What is the role of cyanophage-encoded auxiliary metabolic genes in the virocell?

聚球藻属和原绿球藻属的海洋蓝细菌是世界海洋中最丰富的原核光养生物。这些蓝细菌受到病毒感染的高度挑战，高达40%的细菌群体被细菌感染。在海洋环境中，噬藻体对生态学、进化和生物地球化学过程具有重要影响。它们参与营养循环，宿主种群控制，并作为基因转移和生态位适应的载体。细菌被噬菌体感染后，宿主细胞转化为所谓的病毒细胞，其中病毒和宿主基因组平行表达。受感染的宿主细胞不再分裂，其唯一的功能是产生病毒体以繁殖噬菌体基因。在这种状态下，诱导不同宿主代谢途径的显著变化。噬藻体还通过引入通常与光合作用和捕光相关的辅助代谢基因（AMG）来补充所需的代谢需求，从而扩展病毒细胞代谢。需要对AMG编码蛋白的生化特征有基本的了解，以阐明最佳病毒复制周期所必需的病毒策略。噬菌体编码的AMG与捕光和色素生物合成相关的生物化学表征表明，它们通常编码高效的酶，这些酶与其宿主对应物有很大不同，可能使病毒细胞代谢重新定向。在该优先计划中，将研究AMG编码蛋白在病毒细胞中的作用、它们与宿主代谢蛋白的相互作用以及它们的可分配性。具体地，将探索在代表水柱中不同深度的蓝光和绿色光下，由噬藻体Syn 9和S-SSM 7攻击的聚球藻属物种WH 8109的病毒细胞。使用质谱为基础的蛋白质组学的宿主噬菌体蛋白质的比例，重点是那些与捕光和色素的生物合成将被确定。这两种策略都旨在深入了解AMG在感染过程中的作用以及它们如何塑造病毒细胞代谢。噬菌体基因组的遗传操作将提供对AMG对病毒体复制的基本性质的更好理解。此外，将在宿主和病毒细胞中评估与光合作用相关的生理参数（光饱和点、O2释放、pH值）以及生态参数，如营养释放（蛋白质、糖原、磷酸盐）。最后，鉴于在蛋白质生物化学方面的强大专业知识，将在分子水平上研究选定的AMG及其与宿主对应物的生化功能。总的来说，该项目将增加关于噬藻体在调节海洋光合作用和营养循环中的作用的全球知识基础。

Marine Cyanobacteria of the genera Synechococcales and Prochlorococcales are the most abundant prokaryotic phototrophs in the world’s ocean. These Cyanobacteria are highly challenged by viral infection with up to 40 % of the bacterial population being infected by phages. In the marine environment, cyanophages have significant impact on ecology, evolution and biogeochemical processes. They are involved in nutrient recycling, host population control and serve as vehicles for gene transfer and niche adaptation. Infection of a bacterium by a phage transforms the host cell into a so-called virocell where both viral and host genomes are expressed in parallel. The infected host cell can no longer divide, its sole function being to produce virions to propagate phage genes. In this state, significant changes in diverse host metabolic pathways are induced. Cyanophages furthermore expand the virocell metabolism by introducing auxiliary metabolic genes (AMGs) often related to photosynthesis and light-harvesting to supplement the required metabolic demand. A fundamental understanding of the biochemical characteristics of the AMG encoded proteins is required to elucidate the viral strategies that are essential for an optimal viral replication cycle. Biochemical characterization of phage encoded AMGs related to light-harvesting and pigment biosynthesis indicate that they often encode highly efficient enzymes that can differ considerably from their host counterparts, likely enabling the redirection of the virocell metabolism. Within this priority program, the role of AMG encoded proteins in the virocell, their interaction with host metabolic proteins as well as their dispensability will be investigated. Specifically, the virocell of Synechococcus sp. WH8109 challenged by the cyanophages Syn9 and S-SSM7 under blue and green light representing different depths in the water column, will be explored. Using mass spectrometry-based proteomics the ratio of host to phage proteins with emphasis on those related to light-harvesting and pigment biosynthesis will be determined. Both strategies aim at gaining insight into the role of AMGs during infection and how they shape the virocell metabolism. Genetic manipulation of the phage genome will provide a better understanding of the essential nature of AMGs on virion replication. Additionally, physiological parameters related to photosynthesis (light saturation points, O2 release, pH), as well as ecological parameters such as nutrient release (protein, glycogen, phosphates), will be assessed in host and virocells. Finally, given the strong expertise in protein biochemistry, selected AMGs will be investigated on the molecular level and their biochemical functions compared to that of the host counterpart. Overall, this project will add to the global knowledge base on the role of cyanophages in regulating oceanic photosynthesis and nutrient cycling.