Light-dependent regulation of coccolithophore host-virus interactions: mechanistic insights and implications for structuring infection in the surface ocean

浮游植物是一种微小的光合藻类，它们构成了海洋食物网的基础，负责生产地球上近一半的氧气，但却占地球生物量的1%。维持高产量与生物量比率的稳定状态意味着，这些生物平均每周生长、死亡和更换一次。病毒的掠夺性感染已成为浮游植物种群高死亡率的主要机制。尽管病毒死亡率在构建海洋微生物生态系统中很重要，但人们对调节宿主-病毒相互作用的基本机制知之甚少。浮游植物天生就依赖于光和光合作用。鉴于对宿主资源的需求，感染这些生物体的病毒也必须从根本上依赖于光和光合作用。本项目将探索光与病毒感染之间的关系，为光如何影响海洋表面的病毒感染和浮游植物死亡建立一个框架。广泛分布的浮游植物物种赫胥黎Emiliania huxleyi及其相关病毒球粒石病毒（Coccolithovirus）已成为研究藻病毒相互作用的重要模型系统，因为它具有生态相关性，并且从许多生理、分子、生化、基因组和实地研究中获得了集体机制的见解。基于实验室的培养研究将用于阐明光在介导赫胥黎氏杆菌感染中的作用，特别是解决病毒感染是否需要光，以及确定病毒可能选择的光调节宿主代谢过程以成功感染和生产。然后，这些观察结果将扩展到自然种群，使用可操作的、基于现场的实验来阐明光在表层海洋结构感染中所起的作用。该项目为罗格斯大学的一名本科生和一名博士后研究员提供了实践培训。为了促进海洋知识普及，研究人员将与教育和公共宣传工作人员以及罗非鱼电影有限责任公司合作，根据研究成果和《下一代科学标准》制作一部教育视频。本视频针对初高中和本科学生，扩展了一个已经成功的视频系列，通过真实的研究调查突出科学实践。它将通过与新泽西州科学教师协会、国家科学教师协会、国家海洋教育者协会和国家生物教师协会的现有联系开放获取和传播。病毒的掠夺性感染是浮游植物群体中观察到的高裂解率的主要机制。作为水生环境中最丰富的生物实体，病毒提供了超过四分之一的光合固定碳，从而为微生物食物网提供燃料，并将碳输出到更高营养水平和深海。尽管它很重要，但病毒引起的死亡率的估计很少包括在净初级生产力和深度碳输出的全球模型中，部分原因是我们缺乏对调节宿主-病毒相互作用的基本因素的机制理解。对于感染专性光自养生物的病毒，光与感染过程之间存在固有的和基本的相互作用，并且依赖于光调节的宿主代谢过程，这可能是病毒复制所必需的。利用模型藻宿主赫胥黎Emiliania huxleyi及其相关的球粒石病毒，该项目解决了以下假设：1)赫胥黎Emiliania huxleyi的感染动力学是通过依赖光的过程驱动的，特别是光介导病毒进入和复制，病毒重定向宿主能量以最大化病毒复制；2)光增加病毒衰变，减轻宿主的病毒压力。这种机械的细胞框架将用于阐明光在自然球石藻种群结构感染中所起的作用，使用可操作的野外实验。鉴于光是海洋最基本、最容易测量的特征之一，这项工作最终将为模拟全球海洋中病毒感染的生物地球化学影响提供一个背景。

Phytoplankton, microscopic photosynthetic algae, form the basis of marine foodwebs and are responsible for producing nearly half the oxygen on the planet, yet represent 1% of Earth's biomass. Steady-state maintenance of a high production to biomass ratio implies that, on average, these organisms grow, die and are replaced once every week. Predatory infection by viruses has emerged as the primary mechanism responsible for the high mortality rates of phytoplankton populations. Despite the importance of viral mortality in structuring marine microbial ecosystems, little is known about the fundamental mechanisms that regulate host-virus interactions. Phytoplankton are inherently dependent on light and photosynthesis. Given the need for host resources, the viruses that infect these organisms must, therefore, also fundamentally depend on light and photosynthesis. This project will explore the relationship between light and viral infection to develop a framework for how light influences viral infection and phytoplankton mortality in the surface ocean. The widespread phytoplankton species Emiliania huxleyi, and its associated virus, Coccolithovirus, has emerged as the prominent model system for investigating algal-viral interactions due to its ecological relevance and collective mechanistic insight from numerous physiological, molecular, biochemical, genomic, and field studies. Laboratory-based culture studies will be used to elucidate the role light plays in mediating infection in E. huxleyi, specifically addressing whether light is required for viral infection as well as identifying the light-regulated host metabolic processes that viruses may co-opt for successful infection and production. These observations will then be extended to natural populations using manipulative, field-based experiments to elucidate the role light plays in structuring infection in the surface ocean. This project provides hands-on training for a Rutgers University undergraduate student, as well as a postdoctoral researcher. To facilitate ocean literacy, researchers will work with the Education and Public Outreach staff and Tilapia Film, LLC to develop an educational video based on research findings and the Next Generation Science Standards. This video, aimed at middle, high school, and undergraduate students, expands on an already successful video series that highlights scientific practices through real research investigations. It will be open access and disseminated through existing connections to the New Jersey Science Teacher Association, the National Science Teachers Association, the National Marine Educators Association, and the National Biology Teachers Association. Predatory infection by viruses is the primary mechanism responsible for the high lysis rates observed in phytoplankton populations. As the most abundant biological entities in aquatic environments, viruses turn over more than a quarter of the photosynthetically-fixed carbon, thereby fueling microbial foodwebs and short-circuiting carbon export to higher trophic levels and the deep sea. Despite its importance, estimates of viral-induced mortality are rarely included in global models of net primary productivity and deep carbon export, in part because we lack a mechanistic understanding of the fundamental factors that regulate host-virus interactions. For viruses infecting obligate photoautotrophs, there is an inherent and fundamental interaction between light and the infection process, as well as a dependence on light-regulated host metabolic processes that may be required for viral replication. Using the model algal host, Emiliania huxleyi and its associated Coccolithovirus, this project addresses the hypotheses that: 1) infection dynamics in E. huxleyi are driven through light-dependent processes, specifically that light mediates viral entry and replication, and that viruses redirect host energy to maximize viral replication, and 2) light increases viral decay relieving hosts of viral pressure. This mechanistic, cellular framework will then be used to elucidate the role light plays in structuring infection in natural coccolithophore populations using manipulative field-based experiments. Given that light is one of the most fundamental, readily, and easily measured features of the ocean, this work will ultimately provide a context for modeling the biogeochemical impact of viral infection in the global ocean.