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型植物，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。一些氨基酸保留了最初的化学特征（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。这些独特的氮同位素特征被沿着传递给以浮游植物为食物的生物体，并贯穿整个食物网。因此，单个氨基酸的N同位素值可用于获得支持食物网的N源的同位素值，并估计生物在生物群、颗粒、珊瑚骨骼和沉积物中的营养位置。但是，这需要清楚地了解浮游植物产生的氨基酸的N同位素模式。本计画将探讨在使用相同氮源时，不同浮游植物是否会产生不同氮同位素型态的胺基酸。该项目还将研究同一种浮游植物产生的氮同位素模式是否在不同的生长和环境条件下发生变化。本研究的信息将提高在生态学和地球化学研究中使用氨基酸中的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相结合，重点是吸引公众参与，促进各级的多样性和包容性。三名研究生和一名博士后将参与这项研究。研究机会将提供给本科生，特别是那些有背景的。学生将通过麦克奈尔和路易斯斯托克斯联盟少数民族参与计划在得克萨斯州A M大学在科珀斯克里斯蒂，西班牙裔服务和少数民族服务机构招募。为了广泛分享成果，研究人员和学生将在德克萨斯州科珀斯克里斯蒂为当地K-12学生举办海洋科学讲座。新贝德福德高中（在马）夏季海洋实习生计划将从事这个项目。将举办关于藻华的公开讲座，并将撰写一篇关于同位素的儿童文章。该项目的成果也将纳入提交给切萨皮克湾方案、马里兰州有害藻华特别工作组和马里兰州沿海海湾科学技术咨询委员会的报告中。 利用不同氨基酸的氮同位素值（δ 15 N-AA）来反演食物网的氮源同位素特征和估计营养位置依赖于对食物网底部浮游植物产生的δ 15 N-AA的信息，而这些信息仍然知之甚少。这项研究旨在探索基础科学问题，以更好地了解浮游植物产生的δ 15 N-AA。1)在相同的氮营养盐和生长条件下，不同的浮游植物类群之间的δ 15 N-AA模式是否存在差异？硅藻中独特的δ 15 N-AA模式与其氮代谢的独特方面有关吗？2)浮游植物的生理变化是否由氮营养盐的有效性、氮的利用形式（铵态氮、硝酸盐和混合氮）和/或其他生长条件独立地产生δ 15 N-AA的显著变化？浮游植物样本将从受控养殖（例如，恒化器）实验和在墨西哥湾和切萨皮克湾的实地研究，特别是在近单种水华事件。利用这些新的分析方法，将首次对浮游植物中精氨酸、天冬酰胺、谷氨酰胺和组氨酸等多聚氨基酸的化合物和分子内δ 15 N产生新的认识。这项地面实况调查工作将促进对生物泵和有害藻华在环境相关生理条件下关键浮游植物物种产生的δ 15 N-AA模式的理解。这项工作的预期成果将使新的应用和更复杂的营养位置分析，海洋生物泵的效率研究，古，利用保存在自然档案中的氨基酸进行海洋学重建。该项目由生物和化学海洋学计划资助。该奖项反映了NSF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。

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.