多糖介导的甲藻--黄杆菌特异性共生及其驱动的碳转化过程研究

甲藻和黄杆菌类群细菌（以下简称黄杆菌）是海洋微食物环的重要组分，是驱动海洋碳循环的重要微型生物。研究表明甲藻和黄杆菌在海洋环境关键的“藻-菌”微界面中的共生具有特异性，但是这种特异性共生产生的机制及两者通过特异性共生驱动的碳转化过程还不清晰。前期研究中，我们发现多糖可能是介导甲藻和黄杆菌特异性共生的桥梁。基于此，本研究拟首先通过分析不同甲藻产生的溶解性有机碳含量及多糖含量和结构，解析多糖对“藻-菌”微界面溶解性有机碳的贡献及其结构差异性，阐明特异性共生的物质基础；然后通过分析黄杆菌的多糖水解酶种类、验证其活性，解析黄杆菌利用多糖的机理，阐明特异性共生的分子机制；最后通过分析多糖转化后碳的赋存形态和含量，揭示特异性共生介导的多糖形式有机碳的转化和归宿。本研究能够揭示海洋环境中多糖介导甲藻-黄杆菌产生特异性共生关系的机制以及两者协同介导的碳转化过程，为解析关键界面的碳循环过程提供科学依据。

Dinoflagellates and flavobacteria are two important organisms intermediating the carbon cycle in marine environment. They interact with each other in Phycosphere which is the key “micro-interface” in marine environment. The specific symbiosis between Dinoflagellates and flavobacteria has been acknowledged, while the mechanism of the specific symbiosis and the carbon cycling process driven by the algal-bacterial symbiosis are far from well-known. In previous studies, we found that polysaccharides could be an important player intermediating the symbiosis between Dinoflagellates and flavobacteria. Based on the new finding, this study aims to 1) reveal the differences of polysaccharides secreted by different Dinoflagellates and their proportions in total dissolved organic carbon by measuring the quantity of secreted polysaccharides and total dissolved organic carbon, and analyzing the molecular structure of polysaccharides; 2) demonstrate the molecular mechanism of polysaccharides utilization of specifically symbiotic flavobacteria by identifying hydrolases secreted by different flavobacteria and detecting the activities of hydrolases; 3) reveal the transformation and incidence of polysaccharides driven by flavobacteria by measuring metabolites in the process of polysaccharides hydrolyzation and speciation of dissolved organic carbon. This study will be helpful for revealing the mechanism of specific symbiosis between Dinoflagellates and flavobacteria intermediated by polysaccharides, and demonstrating the carbon cycling driven by the algal-bacterial symbiosis.