微囊藻群体胶鞘附生细菌群落结构和功能及其对微囊藻表型的影响

Microcystis spp. are dominant species in cyanobacterial bloom. In field, Microcystis cells are surrounded by mucilage composed of polysaccharide and exist in colony form, one of the most important characteristics for their dominance and different phenotypes. Microcystis colonies exist in different size and morphology, and are often colonized by numerous and complex bacteria. Specific interactions between Microcystis and their attached bacteria were assumed to be very important for metabolism of polysaccharide and development of Microcystis bloom. However, functions of the attached bacteria in the mucilage of Microcystis colonies and their effect on the Microcystis phenotypes are still unclear. In this project, we conducted field investigation and laboratory experiment to explore community structure and gene expression pattern of bacteria associated with Microcystis colonies during Microcystis bloom using 16S rDNA high-throughput sequencing and metatranscriptome. These methods are new molecular methods developed recently and very effective in studying complex microbial communities in a habitat as a whole. Shift of community structure and functional diversity of Microcystis and bacteria in Microcystis colonies collected in different month and their relevance with environmental factors were analyzed to reveal ecological roles of bacterial communities during different phases of the cyanobacterial bloom. Community structure and gene expression patterns of bacteria communities associated with different Microcystis phenotypes were compared to reveal potential effect of bacteria on the phenotype of Microcystis colonies. Bioinformatics analysis was with emphasis on metabolic network of polysaccharide in order to reveal the contribution of Microcystis and their attached bacteria on the synthesis and degradation of polysaccharide. Thus we can deduce the effect of bacteria in the mucilage on Microcystis phenotypes and their ecological roles in the deveplopment of cyanobacterial blooms. This study will throw new light on mechanisms of microbial interactions in cyanobacterial bloom forming lakes, and be helpful for elucidating their ecological role in cycling of organic carbon in eutrophic lakes.

群体胶鞘是微囊藻具有不同表型、形成水华、维持优势的重要因素之一。胶鞘中富集的大量细菌，和微囊藻之间形成了独特的藻菌关系，在胶鞘多糖代谢及水华生消过程中起着重要作用。然而，目前对微囊藻群体胶鞘中附生细菌的功能及其对微囊藻表型的影响并不清楚。因此，本项目拟针对太湖微囊藻水华不同发展阶段及不同表型的微囊藻群体，结合野外调查和室内模拟实验，借助16S rDNA高通量测序和宏转录组学技术两种方法，从整体上研究微囊藻群体胶鞘小生境中藻与附生菌的群落结构和功能基因表达水平变化；揭示不同表型藻群体中附生菌在群落组成及代谢活动中的差异；重点比较分析不同表型藻群体中多糖降解相关的基因表达差异及其来源菌群，从而揭示附生菌对微囊藻表型的影响及其在微囊藻水华发展中的生态作用。本项目的开展有助于深入认识微生物之间的相互作用在微囊藻水华发展过程中的作用及其机制，对富营养化湖泊有机碳循环过程研究有重要的参考意义。

群体胶鞘是微囊藻具有不同表型、形成水华、维持优势的重要因素之一。胶鞘中富集的大量细菌，和微囊藻之间形成了独特的藻菌关系，在胶鞘多糖代谢及水华生消过程中起着重要作用。本项目通过在太湖梅梁湾每月一次采样以及室内模拟实验，探讨了不同表型微囊藻群体藻与附生菌的群落结构及基因表达差异。16S rDNA高通量测序结果表明，蓝藻大群体（120µm）附生菌多样性低，群落组成相对稳定，以变形菌和拟杆菌为主,蓝藻组成显著影响附生菌的组成。基于MG-RAST的宏转录组测序结果分析表明，对于蓝藻大群体，7月9月一组（高水华期）／2月3月一组（非水华期）／以及其他月份（低水华期）等三组。其中蓝藻相关基因的表达在非水华期要多于低水华期，低水华期多于高水华期，拟杆菌与蓝藻类似，变形菌相关基因高表达的数量在低水华期要多于高水华期，高水华期多于非水华期。蓝藻的基因表达显著影响了附生细菌的基因表达，而变形菌和厚壁菌显著影响了蓝藻的基因表达。蓝藻大群体与小颗粒中蓝藻表达的基因明显聚为不同的两类，且在蓝藻大群体中高表达的基因数量低于在小颗粒中高表达基因的数量。表明了蓝藻在小颗粒中代谢活性更高，而在大群体可能已经进入了稳定状态。然而，通过室内同株系的群体和单细胞微囊藻的基因表达模式对比研究，揭示了群体中的高表达基因数量多于单细胞中，表现出了与野外相反的趋势。此外，通过室内模拟温度下降再上升过程中，研究了微囊藻、鱼腥藻的基因表达差异，结果表明，温度下降导致光合作用相关基因相对表达量的下降，但是微囊藻与鱼腥藻的基因表达模式对温度的响应不同。另外，对胶鞘多糖的相关基因的分析，结果表明，变形菌参与了胶鞘多糖的相关代谢，不同形态微囊藻中藻和菌的胶鞘多糖中的基因表达量存在显著差异，因此，藻以及细菌的共同作用可能导致了微囊藻的不同形态。本研究揭示了蓝藻水华不同阶段不同蓝藻的基因表达模式不同以及细菌起到的重要生态作用，为蓝藻水华机理研究提供新思路。