自养型氨氧化古菌Marine Group I（MGI）是海洋中最重要的氨氧化微生物，往往在寡营养海域占据优势。申请人的前期研究发现，MGI也可大量存在于富营养的近海沉积物，并形成独立的进化分支，衍生出特殊的异养代谢潜能。目前近海底栖生境中MGI的生态型分化和有机质代谢特征高度不明，阻碍了对其驱动的元素循环过程的认知。本项目拟以我国东部边缘海为代表，通过零模型和系统发生分析，揭示MGI在近海底栖生境中的群落构建机制及生态型分化特征，鉴定近海沉积物MGI的新类群；获得近海底栖MGI的富集/纯培养物，通过底物利用、基因转录和酶学分析，阐明其代谢有机质的过程与机制；同时，结合培养过程中的氨氧化速率及有机质代谢基因和氨氧化基因在培养和原位环境的表达水平，探讨近海底栖MGI降解有机质与其氧化氨间的耦合关系。本研究将提升对MGI物种多样性及生态学功能的认知，深化对近海底栖微生物驱动的元素循环过程的理解。

As autotrophic ammonia-oxidizing archaea, marine group I (MGI) are the most important ammonia oxidizers in the marine environment and often dominate the oligotrophic marine system. Our preliminary results showed that MGI were also abundant in the eutrophic coastal sediments, forming a separate evolutionary cluster with unique heterotrophic metabolic capacity. However, the ecotype differentiation and organic matter metabolic property of MGI that inhabit the coastal sediments are largely unknown, hindering our understanding of their roles in biogeochemical cycling. In this proposal, null model analysis will be performed to reveal the community assembly mechanism of MGI in coastal environments, with the sediment of the eastern Chinese marginal seas as representatives. Their ecotype differentiation will also be investigated to identify novel MGI clusters. The enrichment and/or isolate of coastal benthic MGI will be obtained; then, examination of substrate consumption, gene transcription and enzymatic activity will be performed to reveal their organic matter utilization process and mechanism. Meanwhile, measurement of ammonia oxidation rate, and expression of organic matter utilization gene and amoA gene during incubation and in natural sediments will be performed to reveal the coupling of organic matter utilization and ammonia oxidation driven by coastal benthic MGI. This study will enhance our understanding of the species diversity and ecological role of MGI and provide insights into the microbially-driven biogeochemical processes in coastal sediments.