南海北部水合物区非甲烷短链烷烃的微生物厌氧降解机制研究

Marine cold seeps are closely related to oil and gas reservoirs, natural gas hydrates and global climate change. In these systems, sediment-associated microbial communities can not only utilize abundant methane, but also degrade non-methane short-chain alkanes. Microbial short-chain alkane degradation is reported to be globally distributed in various marine ecosystems. Geological and geochemical settings indicate that short-chain alkanes are also rich in hydrate-bearing sediments in the South China Sea. Therefore, it can be inferred that non-methane short-chain alkanes in this area are also undergoing microbial anaerobic degradation. However, the degradation mechanism and its influence on the ecosystem are rarely studied so far. Therefore, in this project, the applicant will employ metagenomics combined with metabolomics to investigate microbial communities inhabiting in sediments associated with gas hydrates in the northern South China Sea. Two questions will be answered in this project: (1) who are degrading short-chain alkanes anaerobically and what about the key metabolites? (2) how do these microbial degraders interact with other microorganisms? The results on the degradation of non-methane short-chain alkanes can not only clarify the role of these compounds in biogeochemical cycles, but also provide theoretical foundation for the identification of the gas origin of natural hydrates based on microbial methods.

海底冷泉与油气藏、天然气水合物等资源及全球气候变化密切相关。冷泉沉积物中的微生物不仅能利用含量丰富的甲烷，还可以降解非甲烷短链烷烃。根据非甲烷短链烷烃厌氧降解微生物在世界范围内的广泛存在以及南海水合物区的地质-地球化学背景，可以推断：在南海海区与水合物相关的沉积物中非甲烷短链烷烃同样经历着微生物厌氧降解。然而，该海区有关沉积物中微生物厌氧氧化短链烷烃的机制及其对海底沉积物中生态系统的影响却鲜见报道。本项目拟采用宏基因组学结合代谢组学的方法对南海北部水合物分布区及其附近沉积物中的微生物群落进行分析，确定这些生态系统中厌氧降解短链烷烃的微生物和其代谢通路中的标志产物，并探究短链烷烃厌氧降解微生物与其他微生物之间的相互作用关系。非甲烷短链烷烃的厌氧降解机制的明晰，既可揭示非甲烷短链烷烃在生物地球化学循环中的作用，也可为利用微生物方法鉴定水合物气源的成因提供理论依据。

冷泉微生物介导的厌氧烃降解过程对认识水合物的形成与分解以及全球气候变化都具有重大意义。本项目围绕冷泉厌氧烃降解微生物开展研究，揭示了冷泉浅层和深层沉积物中厌氧烃降解细菌和古菌的多样性、垂向分布、生物地理分布、烃降解机制以及与其他微生物的互作关系。发现广古菌的不同类群以及Asgard古菌Heimdallarchaeia采用烷基辅酶M还原酶激活甲烷和其它短链烷烃的厌氧氧化；来自绿弯菌门、δ-变形菌纲以及Asgard古菌等类群通过富马酸加成反应介导液态烷烃和芳香烃的厌氧降解。在冷泉沉积物生态系统中，这些厌氧烃降解微生物分布于表层沉积物层到硫酸盐被耗尽的深层；生物地理分布表明，除冷泉外，烃降解微生物如绿弯菌门、δ-变形菌纲以及Asgard古菌在全球海洋范围内具有广泛分布。此外，还发现冷泉沉积物病毒可以通过诱导宿主死亡来影响微生物对烃的降解过程；冷泉烷烃降解微生物可以通过生物固氮作用解决氮限制问题。本研究的成果不仅丰富了对微生物介导碳循环的科学认知，同时也为海上石油和天然气勘探提供微生物方面的支撑。