria from terrestrial and freshwater environment, clones obtained from East China Sea shelf related to uncultured bacteria from marine environment. Site in river mouth showed a higher diversity than the other two sites and a more compatible environment resource including both marine and terrestrial16S rRNA sequences.Finally, a systematic study had been conducted on the taxonomy of two strains isolated from coastal sediment of Zhejiang province in accordance with the principle of polyphasic taxonomy. The results showed that both the two strains were gram-negative and non-motile, they showed different cell form in different culture conditions. The predominant cellular fatty acids are iso-C15:0, iso-C17:1ω9c, iso-C17:0, iso-C11:0.3-OH, C16:0, iso-C11:0and C18:1ω7c for strain Y215T and iso-C15:0, iso-C11:03-OH, iso-C17:1ω9c, iso-C11:0and iso-C17:0for strain Y226T. The G+C content was54mol%and56.7%, respectively. The DNA-DNA relatedness between the two strains and type strains were significantly lower than that accepted as the phylogenetic definition of a species. On the basis of their distinct taxonomic characteristics, the two isolated strains represent two novel species of the genus Microbulbifer, for which the names Microbulbifer marinus sp. nov. and Microbulbifer yueqingensis sp. nov. are proposed. The type strains are Y215T (=CGMCC1.10657T=JCM17211T) and Y226T (=CGMCC1.10658T=JCM17212T), respectively.