南海北部与DMSP降解相关的Roseobacter类群的分子生态学研究

Roseobacter clade is dominated in the marine system, which play important role for the productivity of marine ecosystem and global climate change through dimethylsulfoniopropionate (DMSP) degradation. Although some of the research has focused on the ocean area, it was unclear about its ecological functions and response to DMSP transformation in the marine system, especially in the coastal areas which are rich in DMSP. In this project, DMSP lyase gene (dddP) and DMSP demethylation gene (dmdA) were acted as molecular marker. Combined with clone libraries, high throughput sequencing and quantitative PCR, the study was to assess the roles of Roseobacter clade in DMSP degradation based on the RNA level. Representative region, such as the Pearl River freshwater, Luzon Strait, upwelling zones and area far from the coast, will be focused in the study. By coupling analysis of various environmental factors, it will be clear about Roseobacter clade structure, its number and its metabolic activity in the northern South China Sea. Further, the DMSP degradation mechanism of Roseobacter clade will be verified in the tropical coastal seawater. To study the molecular ecology of Roseobacter clade in the tropical sea, not only provide invaluable data of its ecological functions in coastal waters, but also help us to understand the potential mechanisms of Roseobacter clade in DMSP degradation as well as providing new insight of the important roles in the marine ecosystem.

Roseobacter类群是海洋中占优势的微生物种群，其对DMSP(β-二甲基巯基丙酸内盐)的降解作用对海洋生态系统生产力以及全球气候变化等方面有着重要的作用。但是对于Roseobacter类群在海洋生态系统中的结构及活性规律仍缺乏足够的认识，其在DMSP含量丰富的近海中的生态功能及其响应机制尚不清楚。本项目瞄准这一前沿问题，以Roseobacter类群中DMSP裂解酶基因dddP和去甲基化基因dmdA为分子靶标，从RNA水平出发，结合克隆文库、高通量测序和定量PCR等分子生物学技术，以南海北部典型区域为研究对象，通过耦合分析各种环境因素，明确Roseobacter类群在该区域的群落结构及代谢活性的规律，深入探讨其在热带近海DMSP降解中的作用机制。本项目将为深入了解这一微生物类群在海洋生源硫转化中的作用机制提供科学依据，为进一步揭示其在海洋生态系统中的重要地位和作用提供新的认识。

本项目以南海北部为研究对象，研究南海北部微生物及玫瑰杆菌类群对海洋环境的响应与反馈，揭示玫瑰杆菌类群在热带海域DMSP降解过程中的作用。研究显示，微生物群落结构在水平和垂直梯度存在明显的差异，表层微生物多样性要高于深层，微生物群落同环境因子间存在明显的相关关系。蓝细菌、变形细菌、放线菌和拟杆菌是南海北部优势的微生物种群。研究进一步显示在水平和垂直深度下玫瑰杆菌类群结构和丰度的明显不同，尤其在上升流系统中具有很高的丰度；南海北部玫瑰杆菌类群有其独特的类群分布，显示了明显的生物地理分布特征。通过对DMSP降解功能基因的研究发现，表层海水有着较高的DMSP的去甲基化和裂解酶基因丰度。另外，玫瑰杆菌A/2类群的dmdA基因丰度要高于A/1类群的基因丰度，说明玫瑰杆菌A/2类群在南海DMSP去甲基化过程中起着更为重要的作用。垂直梯度dmdA基因多样性差异明显，浅水层以Marinovum, Ruegeria, Jannaschia和Leisingera属为主，深水层主要以Phaeobacter和Ruegeria为主。除此之外，近岸站位同远海站位也有明显的差别，体现了dmdA基因在空间上的变异性。相关分析表明大多数的环境因子（如温度、盐度、深度、磷酸盐和叶绿素）都与dmdA基因的多样性具有明显的相关关系。与dmdA基因丰度分布类似，表层海水也具有较高丰度的玫瑰杆菌dddP基因，表明DMSP转化为DMS主要发生在表层海水。南海北部不同区域和垂直深度dddP基因的丰度存在明显的差异，说明环境因素对DMSP裂解酶基因起着重要的调节作用。本项目研究玫瑰杆菌类群在热带海域生态分布特征，深入探讨其在热带近海DMSP降解中的作用机制，为进一步揭示其在热带海洋系统中的重要地位和作用提供新的认识。