Collaborative Research: Diversity and ecological impacts of Antarctic mixotrophic phytoplankton

传统的海洋食物链模式包括光合作用的藻类(浮游植物)被小动物(浮游动物)摄取，大型动物(鱼)摄取。这些传统的模型发生了变化，因为新的方法使得人们能够认识到细菌和其他非光合作用的原生动物在更复杂的食物网中的重要性。最近，混合营养生物(既可以光合作用又可以摄取食物颗粒的生物)的广泛存在及其作为微生物捕食者的重要性在许多海洋地区得到了承认。在南大洋，仅有的两次对混合营养生物的调查表明，它们作为捕食者的重要性可能存在季节性差异。在漫长的极地夜晚(冬季)，混合营养生物摄取颗粒食物的能力可能有助于它们的生存，从而确保一旦光合作用速率增加，春季有足够的种群支持浮游植物的水华。因此，混合营养生物可能是浮游动物和大型动物生长和繁殖所依赖的一个重要的早期食物来源。该项目将促进对南大洋微生物食物网内混合营养生物多样性及其生态影响的了解。具体而言，将重点关注南极洲西部半岛地区春季和秋季的混合营养，届时光合作用和摄食对混合营养生物的相对重要性可能会发生变化。该项目将为本科生和研究生以及博士后研究员提供研究机会。将通过博客和采访从南大洋实时接触公众，并通过一个融合科学和艺术教育的既定项目接触高中艺术学生。尽管传统观点认为原生生物是“光养的”或“异养的”，但仍有许多光合作用的原生生物会捕食猎物(混合营养)。混合营养是水生系统和浮游植物群落中的一种普遍现象，南极水域中存在并经常丰富的混合营养物种，特别是金藻、隐芽植物、裸藻和甲藻。然而，在南大洋，混合营养型植物鞭毛虫的存在只被调查过两次：2008年春季和2011年夏季在罗斯海。该项目的主要目标是更好地了解混养生物的多样性及其对南大洋微生物食物网的生态影响。混合营养生物对初级生产和细菌消耗的贡献可能与群落的分类组成和特定物种的丰度有关。将通过定量聚合酶链式反应来评估新的混合营养物种的丰度，这将与取食速率和光合作用的评估相结合，目的是描述活跃的混合营养生物如何引导碳通过食物网的移动。这些实验将有助于确定混合营养在极地水域作为一种营养策略的可行性和广泛性，并提供关于在南半球春季和秋季不同环境条件下目前未知的混合营养类群多样性的直接信息。此外，这些方法将同时产生关于整个原生生物群落的信息-混合营养、光营养和异养。此外，还将采用一种方法来研究食菌/混合营养群落的分类和功能多样性。胸腺嘧啶核苷类似物(BrdU)将被用于标记以细菌为食的真核生物的DNA。用免疫沉淀法分离BrdU标记的真核DNA。对标记的DNA(食菌体)和未标记的群落DNA的高通量测序将确定与其他微真核生物相比的食菌混合营养生物的多样性。以叶绿素为基础的流式细胞术分选，以关注混合营养物种。这些方法将阐明目前对不同条件下南大洋微生物相互作用影响的认识差距。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Traditional models of oceanic food chains have consisted of photosynthetic algae (phytoplankton) being ingested by small animals (zooplankton), which were ingested by larger animals (fish). These traditional models changed as new methods allowed recognition of the importance of bacteria and other non-photosynthetic protozoa in more complex food webs. More recently, the wide-spread existence of mixotrophs (organisms that can both photosynthesize and ingest food particles) and their importance as microbial predators has been recognized in many oceanographic areas. In the Southern Ocean, the only two surveys of mixotrophs have suggested that there may be seasonal differences in their importance as predators. During the long polar night (winter), the ability of mixotrophs to ingest particulate food may aid in their survival thus ensuring a sufficient population in spring to support a phytoplankton bloom once photosynthesis rates can increase. Thus mixotrophs may provide a critical early food source upon which zooplankton and larger animals depend on for growth and reproduction. This project will advance understanding of mixotroph diversity and their ecological impact within the Southern Ocean microbial food web. Specifically, efforts will be focused on mixotrophy in the western Antarctica peninsula region during the austral spring and autumn when there are likely to be changes in the relative importance of photosynthesis and ingestion to mixotrophs. The project will provide research opportunities for undergraduate and graduate students and a post-doctoral researcher. There will be real-time outreach from the Southern Ocean to the public via blogs and interviews, and to high school art students through an established program that blends science and art education. Despite traditional views of protists as either "phototrophic" or "heterotrophic," there are many photosynthetic protists that consume prey (mixotrophy). Mixotrophy is a widespread phenomenon in aquatic systems and phytoplankton groups with known mixotrophic species, notably chrysophytes, cryptophytes, prymnesiophytes, prasinophytes and dinoflagellates, are present and often abundant in Antarctic waters. However, in the Southern Ocean, the presence of mixotrophic phytoflagellates has been surveyed only twice: in the Ross Sea during Austral spring 2008 and summer 2011. The primary goals of the project are to gain better understanding of mixotroph diversity and their ecological impact with respect to the Southern Ocean microbial food web. The contribution of mixotrophs to primary production and bacterial consumption is likely linked to the taxonomic composition of the community and the abundance of particular species. Abundances of novel mixotrophic species will be evaluated via qPCR, which will be coupled with assessments of rates of feeding and photosynthesis with the goal of describing how active mixotrophs direct the movement of carbon through food webs. These experiments will help the determination of how viable and widespread mixotrophy is as a nutritional strategy in polar waters and give direct information on the currently unknown diversity of mixotrophic taxa under different environmental conditions occurring in austral spring and autumn. Furthermore, the methods will simultaneously yield information on the whole communities of protists - mixotrophic, phototrophic and heterotrophic. In addition, a method to examine aspects of the taxonomic and functional diversities of the bacterivorous/mixotrophic community will be employed. A thymidine analog (BrdU) will be used to label DNA of eukaryotes feeding on bacteria. The BrdU-labeled eukaryotic DNA will be isolated using immunoprecipitation. High-throughput sequencing of the labeled DNA (bacterivores) versus unlabeled community DNA will determine the diversity of bacterivorous mixotrophs relative to other microeukaryotes. Flow cytometric sorting based on chlorophyll to focus on mixotrophic species. These approaches will elucidate a gap in current knowledge of the influence of microbial interactions in the Southern Ocean under different conditions.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.