病毒介导的宿主细胞裂解对元素生物地球化学循环（尤其是碳循环）具有重要意义。在水圈环境中，存在着多样性极为丰富的古菌病毒，但对其裂解宿主细胞机制的研究很少。近期研究表明，多种形态的古菌病毒均通过在宿主细胞表面形成金字塔状结构（VAP）实现宿主细胞的裂解。据此，本项目提出假说：古菌病毒中广泛存在基于VAP的宿主细胞裂解系统，VAP的打开由蛋白单体间互作模式的改变所触发，古菌病毒通过这种裂解方式参与微生物群落结构的调节并推动有机碳的释放。本项目拟以硫化叶菌椭球形病毒SEV1与杆状病毒SIRV2的病毒-宿主系统为模式，综合利用生物化学、成像技术、遗传学及组学等手段，解析古菌病毒感染宿主后VAP的组装与打开等步骤的调控机制，进而通过元病毒组学和单细胞测序技术等方法，了解这一宿主裂解系统的系统发育学和生态学分布。本项目的实施将有助于拓展对热泉等水圈环境中古菌病毒推动碳元素生物地球化学循环新机制的认识。

Cell lysis by viruses releases highly labile cellular components, both organic matters and inorganic nutrients, drastically affecting the biogeochemical cycles, especially the carbon cycle on Earth. Viral metagenomics in extreme environments have revealed a vast diversity of archaeal viruses, suggesting their potentially critical roles in regulating the microbial community and promoting organic carbon release. Recent studies show that several species of archaeal viruses with totally different morphologies, i.e. Sulfolobus ellipsoid virus 1, Sulfolobus islandicus rod-shaped virus 2, Sulfolobus turreted icosahedral virus 1 and a putative Pyrobaculum virus, all induce host cell lysis by forming a virus-associated pyramids (VAPs) on cell surface. Therefore, in this project, we hypothesize that the VAP-based cell lysis system is widely employed by archaeal viruses to regulate the microbial community and mediate the release of organic carbon from host cells. This project entails the analysis of molecular mechanisms underlying VAP assembly and opening during the infection of two Sulfolobus strains, i.e. Sulfolobus sp. A20 and S. islandicus LAL14/1, by their respective viruses SEV1 and SIRV2, by employing biochemical, genetic, imaging technologies and omics approaches. To understand the phylogenetic distribution and evolution of the VAP-based host lysis system, a survey of viruses encoding a homologue of a VAP-specific protein will also be conducted by using metagenomic and single-cell genomic techniques. The execution of the project will improve our understanding of the novel mechanism of archaeal viruses in mediating host cell lysis and their roles in promoting organic carbon release in hydrosphere, especially in extreme environments.