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华对人类和野生动物的健康构成了严重和日益严重的关切，特别是当这些有害藻华产生毒素时。在过去的二十年里，这种侵入性的、形成水华的藻（又名金藻）已经蔓延到20多个州，造成大量鱼类死亡，并威胁到许多内陆娱乐和商业渔业。虽然人们对金藻毒素的化学性质和作用已经了解得很多，但人们对这些毒素产生的原因、产生的机制，以及它们如何被输送到目标生物（如鱼类）的了解却很少。长期以来，研究人员一直认为，金藻毒素是在压力时期（如缺乏足够的营养）产生的，并释放到周围的水中，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，减轻压力。然而，事实上，这一假设并没有得到理论考虑和实验数据的支持。本研究挑战了这种长期存在的藻类毒性范式，并结合了遗传、基因组和分析化学方法的实验，旨在明确表征这些毒素是如何产生和调节的，以及金藻是如何使其他生物暴露于这些毒素的。预期的结果可能会改变目前的毒性模式，并在最大限度地减少与接触藻类毒素有关的人类和野生动物健康风险的背景下，在了解有害藻华方面取得重大进展。播散化感作用是原生生物中毒的主流范式，缺乏令人信服的理论或实验支持。这项由美国国家科学基金会支持的研究的目的是为产毒性小樱草叶的毒素产生和传递提供清晰而有意义的分析。实验方法是双重的，包括1)在捕食者-猎物相互作用过程中对毒素进行新的分析检测，以及2)基因组引导的毒素生成和异养营养获取的遗传基础。核心假设是，产毒原生生物通过直接的细胞间接触来传递毒素，随后通过细胞膜摄取和运输猎物细胞成分。这项研究的基本原理是最近的实验证明，parvum的毒性是通过直接接触猎物介导的，以及理论上考虑外毒素不太可能通过扩散传递，并且不利于单个parvum细胞的适应性。这项研究具有重要意义，因为它将阐明一个基本的过程，通过这个过程，在产毒原生生物中捕食和异养得到支持，并因此有可能通过明确确定毒素传递机制来改变当前的毒性范式，该机制将提供适应性优势，而不需要群体选择论证。本研究的结果将引导未来的工作重点集中在原生生物细胞间相互作用的机制、原生生物毒素的生理生化作用、毒性在水华形成中的作用的重新评估，以及探索其他产毒原生生物分类群和水生系统中众多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.