蓝藻拟柱孢藻两形态型（直型和卷曲型）动态演替机制的研究

With eutrophication aggravated in lakes and reservoirs and global warming, cyanobacterial populations have become a trend to form dominant blooms. Recently, environmental rRNA gene cloning libraries have been widely applied to discuss genotype diversity and variations of some cyanobacterial populations, thereby helping us further understand spatiotemporal dynamics and succession strategies of cyanobacterial blooms, and also find dominant ecotypes. A number of studies have been conducted to discuss the genetic diversity and the genotypic composition on the unicellular cyanobacterium Microcystis, but little have been performed on filamentous cyanobacterium. Recently, in many Chinese freshwater bodies, Cylindrospemopsis populations have been found as a new dominant cyanobacterium, furthermore, they could produce various kinds of toxins and thus present a potential threat to drinking-water safety of the public. The genus Cylindrospemopsis possesses multiple phenotypes (straight and coiled), which differed in community succession strategies in water columns. Based on results obtained from previous studies of mine, coiled trichomes of several coiled Cylindrospemopsis strains could transform into straight trichomes and this is a irreversible process. The results provide research foundation and direction for this study. This study will discuss the genetic diversity and the genotypic composition during Cylindrospemopsis blooms, combined with community succession strategies in water columns of two Cylindrospemopsis phenotypes, further understanding dynamic succession processes of Cylindrospemopsis blooms and finding places where blooms first happen, thereby allowing us to predict and control their occurrence, and meanwhile it will further discover and explicitly understand bloom processes of cyanobacteria.

随着湖库富营养化和全球温度升高，以蓝藻类群为优势的水华已成为一种趋势。近年来常常运用构建环境样品rRNA基因克隆文库研究蓝藻水华种群基因型变化，以深入解析蓝藻水华时空演替规律、繁殖策略以及寻找优势生态型。单细胞蓝藻微囊藻基因型组成及分子多样性已进行深入研究，但有关丝状蓝藻相关研究较少。在我国许多淡水水体相继发现拟柱胞藻已成为一种新的蓝藻优势且可产生多种毒素，威胁人类饮水健康安全。此类群具有多形态型（直型和卷曲型），且在水层的动态演替规律不一致。基于以往研究结果，数株卷曲拟柱孢藻藻株卷曲型藻丝可转变为直型藻丝，且是一不可逆过程。此结论为本研究提供了研究基础和方向指导。本研究将探索拟柱孢藻水华期间基因型组成和分子多样性，结合两形态型于不同水层种群演替规律，深入解析拟柱孢藻水华演替过程并寻找水华种源，进而为拟柱孢藻水华监控和治理提供理论基础和指导，同时，也有助于进一步探究和全面掌握蓝藻水华过程。

近年来，我国湖库相继暴发拟柱孢藻水华，威胁公众饮水健康安全。拟柱孢藻是一种温度依赖性蓝藻，全球温度升高趋势下，拟柱孢藻水华进一步扩张。因此，探究拟柱孢藻繁殖及水华机理，深入解析拟柱孢藻水华演替过程并寻找水华种源，可为拟柱孢藻水华监控和治理提供理论基础和指导。本研究基于中国湖库浮游植物大范围调查，分离纯化拟柱孢藻藻株，开展拟柱孢藻弯形、直形两形态藻丝生长竞争实验，基于转录组分析寻找拟柱孢藻不同形态藻丝形态转变基因，最后从基因型多样性层面探究拟柱孢藻水华湖泊拟柱孢藻水华机理。主要结论如下：（1）拟柱孢藻藻丝形态是可逆的，非稳定的形态特征，不适宜作为蓝藻分类学界定物种的形态特征；（2）弯形、直形拟柱孢藻藻丝等比例培养下，氮相对于磷是拟柱孢藻生长限制因子，不同氮浓度、磷浓度、温度条件组合下，直形藻丝丰度是弯形藻丝的1-4倍，表现一定的竞争优势；弯形、直形藻丝以倍数比例培养下，直形藻丝：弯形藻丝混合培养比例由10倍至100倍，直形藻丝竞争优势逐渐减弱，而弯形藻丝：直形藻丝混合培养比例由10倍至100倍，弯形藻丝竞争优势逐渐增强，表明直形藻丝在较低浓度下表现较强的竞争优势；（3）弯形拟柱孢藻藻丝可转变为直形形态，且是不可逆过程；两株不同弯形形态藻株弯形、直形藻丝纯培养物转录组分析发现相同形态藻丝转录组相似度高，确定5个可能与拟柱孢藻藻丝形态调控的基因；（4）拟柱孢藻表现丰富的基因型多样性，研究湖泊发现1008个基因型，不同月份、水深存在一主基因型和较大比例共有基因型，表明拟柱孢藻基因型具有传递性；网络分析表明，拟柱孢藻基因型间表现强相关性，未发现负相关性，低丰度基因型为基石基因型，表明基因型间合作维持群落稳定性，低丰度基因型一旦消失，拟柱孢藻群落稳定性破坏。本研究为拟柱孢藻水华防控提供了理论基础和研究方向。