Bacterial Community Structure Of Cyanobacterial Water In Freshwater Ponds

The rapid development of intensive farming in recent years has lead to severe pollution in ponds with frequent blooms of Cyanobacterial. These blooms adversely impact the development of aquaculture. Studies have found connections between the Cyanobacterial bloom and the bacterial population. However, existing research mostly focused on the bacterial population of Cyanobacterial blooms in lakes and reservoirs, whereas little information is available for ponds. Studying the bacterial community structure in the Cyanobacterial bloom ponds is important for understanding the bloom mechanism, as well as monitoring and remedying the wellbeing of the farming water bodies.The current study examined freshwater ponds from four farms in three regions(i.e., Guangdong, Yunnan, Guizhou) which with Cyanobacterial blooming, along with the reference ponds that was free of such bloom. The physical, chemical and biological factors were measured, and PCR-DGGE and high-throughput sequencing were applied to determine the bacterial community structure at the time of the blooms. In addition, by the Cyanobacterial bloom tracking simulation experiment and by the high-throughput sequencing technology we determined the dynamics of the bacterial community structure bacterial population throughout the Cyanobacterial bloom cycle. Henceforth, a theoretical basis was established by more thoroughly understanding the mechanism of the formation and development of the Cyanobacterial bloom in freshwater farming ponds, which paves way for the future measures to rectify the bloom problems. The main results are listed as follows:1.Correlation between Cyanobacterial bloom and the physical and chemical factors of the waterIt was found that the soluble phosphates(PO4-P) content was significantly higher in Cyanobacterial blooming pond than that in the control pond(P<0.01). Linear regression analysis revealed a positive correlation between PO4-P and chlorophyll a(Chl.a), which represents the degree of Cyanobacterial blooming(R2=0.869, P<0.01).2.Bacterial community structure in freshwater farming ponds during Cyanobacterial bloomingAll of the Cyanobacterial bloom was incurred by Microcystis in the four studied farms. In the phylum level, the percentage of Cyanobacteria and Bacteroidetes was higher in the Cyanobacterial blooming pond than in the control pond. In contrast, the percentage of Actinobacteria was lower in the Cyanobacterial blooming pond than in the control pond. In the gene level, the percentage of Pseudanabaena, Flexibacter, Cytophaga and Flavobacterium was higher in the Cyanobacterial blooming pond than in the control pond. In contrast, the percentage of Synechococcus, Candidatus Microthrix and Acidimicrobium was lower in the Cyanobacterial blooming pond than in the control pond.The difference in the bacterial population diversity is relatively small between the blooming ponds and the reference ponds in same farm, whereas such difference in bacterial diversity is large between ponds which in different farms. The bacterial community structure is similar between the blooming ponds and the reference ponds in the same farm, but the bacterial community structure has large differences between ponds which in different farms.3.The dynamics of the microbial community structure in the aquaculture water during Cyanobacterial bloomThe dynamics of the bacterial community during the evolution of the Cyanobacterial bloom was simulated with the aid of high-throughput sequencing. It was found that the bloom was incurred by Microcystis. The percentage of Bacteroides increased along with the escalation of the Cyanobacteria bloom and declined when the bloom diminished. In contrast,the percentage of Actinobacteria declined constantly throughout the life cycle of the bloom. At the end stage of the bloom, dissolved oxygen was almost depleted in the water, and the anaerobic Heliobacteria of the Firmicutes phylum thus gained a high percentage in the overall bacterial population. The bacterial diversity of the ponds decreased with intensifying bloom and recovered as the bloom faded away.