EAGER: Challenging the broadcast allelopathy paradigm in toxigenic microbial eukaryotic ecology

沿海海洋和淡水系统中的有害藻类大量繁殖对人类和野生动物的健康构成日益严重的关切，特别是当这些有害藻类大量繁殖产生毒素时。在过去的20年里，入侵性的、形成水华的金藻（Prymnesium parvum）已经蔓延到20多个州，造成大量鱼类死亡，并威胁到许多内陆休闲和商业渔业。虽然对金藻毒素的化学性质和影响了解很多，但对这些毒素产生的原因、产生的机制或将其传递给目标生物（如鱼类）的方式了解较少。长期以来，研究人员一直认为，黄金藻毒素是在压力时期（如缺乏足够的营养物质）产生的，并释放到周围的水中，以杀死潜在的竞争对手和猎物，从而释放出以前无法获得的营养物质并缓解压力。然而，事实上，这一假设缺乏理论考虑和实验数据的支持。这项研究挑战了这种长期存在的藻类毒性范式，并将实验与遗传，基因组和分析化学方法相结合，旨在明确描述这些毒素是如何产生和调节的，以及金藻如何使其他生物体暴露于这些毒素。预期成果可以改变目前的毒性模式，并在尽量减少与接触藻毒素有关的人类和野生动物健康风险的背景下，导致今后在了解有害藻华方面取得重大进展。广布化感作用是原生生物毒性研究的主流范式，缺乏令人信服的理论和实验支持。这项NSF支持的研究的目的是提供清晰和有意义的分析毒素的生产和交付的产毒附着植物Prymnesium parvum。实验方法是双重的，涉及1）在捕食者-猎物相互作用期间毒素的新分析检测，以及2）用于生物发生和异养营养获取的基因组指导的遗传基础。其核心假设是，亲源原生生物使用直接的细胞与细胞接触来传递毒素，随后吸收和运输猎物细胞成分穿过细胞膜。这项研究的基本原理是最近的实验证明，P. parvum的毒性是由直接的猎物接触介导的，以及理论上的考虑，通过扩散传递外毒素是不太可能的，不利于个体P. parvum细胞的适应性。这项研究是重要的，因为它将阐明一个基本的过程，通过该过程，捕食和异养支持在转基因原生生物，从而有可能改变目前的毒性范式，明确确定一种机制，毒素交付，将提供一个健身优势，而不需要组选择参数。这项研究的结果将导致未来的工作集中在原生生物细胞-细胞相互作用的机制，原生生物毒素的生理和生化作用，毒性在水华形成中的作用的重新评估，以及探索其他原生生物类群和水生系统中的有害藻类毒素的模型。

Harmful algal blooms in coastal marine and freshwater systems represent a serious and growing concern for human and wildlife health, particularly when these blooms of harmful algae that produce toxins. The invasive, bloom-forming alga Prymnesium parvum (aka, golden algae) has spread to more than 20 states in the last two decades, causing massive fish kills and threatening many inland recreational and commercial fisheries. While a good deal is known about the chemical nature and effects of golden algal toxins, less is understood with respect to why these toxins are produced, the mechanisms by which they are produced, or the means by which they are delivered to targeted organisms, such as fish. Researchers have long thought that golden algal toxins are produced during times of stress (as with a lack of sufficient nutrients) and released into the surrounding water to kill potential competitors and prey, thus freeing previously unavailable nutrients and alleviating the stress. In truth, however, this hypothesis is poorly supported by theoretical considerations and experimental data. This research challenges this long-standing paradigm of algal toxicity and, with the novel combination of experimentation with genetic, genomic, and analytical chemical approaches, aims to explicitly characterize how these toxins are produced and regulated, and how golden algae expose other organisms to these toxins. Expected results could transform the current toxicity paradigm and lead to significant future advances in the understanding of harmful algal blooms within the context of minimizing human and wildlife health risks associated with exposure to algal toxins. Broadcast allelopathy, the prevailing paradigm in protistan toxicity, lacks convincing theoretical or experimental support. The objective of this NSF-supported research is to provide clear and meaningful analysis of toxin production and delivery in the toxigenic haptophyte Prymnesium parvum. The experimental approach is twofold, involving 1) novel analytical detection of toxins during predator-prey interactions, and 2) a genome-guided genetic foundation for toxigenesis and heterotrophic nutrient acquisition. The central hypothesis is that toxigenic protists use direct cell-to-cell contact for delivery of toxins and subsequent uptake and transport of prey cell constituents across the cell membrane. The underlying rationale of this research is the recent experimental demonstration that toxicity of P. parvum is mediated by direct prey contact, as well as the theoretical consideration that delivery of exotoxins by diffusion is unlikely, and not advantageous to the fitness of individual P. parvum cells. This research is significant because it will elucidate a fundamental process through which predation and heterotrophy are supported in toxigenic protists, and will thereby potentially transform the current toxicity paradigm by definitively identifying a mechanism for toxin delivery that would provide a fitness advantage without the need for group selection arguments. Results of this study will lead to future work focused on the mechanisms of protistan cell-cell interactions, physiological and biochemical action of protistan toxins, reassessment of the role of toxicity in bloom formation, and a model for exploring other toxigenic protistan taxa and the multitude of harmful algal toxins in aquatic systems.