OCE-RIG: The chlorophyll 15N proxy for nitrogen cycling and export production: Understanding nitrogen isotope fractionations in chlorophyll biosynthesis

概述：在本项目中，研究者将采用多学科方法来了解蓝藻和真核藻类中与叶绿素生物合成相关的氮同位素分异。叶绿素降解产物的氮同位素比值是测定地表水氮不受成岩作用影响的重要新指标。沉积样品中叶绿素衍生的生物标志物可以保存数亿年，因此可以作为理解古代海洋氮循环的工具。此外，叶绿素15N含量的巨大分类群特异性差异允许使用沉积叶绿素色素和大量氮之间的15N补偿来重建蓝藻和真核藻类对出口生产的贡献。为了使用15N代色素，必须了解这些同位素分馏的差异。这项工作使用同位素箱模型方法来计算叶绿素生物合成途径中每一步的酶催化作用，以确定重要的催化作用发生的位置。叶绿素生物合成的纯化代谢中间体将测量其同位素组成。代谢组学技术，如动力学通量分析，将用于测量中间池的大小和沿路径分支点的通量。同位素、浓度和通量数据将被整合，以了解表达分馏的控制。知识价值：更好地理解藻类和蓝藻叶绿素中15N分异的控制，将改善一个强大的新的古海洋学代理的使用。除了这项工作对理解海洋氮循环的明显贡献之外，这种方法还为理解沉积记录中保存的有机分子的分异提供了一个新的框架。这些分子化石的同位素分析在古海洋学中有很大的用处，因为它可以将产生沉积有机质的生物的分类特征信息与它们的代谢或营养基质信息联系起来。该方法可直接应用于其他生物标志物系统。该方法的新颖之处在于它结合了稳定同位素地球化学和代谢组学的分析技术，代谢组学是生物医学研究的一个新兴领域，在生物地球化学研究中具有巨大的潜力。更广泛的影响：进一步开发具有多种应用的重要的新型化合物特异性同位素代用物将有助于我们对现代海洋氮循环的理解，这对于预测和减轻人为气候变化对海洋生物地球化学的影响具有重要意义。该项目将有助于改善STEM教育，增加女性对科学的参与。拟议的工作涉及对本科生实习生和一名女高中生进行培训和指导。在这个项目中，研究者通过正在进行的以海洋学为基础的小学课程设计工作参与了外联工作。该研究人员还积极参与努力，通过在她的部门建立一个妇女小组，并开展一系列讲座，将杰出的女性地球科学家带到她的部门进行为期多日的互动访问，重点是科学研究和指导。

Overview: In this project, the investigator will use a multidisciplinary approach to understand nitrogen isotope fractionations associated with chlorophyll biosynthesis in cyanobacteria and eukaryotic algae. Nitrogen isotope ratios of chlorophyll degradation products are an important new proxy for surface water nitrogen that is unaltered by diagenesis. Biomarkers derived from chlorophyll in sedimentary samples can be well preserved for hundreds of millions of years, and can therefore act as a tool for understanding ancient marine nitrogen cycling. Additionally, large taxon-specific differences in chlorophyll 15N fractionations allow for the use of 15N offsets between sedimentary chloropigment and bulk nitrogen to reconstruct the contribution of cyanobacteria and eukaryotic algae to export production. In order to use the chloropigment 15N proxy, these differences in isotopic fractionation must be understood. The work uses an isotope box model approach for calculating enzymatic fractionations at each step along the chlorophyll biosynthetic pathway in order to determine where important fractionations occur. Purified metabolic intermediates of chlorophyll biosynthesis will be measured for their isotopic composition. Metabolomics techniques such as kinetic flux profiling will be used to measure intermediate pool sizes and fluxes along pathway branch points. Isotope, concentration, and flux data will be integrated in order to understand the control of expressed fractionations. Intellectual Merit: A better understanding of the controls of 15N fractionations in algal and cyanobacterial chlorophyll will improve the use of a powerful new paleoceanographic proxy. Beyond the obvious contributions of this work to understanding marine nitrogen cycling, this approach provides a new framework for understanding fractionations of organic molecules that are preserved in the sedimentary record. Isotopic analysis of these molecular fossils has great utility in paleoceanography because it allows for linking of information on taxonomic identity of organisms that produce sedimentary organic matter with information about their metabolism or nutrient substrates. The proposed approach can be directly applied to other biomarker systems. The novelty in this approach lies in its combination of analytical techniques from stable isotope geochemistry and metabolomics, an emerging field in biomedical research that has tremendous potential in biogeochemical studies. Broader Impacts: Further development of an important new compound-specific isotope proxy with diverse applications will contribute to our understanding of the modern marine nitrogen cycle, which is important for predicting and mitigating the effects of anthropogenic climate change on marine biogeochemistry. This project will contribute to improving STEM education and increasing the participation of women in science. The proposed work involves training and mentoring of undergraduate interns and a female high school student. In conjunction with this project, the investigator is involved in outreach through ongoing work on oceanography-based elementary school curriculum design. The investigator is also actively involved in efforts to increase retention of women in geosciences by establishing a group for women in her department, and developing a lectureship series to bring prominent female geoscientists to her department for multi-day interactive visits that will focus on both scientific research and mentoring.