深海偏顶蛤-化能合成菌共生体系的协同演化和互作机制研究

深海偏顶蛤是深海化能生态系统主要的优势物种，其鳃上皮细胞共生有数以千计的化能合成细菌，是热液冷泉次级生产力的主要来源。无共生的贻贝从近海向深海化能生态系统的迁移中，逐渐与化能细菌建立内共生，是贻贝成功占据热液冷泉生态位的关键事件。内共生建立后，深海偏顶蛤与内共生菌的严格对应关系是宿主与共生菌交互反馈的结果，其机制有待认知。本项目在已有11种深海偏顶蛤样品和6种深海偏顶蛤基因组数据基础上，补充进化节点的外共生型贻贝（Idas sp.）数据，分别开展宿主和共生菌的比较基因组研究，寻找与共生菌内共生密切相关的基因簇，揭示内共生体系的适应性进化特征和遗传基础。通过高空间分辨率的转录组、代谢组研究，揭示含菌细胞独特的基因表达模式和代谢状态；开展深海原位去共生、共生复染和交叉侵染实验，分析共生互作动态过程中的细胞学响应和分子调控网络，揭示深海偏顶蛤内共生的互作机制，为深海特殊生命过程提供新认知。

With thousands of chemosynthetic bacteria dwelling in their gills, mussels belonging to the family Bathymodiolinae dominate communities in cold seeps and hydrothermal vents. The symbionts can fix carbon through the oxidations of methane and sulfide to support the host mussels, and even the regional ecosystems. Intracellular symbionts were acquired in several independent lineages, leading to the successful colonization of Bathymodiolines in deep-sea vents and seeps. To understand the evolution of endosymbiosis in the group, in addition to six genomes of Bathymodiolines with intracellular symbionts, we will sequence genomes of Idas mussels, which possess only extracellular symbionts on their gills. Comparative genomic analysis will shed light on the genetic basis of the adaptive features linked to endosymbiosis. Endosymbiotic specificity was found to be a common phenomenon in Bathymodiolines. Regulations of symbiotic specificity involve the exchange of signaling molecules and cross-talking of many genes between host and symbionts. We will compare expressional profiles of bacteriocytes and other cells by tissue-specific transcriptome comparisons, single-cell transcriptome analysis using 10x genomics as well as spatial transcriptomics to unveil special metabolic and physiological progresses in cells with symbionts. Last but not least, deep-sea in-situ symbiont-loss, symbiont-reacquirement and cross-infection experiments following the in-situ sample fixations will be carried out to study multi-omics responses of the partners during their initial contacts and biofilm forming, establishments of endocytosis, endosymbiosis and the final symbiotic equilibrium. The new findings of the projects will reveal the genetic and molecular mechanisms underlying symbiotic specificity in the Bathymodiolus-Gammaproteobacteria interactions, which will provide new insights into the special life process and adaptive evolution of organisms in deep-sea extreme environment.