Role of Latent Virus Infection in Marine Phytoplankton

现在，感染海洋浮游植物的大量病毒是众所周知的。很多工作都集中在阐明病毒裂解的生物学意义(即杀死宿主细胞)及其对广泛的全球过程的影响，而病毒感染的另一个重要方面，潜伏期，在很大程度上被忽视了。尽管20世纪70年代的证据表明浮游植物携带潜在感染，但这一点仍然存在。在潜伏期，病毒稳定地保持在宿主细胞内：它的基因组与宿主的基因组一起复制，并传递给后代细胞。潜伏期的关键方面是病毒可以被重新激活(通常是由环境触发)，杀死宿主并释放新的感染性颗粒。潜伏期在横向基因转移和进化中有意义，并可能赋予受感染细胞优势(例如，对其他病毒的抵抗力)。潜伏期可能代表了病毒在调节海洋浮游植物动态方面的最重要作用。潜伏病毒重新激活的最有可能的触发因素是温度升高和/或紫外线照射，因此，海洋浮游植物的潜伏时间不仅是海洋生态系统的重要组成部分，而且应该在气候变化模型中加以考虑。该项目将检验两个假设：1)潜伏的浮游植物病毒在海洋系统中高度多样化、丰富和普遍；2)海洋温度上升是病毒诱导的关键触发因素。该项目将通过使用基于聚合酶链式反应的方法和电子显微镜对浮游植物(养殖采集和野外样本)进行潜在感染筛查来解决这些假设。一些样本将被诱导(使用高温或紫外线照射来“开启”病毒)，并将通过流式细胞仪检测病毒颗粒。然后，PI将使用病毒分类、全病毒基因组扩增和序列分析的变革性方法来设计诊断探针，以评估环境中的潜伏期。这项研究的更广泛影响将主要来自直接参与研究的科学家与学生/公众之间的互动。例如，这个项目的研究结果将在一个非正式的“科学咖啡馆”项目中讨论，该项目旨在与公众分享最新的科学思想。PI将在非正式开放日期间向K-12学生传授病毒的结构和使用纸板模型进行分子探测的原理。PIS还将进一步将“数量级”(病毒DNA)纳入凯勒-毕格罗实验室数量级(Bloom)计划，旨在向缅因州各地的高中生传授海洋生态系统的功能。Bloom的成果包括了解调查方法，拓宽和加强学生对科学的兴趣。PI与当地学校有联系，他们走访了学龄前到3岁的儿童，向他们传授浮游植物和病毒的知识，并在实验室接待了一名高中工作经验的学生，这名学生帮助从海洋孵化场分离和鉴定病毒。在这个项目的过程中，PI将接待本科生实习生，并将通过我们的合作者与研究生互动。这项研究的主要成果将是关于海洋浮游植物中病毒潜伏期的信息，目前几乎一无所知。浮游植物及其病毒是全球碳循环中的重要组成部分。该项目的发现将进一步了解这些重要的病毒及其传播和生存策略。这些病毒的基因组序列信息将鼓励生物技术公司的参与，这些公司正在积极寻找海洋环境中的新酶、化合物和过程。此外，由于该项目中研究的一些藻类宿主(虫黄藻)是珊瑚共生体，这一发现也将与珊瑚生物学相关，特别是与理解珊瑚漂白有关，珊瑚漂白是由于虫黄藻的丧失而导致的，并被认为与气温上升有关。世界珊瑚礁的命运是广大公众非常关心和关切的。

The great abundance of viruses infecting marine phytoplankton is now well known. Much effort has been focused on elucidating the biological significance of viral lysis (i.e. killing of the host cell), and its effects on wide ranging global processes, while another important aspect of viral infection, latency, has been largely ignored. This is despite evidence from the 1970s indicating phytoplankton carry latent infections. In latency, the virus is stably maintained within the host cell: its genome replicating along with that of the host, and being passed on to progeny cells. The crucial aspect of latency is that the virus can be reactivated (usually by an environmental trigger), killing the host and releasing new infective particles. Latency has implications in lateral gene transfer and hence evolution and may confer advantages to infected cells (e.g. resistance to other viruses). Latency could represent the most important role of viruses in regulating phytoplankton dynamics in the ocean. The most likely triggers for reactivation of latent viruses are increased temperature and / or UV irradiation, hence latency in marine phytoplankton is not only a crucial component of ocean ecosystems, but should be considered in climate change models. This project will test two hypotheses: 1) latent phytoplankton viruses are highly diverse, abundant and pervasive in marine systems; 2) increasing ocean temperature is a key trigger for virus induction. The project will address these hypotheses by screening phytoplankton (culture collection and field samples) for latent infections using PCR-based methods and electron microscopy. Some samples will be induced (using elevated temperature or UV irradiation to "switch on" the viruses) and the virus particles will be detected by flow cytometry. The PIs will then use a transformative approach of virus sorting, whole virus genome amplification and sequence analysis, to design diagnostic probes to assess latency in the environment. Broader Impacts of this study will derive mainly from interactions between the scientists directly involved in the research and students/general public. For example, results of research from this project will be discussed during an informal "Café Scientifique" program designed to share the latest scientific ideas with the general public. The PIs will teach K-12 students the structure of viruses and the principles of molecular probing using cardboard models during informal open days. The PIs will also incorporate a further "order of magnitude" (virus DNA) into the Keller-Bigelow Laboratory Orders Of Magnitude (BLOOM) program, designed to teach high school students, from throughout Maine, functionality in marine ecosystems. Outcomes from BLOOM include understanding methods of investigation and broadening and strengthening the students' interest in science. The PIs have links with local schools, having visited pre-K to 3 children to teach them about phytoplankton and viruses and hosted a high school work experience student in the laboratory, who helped to isolate and characterize viruses from a marine hatchery. The PIs will host undergraduate interns and will interact with postgraduate students through our collaborators during the course of this project. The key product of this research will be information on virus latency in marine phytoplankton, of which almost nothing is currently known. Phytoplankton and their viruses are vital components in the global carbon cycle. Findings from this project will further the understanding of these important viruses, their propagation and survival strategies. Genome sequence information of these viruses will encourage involvement from biotechnology companies who are actively seeking novel enzymes, compounds and processes in the marine environment. In addition, since some of the algal hosts studied in this project (zooxanthellae) are coral symbionts, the findings will also be relevant to coral biology, and in particular to the understanding of coral bleaching, which results from loss of zooxanthellae, and is thought to be associated with increased temperature. The fate of the World's coral reefs is of great interest and concern to the general public.