Collaborative Research: Diversity and ecological impacts of Antarctic mixotrophic phytoplankton

传统的海洋食物链模型是由光合藻类（浮游植物）被小动物（浮游动物）摄取，小动物（浮游动物）被大动物（鱼类）摄取。随着新方法认识到细菌和其他非光合原生动物的重要性，这些传统模型发生了变化。在更复杂的食物网中。最近，在许多海洋学领域，广泛存在的混合营养体（既能光合作用又能摄取食物颗粒的生物）及其作为微生物捕食者的重要性已得到认识。在南大洋，仅有的两次对混合营养体的调查表明，它们作为捕食者的重要性可能存在季节性差异。在漫长的极夜（冬季），混合营养体摄取颗粒食物的能力可能有助于它们的生存，从而确保在春季有足够的数量，一旦光合作用速率增加，浮游植物就会大量繁殖。因此，混合营养物可能为浮游动物和大型动物的生长和繁殖提供了重要的早期食物来源。该项目将促进对混合营养物多样性及其在南大洋微生物食物网中的生态影响的理解。具体来说，在南方春季和秋季，光合作用和摄入对混合营养物的相对重要性可能会发生变化，届时将重点关注南极洲半岛西部地区的混合营养物。该项目将为本科生和研究生以及一名博士后研究员提供研究机会。南大洋将通过博客和采访向公众进行实时宣传，并通过一个已建立的将科学和艺术教育相结合的项目向高中艺术学生进行宣传。尽管传统观点认为原生生物要么是“光养的”，要么是“异养的”，但有许多光合作用的原生生物消耗猎物（混合营养）。混合营养是水生系统和浮游植物群中普遍存在的现象，其中已知的混合营养物种，特别是chrysophytes， cryptopphytes, prymnesiopophytes， prasinophytes和dinoflagellates，在南极水域存在并且通常丰富。然而，在南大洋，混合营养型鞭毛藻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合营养物的多样性及其对南大洋微生物食物网的生态影响。混合营养体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。新的混合营养物种的丰度将通过qPCR进行评估，这将与摄食和光合作用速率的评估相结合，目的是描述活跃的混合营养生物如何通过食物网指导碳的运动。这些实验将有助于确定混合营养作为一种营养策略在极地水域的可行性和广泛性，并为南方春季和秋季不同环境条件下混合营养类群目前未知的多样性提供直接信息。此外，这些方法将同时获得原生生物整个群落的信息——混合营养型、光营养型和异营养型。此外，将采用一种方法来检查细菌/混合营养群落的分类和功能多样性。胸腺嘧啶类似物（BrdU）将用于标记以细菌为食的真核生物的DNA。brdu标记的真核DNA将采用免疫沉淀法分离。高通量测序标记的DNA（细菌捕食者）与未标记的群落DNA将确定相对于其他微真核生物的嗜菌混合营养体的多样性。基于叶绿素的流式细胞分选聚焦于混合营养物种。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知识的空白。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.