Giant viruses in the open ocean: Is large size adaptive where cells are scarce?

病毒可以感染所有形式的生命。病毒是高度多样化的，多样性的一个方面是大小：病毒基因组的长度变化超过一千倍，病毒颗粒的大小变化近一百万倍。“巨型”病毒的发现令人震惊，因为它们在物理上比许多自由生活的微生物更大，编码的基因也更多。越来越多的证据表明，巨型病毒在海洋中广泛存在，种类繁多，但对它们的生态学仍有很多未知。哪些关键的生态权衡因病毒大小而异，从而允许大小病毒共存？这些权衡是否会导致病毒大小在不同栖息地的分布不同？这个项目旨在为感染浮游植物的病毒解答这些问题，浮游植物是海洋生产力的基础。这项研究还可以影响一系列不同的科学领域，因为病毒大小在其他生态系统和宿主相关微生物组中差异很大。对病毒大小的基本限制可能在各个系统中大致相似，但是驱动病毒大小的过程尚未在其中任何一个系统中得到彻底研究。该项目支持一名博士后研究员、两名研究生和本科生在综合科学方面的培训，包括实地、实验室和建模组件。国家科学基金会支持的本科生研究经验和夏威夷大学马诺阿分校的部落学院和大学项目为太平洋岛民和其他代表性不足的群体提供服务，用于招收学生。此外，夏威夷公共活动中的科学推广活动包括一个互动游戏，以交流有关巨型病毒及其在海洋中的作用的想法。与较小的病毒相比，大型病毒可能有四个优势：1)能够感染更多样化的宿主基因型，2)更好地控制宿主代谢，3)大到足以通过摄入进入宿主细胞，4)在细胞外环境中更持久。这些优势可能弥补较小的病毒所具有的优势：与宿主的接触率较高，每次感染的后代数量较多。在低营养生境中，大尺寸的优势可能更为重要，在那里，微生物真核生物群落主要是小的吞噬性鞭毛虫（混合营养体和异养体），种群密度低，资源有限。该项目的目标是：(1)根据该研究小组的初步观察，测试巨型病毒是否确实在贫营养海洋中占主导地位，而不是在生产丰富的沿海地区；(2)通过对不同病毒分离株进行实验室实验，验证以上四种关于大尺寸优势的假设；(3)利用真核微生物及其病毒的生态进化模型来解释观察到的大小模式。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Viruses can infect all forms of life. Viruses are highly diverse, and one aspect of diversity is size: genomes of viruses vary more than a thousandfold in length, and the size of viral particles varies nearly a millionfold. The discovery of “giant” viruses was astounding because they can be physically larger and code for more genes than many free-living microorganisms. There is growing evidence that giant viruses are widespread and diverse in the ocean, but much about their ecology remains unknown. What critical ecological tradeoffs vary with virus size, allowing small and large viruses to coexist? Do these tradeoffs cause the distribution of virus sizes to vary across habitats? This project aims to answer these questions for viruses that infect phytoplankton, the microscopic plants that are the foundation of ocean productivity. This research can also influence a diverse array of scientific fields because virus size varies greatly in other ecosystems and host-associated microbiomes. The fundamental constraints on size may be broadly similar across systems, but the processes driving virus size have not been thoroughly investigated in any of them. This project supports the training of a postdoctoral researcher, two graduate students, and undergraduate students in integrative science that includes field, laboratory, and modeling components. National Science Foundation-supported Research Experience for Undergraduates and Tribal Colleges and Universities programs at UH Manoa that serve Pacific Islanders and other underrepresented groups are used for recruiting students. In addition, science outreach at public events in Hawai’i includes an interactive game to communicate ideas about giant viruses and their role in the ocean. Large viruses may have four advantages over smaller viruses: i) ability to infect a greater diversity of host genotypes, ii) better control of host metabolism, iii) large enough size to enter host cells by ingestion, and iv) greater persistence in the extracellular environment. These advantages may compensate for the advantages held by smaller viruses: higher contact rates with their hosts and greater offspring number per infection. The advantages of large size may be more consequential in oligotrophic habitats, where the microbial eukaryote community is primarily small phagotrophic flagellates (mixotrophs and heterotrophs), at low population densities, with resource-limited growth. The project goals are: (1) To test whether giant viruses indeed dominate in the oligotrophic ocean compared to a productive coastal location, as suggested by initial observations of this research team; (2) To test the above four hypotheses about the advantages of large size by conducting laboratory experiments with diverse viral isolates, and (3) To use an eco-evolutionary model of eukaryotic microbes and their viruses to explain observed size patterns.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.