长江口聚球藻-病毒相互作用的时空变化及调控机制研究

Picocyanobacteria, such as Synechococcus are important primary producers in marine environment. Through lysing the host, cyanophages play important roles in regulating the population size, diversity, and redirecting the metabolism of picocyanobacteria, attributable to which, picocyanobacteria-cyanophage interactions are of ecologically important, and influence the biogeochemical cycling in the marine environment. Estuarine environment usually contains unique and diverse population of Synechococcus and its phage due to the environmental heterogeneity. Up to date, ecological studies on Synechcoccus-phage interaction in the estuary have been scarcely reported. In this proposal, studies on molecular ecological investigation and host-phage model system in Changjiang Estuary-East China Sea will be carried out to explore the spatial and temporal variation of Synechococcus-phage interaction and its influencing environmental parameters. Physiological characteristics during phage-host interaction including infection mode (lysogeny/lytic), host range, latent period and burst size will be determined along with investigations on genomes of the typical cyanophage and Synechcoccus and the community structure. Based on studies above, mechanisms of Synechococcus phages adapted to the environment will be illustrated, and more evidences will be provided for the evaluation of ecological roles and biogeochemical significance of virus in the estuary.

超微型蓝细菌（如聚球藻）是海洋初级生产力的重要贡献者。通过侵染和裂解宿主，病毒调控着海洋聚球藻的丰度、多样性、群落结构和代谢途径。因此，聚球藻-病毒相互作用具有重要的生态意义，进而影响海洋生物地球化学循环。河口具有明显的时空异质性和独特的聚球藻及其病毒类群，但目前以二者相互作用为切入点的生态学研究还十分有限。本项目以长江口-东海为研究区域，结合现场分子生态学调查和典型模式体系研究，通过对侵染方式（溶源性/裂解性）、宿主范围、侵染周期、裂解量等病毒-宿主相互作用的生理生态过程的研究，结合典型病毒和聚球藻的基因组分析和群落结构分析，解析长江口区域聚球藻-病毒相互作用的时空变化规律及其环境影响因素，阐释河口区域聚球藻病毒的环境适应机制，为全面评估河口病毒的生态效应和生物地球化学意义提供科学依据。

本研究发现长江口-东海区域存在着极为多样化的的聚球藻及其病毒类群。水体透光率、温度和NH4+是影响聚球藻丰度的重要因素。在冬夏季发现和分离培养出11个聚球藻分支，与地理距离相距甚远的切萨匹克湾十分相近，暗示着蓝细菌广泛存在的扩散作用，而温度、盐度是聚球藻群落的重要选择压力。长江口-东海区域聚球藻病毒分离株多为肌尾和长尾形态，至少可划分为7个类群。冬季聚球藻病毒分离株均为肌尾形态，长尾病毒仅在夏季分离出，且在特定聚球藻分支十分盛行。冬季聚球藻-病毒裂解性发生率较低、裂解周期长、裂解量低、病毒宿主范围广。夏季聚球藻-病毒裂解性侵染率高、专一性强、裂解期更短。因此聚球藻病毒在夏季对宿主群落变动及物质循环的影响更为显著。病毒在特定类型的辅助代谢基因组成、tRNA数量和调节性毒粒蛋白组成的差异可能是病毒适应河口复杂多变环境的重要机制。本研究中，聚球藻-病毒相互作用特点的时空差异分析对全面评估河口聚球藻-病毒相互作用的生态效应和生物地球化学意义十分重要。