冬季太湖表层底泥产毒蓝藻群落结构和种群丰度

The community structure and abundance of microcystin-producing cyanobacteria in surface sediment of Lake Taihu in winter

应用荧光定量PCR对冬季太湖不同湖区底泥表面有毒微囊藻和总微囊藻种群丰度进行调查,同时基于PCR-DGGE技术对底泥中有毒微囊藻群落结构进行分析。结果表明:微囊藻在太湖底泥表面分布广泛,所有采样点都检测到有毒微囊藻存在,且不同湖区有毒微囊藻和总微囊藻种群丰度存在显著差异,有毒微囊藻和微囊藻基因型丰度范围分别为1.23×104—3.75×106拷贝数/g干重和2.56×104—1.07×107拷贝数/g干重,有毒微囊藻与微囊种群丰度的比例为4.8%—35.2%;DGGE指纹图谱显示,冬季太湖不同湖区表层底泥中有毒微囊藻群落结构相似性较高,相似性系数为70.2%—96.0%。虽然不同湖区基因型组成存在差异,但所有样品中占优势的基因型是一致的。同时发现,优势基因型所占的比例与样品的香农多样性指数呈负相关。序列分析表明,mcyA序列长度为291bp,序列相似性超过97%。综合定量PCR结果和底泥中叶绿素a和藻蓝素浓度的测定结果,可以得出2010年冬季太湖蓝藻越冬主要集中在梅梁湾、竺山湾、贡湖湾和湖心。通过建立荧光定量PCR分析方法,为研究湖泊底泥中蓝藻种群丰度动态变化奠定了基础。

Lake Taihu is a large,shallow,eutrophic freshwater lake,which has frequently experienced cyanobacterial bloom in summer in the past decades.In winter,a large quantity of cyanobacterial cells sink on the sediment surface to overwinter.Therefore,it is important to quantify the biomass of cyanobacteria on the sediment to predict the location and the extent of water bloom in summer.However it is difficult to identify and to count cyanobacterial cells in sediment using microscopy method,and microscopic identification cannot differentiate between the toxigenic and non-toxigenic genotypes.In recent years,this problem has been resolved by using molecular techniques such as PCR and quantitative real-time PCR（qPCR） with primers targeting toxin-producing genes.The microcystin gene cluster which contains 10 genes,namely from mcyA to mcyJ has been widely used to reveal microcystin-producing species in genera Anabaena,Microcystis and Planktothrix.Detection of cyanobacteria and their toxin-producing ability using molecular methods has been successfully applied to a diverse range of water and sediment environments.In this study,we use quantitative real time PCR to quantify the abundance of microcystin-producing cyanobacteria and Microcystis,and PCR-denaturing gradient gel electrophoresis technique to investigate the community structure of microcystin-producing cyanobacteria in surface sediment of Lake Taihu in winter.qPCR data showed that Microcystis and microcystin-producing cyanobacteria were present in all of sediment samples and their abundance varied significantly in different lake areas,ranging from 1.23×104copies/g dry weight to 3.75×106copies/g dry weight and from 2.56×104 to 1.07×107 copies/g dry weight,respectively.The proportion of microcystin-producing cyanobacteria to Microcystis ranged from 4.8% to 35.2%.DGGE patterns indicated that the composition of microcystin-producing cyanobacteria were very similar in surface sediments collected from different lake areas,and the similarity values were between 70.2% and 96.0%.Although the composition of genotypes of microcystin-producing cyanobacteria slightly varied among samples,the dominant band is same.The number of dominant band was negatively correlated with Shannon index.Taking into consideration of qPCR analysis and the concentration of Chlorophyll-a and Phycocyanin,we concluded that in the winter of 2010 cyanobacteria of Lake Taihu mainly overwinter in four lake areas,Mei liang bay,Zhu shan bay,Gong hu bay and center part of Lake Taihu.Our results showed that quantitative real time PCR is a feasible method to investigate the dynamics of toxic cyanobacteria in lake sediment.