Studies On Diversity, Spatial-temporal Distribution And Toxin Of Bloom-forming Cyanobacteria In Poyang Lake

Eutrophication of lakes and its subsequent formation of cyanobacteria bloomsare the major global environmental issues, and these problems are becoming moreand more serious, due to the global economic development and human activities.The massive occurrence of cyanobacterial blooms not only seriously damages theecosystem balance of the water body, but also affects the ecological functions ofthese waters due to the cyanobacterial toxins and odor of secondary metabolites,posing a major threat for public safety. In recent years cyanobacteria blooms havehappened in Chinese large lakes, including Taihu and Dianchi Lakes. Poyang Lake,the largest freshwater lake in China with water area as5000km2during the rainyseason and watershed area accounting for more than90%the land area of theprovince, is important wetlands reserve and A-level protected areas for migratorybirds in the world. Based on the fat that the Poyang lake has been under theaggravation in water quality in recent years, the cyanobacterial blooms and theirtoxin production were studied in this study, and these studies were expected to givescientific supports for the evaluation of the lake ecosystem and environment,warning of cyanobacterial blooms and further removal of these blooms and theirrisks. The main results were shown as followings:The full year investigation during2011to2012identified20species of waterbloom forming cyanobacteria belonging to seven genera, with the dominace ofMicrocystis and Anabaena genera accounting for75%of the total number of bloomforming species. Molecular detection showed that the annual average abundance ofcyanobacteria is equivalent to8.08×10716rRNA gene copies/L, with the highestnumber in July, reaching1.26×108copies/L, and the maximum cyanobacterialabundance was found at the south site1#as5.84×108copies/L. Overall the southarea of Poyang Lake has a relatively higher cyanobacterial abundance. Nine Microcystis species were identified in the Poyang Lake as following:Microcystis aeruginosa, Microcystis wesenbergii, Microcystis novacekii, Microcystisviridis, Microcystis smithii, Microcystis ichthyoblabe, Microcystis flos-aquae,Microcystis pseudofilamentosa, Microcystis botrys. The molecular phylogenetic treebased on16S and ITS gene sequences presented a high diversity of Microcystisspecies. The average abundance of Microcystis in whole lake is molecularly detectedas6.00×105copies/L, with main distribution at0#~7#sites in the south. The highestseason was found in October with the average abundance as1.08×106, and the peakabundance found at4#site as9.28×106copies/L.The toxic Microcystis cells were mainly distributed in the south. The annualaverage abundance of the toxic Microcystis, as detected in mcy gene copy number, is7.49×104copies/L. The maximum abundance of toxic Microcystis reached up to1.32×105copies/L in April, especially5#site with the highest abundance is1.2×106copies/L. The toxin production of the toxic Microcystis strains isolated fromthis lake showed that the Microcystis strains containing mcyA gene had differentamount of microcystin production. The highest microcystin production within thestrains reached4.69mg/g dry weight.Correlation analysis among the cyanobacterial and Microcystis abundnaceswith environmental factors showed that water eutrophication in the Poyang lake ishigh, and variation in cyanobacteria and Microcystis indicated that turbidity was afactor to negatively influence the abundance of cyanobacteria and Microcystis,reflecting the critical roles of water turbidity in governing the cyanobacteriallcommunity in the Poyang lake.