附生CFB菌群的多样性及其对浒苔形态建成诱导作用的研究

The free-floating Ulva prolifera, that formed the Yellow Sea green tides, has remarkable morphological character - denser branching thalli than the attached populations. This feature facilitates the long-time and far-distance drifting of the algae. The epiphytic Cytophaga-Flavobacterium-Bacteroides (CFB) clade is essential to the macroalgae morphogenesis (MG). It is important to analyze the biodiversity of the epiphytic CFB clade and identify the bacterial strain inducing the branching thalli of U. prolifera for understanding the interaction between the algae and the accompanying bacteria and comprehending the formation of the Yellow Sea green tides. In this proposal, we will analyze the 16S rDNA sequences of the CFB bacteria from the epiphytes of the free-floating U. prolifera and attached populations from different place, and study the biodiversity of the CFB clade. Axenic cultures of different U. prolifera will be established; the morphogenetic inducing bacterium strains will be isolated and identified. The relationship between the dense branching of the free-floating U. prolifera and the specific constitution of the CFB bacteria will be judged by co-cultivation of the algae and the isolated bacterium strain. The results will be helpful to analyze the mechanism of the specific morphological character formation of the bloom-forming algae, to discuss the host specificity of the MG bacteria, and provide novel clues to explain the cause of the Yellow Sea green tides and figure out the origin of the bloom-forming algae.

黄海绿潮浒苔（Ulva prolifera）具有分枝密集的显著形态特征，这为其长时间、远距离漂移提供了有利条件，而附生CFB（Cytophaga-Flavobacterium-Bacteroides）菌群在石莼属绿藻的形态建成过程中发挥了重要作用。研究附生CFB菌群对浒苔形态建成的诱导作用和机理，对于深入理解浒苔与其附生菌群的相互作用关系，探讨黄海绿潮形成和暴发的原因均有重要意义。 本项目拟利用特异性引物分别构建黄海绿潮浒苔与不同种群定生浒苔附生CFB菌群的16S rDNA文库，分析其生物多样性；构建不同浒苔种群的无菌材料体系，分离、鉴定对浒苔形态建成有诱导活性的CFB菌株，通过菌与藻的共培养来判断黄海绿潮浒苔密集分枝的形成是否与其附生的特定CFB菌群有关。从而分析绿潮浒苔特殊形态特征形成的原因，并对该类细菌的宿主特异性问题进行探讨，为解释黄海绿潮的暴发原因及绿潮藻的来源提供线索。

黄海绿潮浒苔（U. prolifera）具有分枝密集的显著形态特征，这为其长时间、远距离漂移提供了有利条件，而附生CFB（Cytophaga-Flavobacterium-Bacteroides）菌群在石莼属绿藻的形态建成过程中发挥了重要作用。本项目利用特异性引物分别构建了历年黄海绿潮浒苔与不同种群定生浒苔附生CFB菌群的16S rDNA文库，分析其群落结构，发现漂浮浒苔相比于定生浒苔，附生CFB菌的多样性低，优势类群突出，且有一簇CFB菌在历年的漂浮浒苔中均有出现，而在定生浒苔中没有出现，这对追溯漂浮浒苔的来源有一定的指示意义。建立了联合利用多种抗生素培养浒苔无菌株系的方法，获得了漂浮浒苔和定生浒苔的无菌材料，证明了浒苔在无菌条件下无法正常地分化和发育，附生菌对于浒苔的形态建成具有不可或缺的作用。对漂浮浒苔和定生浒苔的附生菌进行了分离、纯化和鉴定，初步建立起浒苔附生菌的菌种库，并通过菌、藻共培养的实验，对所分离的4株CFB菌对浒苔形态建成的诱导作用进行了验证。本项目证明了附生CFB菌在浒苔假根、分枝分化过程中的重要作用，建立了浒苔无菌材料的培养方法，为进一步深入解析附生菌对浒苔形态建成诱导作用的分子机理、探究在绿潮暴发过程中的菌、藻相互作用关系打下了基础。