Feeding responses of marine phagotrophic protists: cell biological mechanisms

噬食性原生生物作为细菌和浮游植物生物量的主要消费者和转化者，在海洋浮游食物网中发挥着核心作用。原生动物食草动物可以表现出复杂的摄食反应，包括选择性摄食或回避，基于猎物细胞的特性。这种选择性有可能影响海洋中的碳循环。阐明海洋食食性原生生物可能选择性地针对不同类型的猎物的生化机制对于理解海洋食物网的结构和功能至关重要。研究人员已经展示了初步结果，这些结果表明原生生物的摄食行为，包括化学感受反应和猎物摄取，实际上涉及基本的细胞生物学机制：即配体化合物与细胞膜相关的受体分子结合，这激活了细胞内信号转导途径，导致细胞生物化学和行为的变化。他们将研究信号化合物与原生生物细胞膜上受体分子结合的作用，以及控制原生生物对猎物的化学感受反应和猎物摄取的信号转导级联。该项目将包括1）对已知和最近分离的海洋原生生物物种进行实验，然后是2）对从俄勒冈州沿海海水中生长出来的原生生物组合进行实验。这项研究将集中在确定配体结合和信号转导过程控制原生生物摄食行为的程度，以及细胞表面配体-受体结合的差异在多大程度上可以解释替代类型的猎物之间的选择性。该办法将包括：1）药理学方法：由糖和凝集素组成的糖微阵列，以测试原生生物和猎物细胞膜上特异性糖-凝集素结合位点的存在，以及使用特异性蛋白激酶、G蛋白和G蛋白连接受体的选择性抑制剂来测试信号转导途径在海洋原生生物摄食行为中的作用，和2）设计用于显示配体-凝集素结合的特异性，以及是否细胞内信号转导机制，有一个显着的作用，在猎物的选择性/开关和捕食率的原生生物隔离物和异养flagellates.Intellectual优点：原生生物摄食反应的生化机制可能是理解这一重大的自上而下的控制在海洋系统中的微生物种群。这项研究采用了药理学/细胞生物学中使用的方法，这种方法可能会导致与海洋微生物生态学相关的新发现，并采用新方法评估原生动物食草动物的原位影响。更广泛的影响：该项目将支持一名研究生的博士论文研究，也将涉及一名本科生的实验。该项目的成果将通过介绍、出版物、讲座和调查人员网站传播。

Phagotrophic protists play a central role in marine pelagic food webs as major consumers and remineralizers of bacterial and phytoplankton biomass. Protistan grazers can show complex feeding responses, including selective ingestion or avoidance, based on characteristics of prey cells. Such selectivity has the potential to affect carbon cycling in the sea. Elucidating the biochemical mechanisms by which marine phagotrophic protists might selectively target distinct types of prey is vital to understanding the structure and function of marine food webs. The investigators have shown preliminary results which show that protistan feeding behavior, including chemosensory response and prey ingestion, does in fact involve basic cell biological mechanisms: i.e. binding of ligand compounds to receptor molecules associated with cell membranes, which activates intracellular signal transduction pathways leading to changes in cell biochemistry and behavior. They will conduct an investigation of the role of binding of signal compounds to receptor molecules on protistan cell membranes, and of the consequent signal transduction cascades in controlling protistan chemosensory response to prey, and prey ingestion. This project will involve 1) experiments with both known and recently isolated species of marine protists, followed by 2) experiments with protist assemblages grown up from Oregon coastal seawater. The research will focus on determination of the extent to which ligand binding and signal transduction processes control protist feeding behavior, and the extent to which differences in cell-surface ligand-receptor binding can explain selectivity between alternate types of prey. The approach will include: 1) pharmacological methods: glycomic microarrays composed of sugars and lectins to test for the presence of specific sugar-lectin binding sites on protist and prey cell membranes, and use of selective inhibitors of specific protein kinases, G proteins, and G protein-linked receptors to test for the role of signal transduction pathways in the feeding behavior of marine protists, and 2) experiments designed to show whether specificity of ligand-lectin binding, and whether intracellular signal transduction mechanisms, have a significant role in prey selectivity/switching and rates of prey ingestion by protist isolates and by in situ assemblages of heterotrophic flagellates.Intellectual merit: The biochemical mechanisms underlying protistan feeding response are likely to be fundamental to understanding this major top-down control of microbial populations in marine systems. This study adapts approaches used in pharmacology/cell biology in a way that could result in new discoveries relevant to marine microbial ecology, and in novel approaches to assessing the in situ impact of protist grazers. Broader impacts: This project will support the PhD thesis research of a graduate student and will also involve an undergraduate student in the experiments. Results of the project will be disseminated through presentations, publications, lectures, and the investigators' website.