Cyanobacterial Community And Diversity In Dongzhen Reservoir, A Drinking Water Reservoir In Fujian Province

Currently, most freshwater resources worldwide are facing eutrophication, a typical characteristic of which is the frequent occurrence of cyanobacterial bloom. In China, cyanobacterial blooms also occur very often each year in many drinking water reservoirs. Some of these cyanobacteria are harmful cyanotoxin-producing algae, which can not only destroy the integrity and balance of healthy aquatic ecosystems, but can also threaten public health. Therefore, it is quite necessary to set up effective strategies for prevention and treatment of cyanobacterial blooms in freshwater lakes and reservoirs. However, understanding the cyanobacterial community structure and diversity, as well as their dynamic changes in the temporal and spatial scales, is a prerequisite to prevention and control of algae blooms. As a drinking water reservoir for Putian city, Fujian Province, Dongzhen reservoir has a potential risk of cyanobacterial bloom in several recent years, due to increasing human activities and deteriorating water quality.Therefore, in this study Dongzhen reservoir was chosen as an example to investigate the cyanobacterial community and diversity as well as the dynamic changes in microbial populations on the time and space scales, by using molecular biology approaches(such as denaturing gradient gel electrophoresis, clone library, 454 pyrosequencing, etc.). Furthermore, multivariate data analysis was employed to examine the relevance between cyanobacterial community and environmental parameters. Meanwhile, two clone libraries, constructed with two different DNA polymerases, Q5 high-fidelity DNA polymerase and exTaq polymerase, were compared to analyze the differences in their capability to reflect the real cyanobacterial community structure and diversity. Finally, the structure and diversity of the total microbial community, in a water column of Dongzhen reservoir in summer was investigated using high throughput DNA sequencing of the bacterial 16 s rDNA. The main findings of this study were summarized as follows:Firstly, a higher variation of cyanobacterial community structure was found in the time scale versus the space scale. In other words, the cyanobacterial community varied significantly in the four seasons during the whole year, while there was no remarkable variation at different depth of the water column in the same season.Secondly, principal components analysis revealed that the distribution in the space scale was influenced by physical environmental parameters of the water,as well as the concentrations of nitrate N and P; The seasonal dynamic variation was mainly influenced by the concentration of organic mass and total nitrogen. Redundance analysis showed a remarkable correlation between temperature, N, P, and the cyanobacterial community structure. Hence, controlling the excessive input of N and P compounds is likely an important strategy for the prevention of the occurrence of cyanobacterial bloom.Thirdly, investigation of the cyanobacterial community structure and diversity within different water layers in four seasons demonstrated that the diversity of cyanobacteria in spring and winter was higher than summer and autumn. FamilyII-GpIIa was the most dominant cyanobacterial family in spring; thereafter it was replaced by familyI-GpI in summer and autumn, although the abundance of familyI-GpI had a decreasing trend. Whereas, in winter, FamilyII-GpIIa again returned to its zenith. The succession of the dominant cyanobacterial lineage was Synechococcus—Cylindrospermopsis—Cylindrospermopsis—Synechococcus/ Chroococcus. In addition, comparative analysis of the two cyanobacterial clone libraries constructed by using Q5 high-fidelity DNA polymerase and exTaq polymerase separately did not show a significant difference. But a little higher community diversity could be found when using Q5 high-fidelity DNA polymerase.Finally, investigation of the microbial community structure and diversity in a water column of summer by using 454 pyrosequencing of 16 s rDNA revealed remarkable differences at different water depth. It was showed that in more deep water layers the bacterial community had higher diversity and more complicated composition. The dominant bacterial phyla in the water column were Actinobacteria, Bacteroidetes, Proteobacteria, Verrucomicrobia, and Cyanobacteria. Among them, the relative abundance of cyanobacteria in different water depths were in the following order: DZ2(1m)>DZ3(10m)> DZ1(0m)>DZ4(26m). The spatial heterogeneity of bacterial community was closely related with the environmental factors and the released organic matter from algae during their growth and apoptosis.