太湖微囊藻主型的优势确立、特征及其与环境因子的关系研究

Cyanobacterial blooms have become the major environmental problem in the lake waters. Studying the dynamic of the blooms and its relationship with the environmental factors is crucial to elucidating the mechanisms for massive occurrence of the blooms. Since the correlation between the cyanobacterial genotypes and the environmental factor provide a novel clue to elucidate the driving forces for forming water blooms, the study on Microcystis genotypes and their seasonal evolution, by DNA sequencing technologies, has been becoming a new research direction. The present project will target on Taihu Lake, the typical eutrophic lake in China, to study the basic characteristics and the dynamic patterns on the morphotypic and genotypic diversity of Microcystis and their relationship with the environmental factors (such as water temperature, pH, DO, turbidity, TN, NH3-N, NO3-N, TP and PO4-P ) of Lake Taihu. At different phases during the development of blooms, samples will be collected and examined through the microscope and sequencing technology in the typical regions of the lake. Meanwhile, the ITS gene database will be also constructed. The responses of Microcystis morphotypes /genotypes to the related environmental factors were physiologically and molecularly explored. Isolation of Microcystis strains will be performed using the Micropipet method followed by continuous washing, then obtained strains will be subsequently sequenced for ITS regions. The dominant genotypes and strains will be identified comparing the strains' sequences with highly frequent sequences from the field samples. Using the dominant strains/genotypes to study their physiological characters under different environmental conditions (temperature, disturbance and turbidity), it is expected that significant advantageous points of the dominant Microcystis genotypes will be demonstrated, therefore the inner-driving mechanism of Microcystis blooms in Lake Taihu at the molecule level can be eclucidated in some extent, which may provide the scientific basis for the further prevention and control of water blooms.

蓝藻水华是湖泊水体中的一大环境问题，对水华动态及其与环境因子关系研究是揭示水华暴发、发展机制的重要基础。蓝藻基因型与环境因子的关系研究为水华发生的驱动机制揭示提供了新的思路，借助基因测序技术，微囊藻水华的基因型构成特征及演化成为新兴的研究方向。本研究拟以典型富营养化湖泊-太湖为例，在前期研究基础上，通过显微观察和基因克隆文库构建研究水华不同时期微囊藻形态型和基因型在典型湖区的分布特征，分析其时空变化规律，揭示优势基因型，探讨其与环境因子（水温、pH、DO、浊度、总氮、氨氮、硝态氮、总磷及正磷酸盐）的相关关系，揭示其响应机制；同时，利用单藻株分离技术拟筛选出太湖微囊藻优势基因型藻株，模拟研究该类型藻株在水华暴发前期和优势维持期对水温、扰动、浊度等的响应关系，探讨优势基因型获得竞争优势的内在机制和驱动因子，从分子水平揭示太湖水华动态发展的内部驱动机制并为水华防控管理措施的提出提供理论依据。

水华动态及其与环境因子关系研究是揭示水华暴发、发展机制的重要基础，基因测序技术为微囊藻水华的基因型构成特征及演化提供新的研究方向。本研究完成了该项目的各项任务，达到了预期目标，完成研究论文3篇并已在相关国际期刊发表，主要表现在以下方面：（1）形态型演替特征在典型湖区表现为由冬春季的水华微囊藻、鱼害微囊藻和片状微囊藻向夏秋季的铜绿微囊藻和惠氏微囊藻演替的过程，但在全年的动态组成上，水华微囊藻和鱼害微囊藻在西部和南部湖区的比例构成相对稳定，在夏秋季的比例构成高于北部湖湾区，尤其是水华微囊藻，成为太湖全年的优势形态型微囊藻。（2）获得2460条有效的微囊藻ITS序列，可以划分成677个ITS基因型（genotype）。表明太湖微囊藻的基因多样性非常丰富，连续出现在2个点位或在同一个点位连续出现2次以上的基因型仅有83个，表明太湖每个点位之间和月份更迭期间都有大量的基因型的转换。（3）基因型监测发现太湖优势基因型微囊藻为A型基因型微囊藻，A基因型在太湖西部湖区和南部湖区有稳定的优势地位，南部湖区A包含的序列数占南部总序列数的周年平均比例为38.2%，西部湖区相对最高达41.1%，而湖湾区的平均比例为26.1%，表明具有强水动力特征的开敞水域有利于A基因型的优势维持。（4）单藻株研究显示单一形态型可以同时包含多种基因型，但不同基因型微囊藻的变异度在相同形态型内部低于不同形态型之间，表明微囊藻的形态型与基因型分类分化上仍具有一定同源性。（5）单藻株研究发现A基因型微囊藻的形态型归属到水华微囊藻，生理测定进一步发现该A型微囊藻较其他蓝藻（微囊藻和鱼腥藻）具更快低温恢复能力和更快的比生长速率。综合野外和实验室数据，表明水华微囊藻（即以A基因型微囊藻为代表）在次年的水华恢复生长和暴发时期可以在微囊藻种群中迅速生长并形成优势形态型与基因型，在为野外水华初期恢复生长起到关键性作用，并在整个水华期间维持该优势地位。本项目的研究结果将为深入揭示蓝藻基因型与环境因子关系的水华发生驱动机制提供新思路，为水华的深层认识与有效防控提供重要的信息。