Marine Diatom-Parasite Relationships in Upwelling Systems

最近对海洋表层水域的一项全球调查显示，微生物寄生虫占真核浮游生物多样性的一半，并表明生物相互作用，包括寄生虫，在许多类型的微观藻类的生态学中发挥重要作用，这些藻类是海洋食物网的基础，但不是硅藻。硅藻是最丰富的微藻之一，特别是在上升流地区，那里营养丰富的深海洋流滋养着海洋表面，支撑着世界上最大的渔业。然而，这项调查没有调查高生产率地区，留下了重大的知识差距。硅藻在上升流地区可能会成功，因为它们躲避了捕食者和寄生虫，但似乎更合理的是，它们像所有其他微藻一样，也有生物敌人。在这项研究中，研究人员使用了大量来自上升流地区的可用样本来研究寄生虫对硅藻群落增殖和由此产生的初级生产的影响。该项目支持一名研究生，并为高中生和本科生提供实践研究经验。研究数据也被整合到首席研究员教授的课程中。塔拉海洋序列数据库中真核生物多样性的一半属于推定的寄生微生物，这一发现意味着我们对初级生产生物控制的理解发生了革命。生态系统模型才刚刚开始纳入病毒对生产和群落组成的影响，但真核寄生虫增加了另一个维度，具有潜在的巨大生物地球化学意义。虽然病毒捕食通常被认为将物质通量从食草动物转移到溶解的有机碳库中，增加了群落多样性和微生物生物量，但转化为寄生虫生物量的浮游植物生物量对食草动物来说是可利用的。在自然系统中，寄生虫活性的实验测定是困难的，因此大多数真核寄生虫的多样性、丰度和宿主相互作用的证据都是基于DNA序列数据。塔拉海洋数据库表明，硅藻很少有生物相互作用，导致对自下而上因素（如营养物质）的依赖性更强。然而，该数据库并不代表高生产力上升流地区。该项目提出了两个假设：1)在高产的偶发性上升流系统中，硅藻参与了宿主-寄生虫的相互作用，这种相互作用可以在水华期间的共现网络中确定；2)寄主-寄主对的群落组成和丰度在开花过程中随寄主密度的变化而变化。在本项目中，通过标签测序、宏基因组学和靶向qPCR，研究了上升流系统中寄生虫的丰度、多样性和动态，这些样本来自硅藻主导的上升流系统（加利福尼亚海流、东热带太平洋）、北大西洋春季水华的档案样本，以及两个由表面海水接种到富含硝酸盐的蒙特利湾海水中诱导的硅藻华的中游实验。这些样品的生物地球化学参数（营养、初级生产、硝酸盐同化等）是可用的。此外，研究小组正在利用网络和时间序列分析的生物信息学分析结果，发现宿主和寄生虫之间的联系。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。

A recent global survey of surface ocean waters revealed that microbial parasites comprise half of the eukaryotic plankton diversity and suggested that biological interactions, including parasites, play an important role in the ecology of many types of microscopic algae, which are the base of the ocean food web, but not diatoms. Diatoms are among the most abundant microalgae, particularly in upwelling areas where nutrient-rich deep currents feed the ocean's surface and support the world's greatest fisheries. Yet this survey did not investigate high-productivity regions, leaving a significant knowledge gap. Diatoms may be successful in upwelling regions because they evade predators and parasites, but it seems more reasonable that they, like all other microalgae, also have biological enemies. In this study, the researchers use a large set of available samples from upwelling regions to investigate the effect of parasites on the proliferation of diatom communities and resulting primary production. The project supports a graduate student and provides hands-on research experiences for high school and undergraduate college students. The study data are also integrated into courses taught by the principal investigator. The discovery that half of the eukaryotic diversity in the Tara Oceans sequence database belongs to putatively parasitic microbes implies a revolution in our understanding of biological control of primary production. Ecosystem models are only beginning to incorporate the effect of viruses on production and community composition, but eukaryotic parasites add yet another dimension with potentially vast biogeochemical implications. While viral predation is generally thought to divert material flux away from grazers and into the dissolved organic carbon pool, increasing community diversity and microbial biomass, phytoplankton biomass diverted into parasite biomass becomes available to grazers. Experimental determination of parasite activity is difficult in natural systems, so most of the evidence for diversity, abundance, and host interactions of eukaryotic parasites is based on DNA sequence data. The Tara Oceans database suggests that diatoms have very few biotic interactions, leading to a stronger dependence on bottom-up factors (e.g., nutrients). However, this database did not represent high productivity upwelling regions. This project addresses two hypotheses: 1) diatoms in highly productive episodic upwelling systems are involved in host-parasite interactions that can be identified in co-occurrence networks during blooms; and 2) the community composition and abundance of host-parasite pairs vary over the course of the bloom in a manner consistent with density dependence on the host. In this project, abundance, diversity, and dynamics of parasites in upwelling systems are investigated by tag sequencing, metagenomics, and targeted qPCR of diatom-parasite pairs identified from archived samples from diatom-dominated upwelling systems (California Current, Eastern Tropical Pacific), the North Atlantic Spring bloom, and from two mesocosm experiments of diatom blooms induced by inoculation of surface seawater into nitrate-rich Monterey Bay seawater. Biogeochemical parameters (nutrients, primary production, nitrate assimilation, etc.) for those samples are available. In addition, the research team is using the outputs of the bioinformatics analysis in network and time series analysis to discover links among hosts and parasites.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.