Collaborative research: Investigation of a phytoplankton DMSP-based chemical defense system active against protist grazers

化学防御？个人用来减少或消除致死剂的化学物质种类繁多，分布广泛，对物种间的相互作用很重要。与陆地和海洋底栖动物物种相比，对浮游生物的研究较少，尽管如此，化学防御被认为在构建浮游生物群落方面发挥了作用。它们在促进藻类水华的形成和持续方面可能特别重要。在最近由美国国家科学基金会资助的研究中，我们表明，球石虫Emily huxleyi对大多数测试过的原生食草动物物种具有化学防御作用。研究表明，至少有两个方面的硫化学成分可以降低原生生物的放牧率：高的DMSP裂解酶活性(DLA)和外源DMSP(二甲基磺酰丙酸酯)本身。由于海洋中同时存在高级浮游植物DLA和溶解的DMSP，我们认为这种防御系统对于使E.huxleyi水华的形成和持续具有重要意义。此外，由于许多形成水华的甲藻和裸子植物的胞内DMSP浓度很高，至少有些物种的DLA含量很高，这种化学防御系统可能对浮游植物水华的动态具有广泛的重要性。对DMSP“防御系统”的大量实验表明，DMSP对原生生物无毒。相反，这种亚致死防御系统可能是基于食草动物和猎物物种之间的细胞间化学通信。目前的建议是对这一防御体系的来源、作用机制(S)和意义进行调查，为实现这一目标，将进行多层次的调查。在天然水样和混合实验室组合中添加高裂解酶E.huxleyi细胞和防御性化学物质，将可以测试群落水平的防御效果，包括可能减少微型浮游动物的捕食，将觅食转移到其他猎物类型，以及对其他浮游植物物种的化感作用。种群水平的研究将揭示原生生物对防御的敏感性是否与原生生物分类群、摄食方式或大小有关。在个体和分子水平上，提出了DMSP？诱导的取食抑制机制的一系列可能性。将研究化学线索(DMSP裂解和氧化产物、藻类渗透物质)对原生生物摄食率和个体行为的影响，作为测试这些可能性的手段。BROADERIMPACT建议的研究将包括大量的研究生和本科生，包括香农点海洋中心海洋科学本科生项目的学生。其他外展活动将包括将概念、技术和研究成果纳入教学活动，并准备面向一般受众的网络和印刷材料。国际合作提高对亚致命化学防御的了解，因为它们涉及细胞信号，并最终使浮游植物水华的形成成为海洋学、生物科学和教育的一个令人兴奋的领域。通过帮助我们比较陆地、海洋底栖和浮游生态系统之间的化学防御理论，这种理解可以深入了解支配这些看似不同的生态系统的生物相互作用的生态和进化原则。

Chemical defenses ? chemicals used by individuals to reduce or eliminate agents of mortality are diverse, widespread, and important for species interactions. Less studied in planktonic organisms than in terrestrial and marine benthic species, chemical defenses are nonetheless thought to play a role in structuring planktonic communities. They may be particularly important in promoting the formation and persistence of algal blooms. In recent NSF?supported research, we showed that the coccolithophorid Emiliania huxleyi is chemically defended against most tested protist grazer species. At least two aspects of E. huxleyi sulfur chemistry were shown to reduce rates of protist grazing: high DMSP lyase activity (DLA), and exogenous DMSP (dimethylsulfoniopropionate) itself. As both high phytoplankton DLA and dissolved DMSP are present in the sea, we propose that this defense system is important in allowing E. huxleyi blooms to form and persist. Furthermore, as many bloom?forming dinoflagellate and prymnesiophyte species have high intracellular DMSP concentrations and at least some have high DLA, this chemical defense system may be of widespread importance for phytoplankton bloom dynamics. Numerous experiments on this DMSP "defense system" indicated that DMSP is not toxic to protists. Rather, this sublethal defense system might be based on intercellular chemical communication among grazer and prey species. The present proposal constitutes an investigation into the source, mechanism(s) of action, and significance of this defense system.To accomplish this goal, a multi?level investigation will be conducted. Addition of high lyase E. huxleyi cells and defense chemicals to natural water samples and mixed laboratory assemblages will allow testing of community?level defense effects, including possible reductions in microzooplankton grazing, transfer of grazing to other prey types, and allelopathic effects on other phytoplankton species. Population?level studies will reveal whether protist sensitivity to defenses is related to protist taxon, feeding mode, or size. On the individual and molecular levels, a spectrum of possibilities for the mechanism of DMSP?induced feeding inhibition is presented. The effects of chemical cues (DMSP cleavage and oxidation products, algal osmolytes) on protist feeding rates and individual behavior will be studied as a means of testing these possibilities.BROADERIMPACTSThe proposed study will include numerous graduate student and undergraduate participants, including students in Shannon Point Marine Center's Minorities in Marine Science Undergraduate Program. Other outreach activities will include incorporation of concepts, techniques and findings into teaching activities, and preparation of web and print materials aimed at a general audience.INTELLECTUAL MERITDeveloping an increased understanding of sublethal chemical defenses as they involve cell signaling and, ultimately, phytoplankton bloom formation is an exciting area for oceanography, biological sciences, and education. By contributing to our ability to compare chemical defense theory among terrestrial, marine benthic, and planktonic ecosystems, such understanding could yield insights into ecological and evolutionary principles that govern biological interactions across these seemingly diverse ecosystems.