Collaborative Research: Phylogenetic and Physiological Characterization of Amino Acid Nitrogen Isotopes in Phytoplankton

浮游植物是生活在海洋中的微小植物，是海洋食物网的基础。这些微生物利用水中的无机氮(N)来制造各种氨基酸。有些氨基酸保留了其N源的初始化学特征（即N同位素值）。其他氨基酸参与改变初始化学特征（N同位素值）的代谢过程。这些不同的N同位素特征被传递给消耗浮游植物的生物和整个食物网。因此，单个氨基酸的N同位素值可以用来获得支持食物网的N来源的同位素值，并估计生物在生物群、颗粒、珊瑚骨架和沉积物中的营养地位。但是，这需要对浮游植物产生的氨基酸的N同位素模式有一个清晰的认识。本项目将研究在使用相同的氮源时，不同种类的浮游植物是否产生具有不同N同位素模式的氨基酸。该项目还将研究同一种浮游植物产生的N同位素模式在不同生长和环境条件下是否会发生变化。本研究的信息将提高在生态和生物地球化学研究中使用氨基酸N同位素值的能力。这个合作项目将新颖的研究与更广泛的影响结合起来，重点是吸引公众，促进各个层面的多样性和包容性。3名研究生和1名博士后将参与研究。为本科生，特别是有背景的本科生提供研究机会。学生将通过德克萨斯州农工大学科珀斯克里斯蒂分校的麦克奈尔和路易斯·斯托克斯少数民族参与联盟项目招募，这是一个为西班牙裔和少数民族服务的机构。为了更广泛地分享研究成果，研究人员和学生们将为德克萨斯州科珀斯克里斯蒂当地的K-12学生做关于海洋科学的演讲。新贝德福德高中（位于马萨诸塞州）的暑期海洋实习项目将参与该项目。将举行关于藻华主题的公开讲座，并将写一篇关于同位素主题的儿童文章。该项目的成果也将被纳入向切萨皮克湾项目、马里兰州有害藻华工作组和马里兰州沿海湾科学技术咨询委员会的报告中。利用不同氨基酸（δ15N-AA）的N同位素值来检索食物网N源同位素特征并估计营养位置，取决于食物网底部浮游植物产生的δ15N-AA信息，这一信息目前尚不清楚。本研究旨在探索浮游植物产生δ15N-AA的基本科学问题。1)在相同的氮养分和生长条件下，主要浮游植物类群的δ15N-AA模式是否存在差异？硅藻中独特的δ15N-AA模式是否与其氮代谢的独特方面有关？2)浮游植物的生理变化是否由氮养分有效性、利用的氮形式（铵态氮、硝态氮和混合氮）和/或其他生长条件单独引起δ15N-AA的显著变化？浮游植物样本将从受控培养（例如，恒化剂）实验和墨西哥湾和切萨皮克湾的实地研究中收集，特别是在几乎单一的水华事件期间。利用新发展的分析方法，将首次产生关于浮游植物中精氨酸、天冬酰胺、谷氨酰胺和组氨酸等多n AA化合物和分子内δ15N的新知识。这项实地调查工作将有助于了解与环境相关的生理条件下，对生物泵和有害藻华至关重要的关键浮游植物产生的δ15N-AA模式。这项工作的预期结果将使新的应用和更复杂的营养位置分析、海洋生物泵效率的研究以及利用自然档案中保存的氨基酸进行古海洋重建成为可能。本项目由生物和化学海洋学计划资助。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。

Phytoplankton are microscopic plants that live in the ocean and act as the base of the marine food web. These microorganisms use inorganic nitrogen (N) from the water to make a variety of amino acids. Some of the amino acids keep the initial chemical signature (i.e., N isotope value) of their N source. Other amino acids are involved in metabolic processes that change the initial chemical signature (N isotope value). These distinct N isotope signatures are passed along to organisms that consume phytoplankton and throughout the food web. Thus, the N isotope values of individual amino acids can be used to obtain the isotope value of N sources supporting food webs and to estimate the trophic position of organisms in biota, particles, coral skeletons, and sediments. But, this requires a clear understanding of the N isotope patterns of amino acids produced by phytoplankton. This project will examine whether different phytoplankton species produce amino acids with distinct N isotope patterns when using the same N source. The project will also study whether the N isotope patterns produced by the same species of phytoplankton change under different growth and environmental conditions. Information from this study will improve the ability to use N isotope values in amino acids in ecological and biogeochemical studies. This collaborative project combines novel research with broader impacts focused on engaging the public and promoting diversity and inclusion at various levels. Three graduate students and one postdoc will participate in the research. Research opportunities will be provided to undergraduate students, especially those with backgrounds. Students will be recruited through the McNair and Louis Stokes Alliances for Minority Participation program at Texas A&M Univ. at Corpus Christi, a Hispanic Serving and Minority Serving Institution. To share results broadly, the investigators and students will give talks about marine science to local K-12 students in Corpus Christi TX. The New Bedford High School (in MA) summer marine intern program will be engaged in this project. Public lectures will be given on the topic of algal blooms and a children’s article will be written on the topic of isotopes. Outcomes of this project will also be incorporated into presentations to the Chesapeake Bay Program, Maryland Harmful Algal Bloom Task Force, and the Scientific and Technical Advisory Committee of the Maryland Coastal Bays. The use of N isotope values of different amino acids (δ15N-AA) to retrieve the N source isotope signature of food webs and estimate trophic positions depends on information about the δ15N-AA produced by phytoplankton at the base of the food web which is still poorly understood. This study seeks to explore fundamental scientific questions to better understand δ15N-AA produced by phytoplankton. 1) Under the same nitrogenous nutrient and growth conditions, do δ15N-AA patterns vary between major phytoplankton groups? Are the unique δ15N-AA patterns in diatoms related to unique aspects of their N metabolism? 2) Do changes in phytoplankton physiology resulting from nitrogenous nutrient availability, N form utilized (ammonium, nitrate, and mixed), and/or other growth conditions independently produce significant changes in δ15N-AA? Phytoplankton samples will be collected from controlled culture (e.g., chemostat) experiments and from field studies in the Gulf of Mexico and Chesapeake Bay, especially during near-monospecific bloom events. By taking the advantage of newly developed analytical approaches, new knowledge of compound and intramolecular δ15N of poly-N AA such as arginine, asparagine, glutamine, and histidine in phytoplankton will be generated for the first time. This ground-truthing work will advance the understanding of δ15N-AA pattern produced by key phytoplankton species critical to the biological pump and harmful algal blooms under environmentally relevant physiological conditions. The expected outcomes from this work will enable new applications and more sophisticated trophic position analyses, studies of the efficiency of the ocean’s biological pump, and paleo-oceanographic reconstructions using amino acids preserved in natural archives.This project is funded by the Biological and Chemical Oceanography Programs.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.