Understanding microbial control of dissolved organic nitrogen (DON) in the ocean: New amino acid tracers for bacterial source and cycling of refractory DON

该奖项的全部或部分资金来自《2021年美国救援计划法案》(公法117-2)。全球氮循环中最神秘的组成部分之一是存在于海洋中的大量溶解的含氮有机分子(溶解有机氮，简称DON)。这些分子的身份大多不得而知，但它们在海洋的生物和地球化学循环中很重要，因为它们持续了数千年，而且在许多情况下，这些分子太复杂了，不适合食物网底部的简单生物使用。该项目将开发新的化学工具来了解这种材料，包括稳定同位素、放射性同位素和氨基酸的手性。这组新的示踪剂将共同关注海洋细菌作为持久性溶解有机氮的来源和创造者的作用。该项目将在实验室开始，该团队将首先在那里培养大量的海洋藻类。然后加入天然海洋细菌，研究人员将在创建的溶解氮材料中测量拟议的新示踪剂。这些数据将揭示拟议的示踪剂是如何工作的：它们是如何以及何时产生的，如果它们与细菌来源相对应，以及细菌降解可能如何影响它们。然后，调查人员将在加利福尼亚州海岸和太平洋中部的不同地点进行一系列实地考察，分离出大量自然溶解的有机氮。该团队将把在实验室中学到的东西与有史以来第一次对单个示踪剂分子进行的放射性碳测量结合起来应用。这些活动将共同打开一个新的窗口，了解关键的海洋溶解有机氮材料的来源和循环。该项目将支持研究生、博士后研究员和来自代表性不足群体的本科生的教育、培训和职业发展，他们将被招募接受实际的实验室和现场经验。该项目将开发三种新的基于氨基酸的细菌来源和溶解有机氮变化的替代物：1)化合物特有的必需氨基酸的稳定碳同位素指纹，2)最近发现的一套新的D-氨基酸集中在放射性碳旧的低分子DON材料中，以及3)关键示踪氨基酸的单个氨基酸的放射性碳值。研究人员假设，难熔的海洋DON本质上完全是微生物，然而，就其来源、分子组成，特别是循环速度而言，它的多样性也远远超过了人们之前所了解的。特别是，该项目将测试在整个水柱中高和低分子量DON组分中完全不同的DON来源、分子组成和循环速率的想法。自养和异养细菌生长/降解实验将测试D/L的来源和与降解相关的变化的假设以及稳定的碳同位素特征。概括地说，将这些测量与高生产力沿海与低营养太平洋环流DON在表层和深海中的单个氨基酸放射性碳值一起进行测量，将使您能够首次了解DON细菌来源的多样性、降解影响和特定于N的循环率。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。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).One of the most mysterious components of the global nitrogen cycle is the vast amount of dissolved nitrogen-containing organic molecules (dissolved organic nitrogen, or “DON”) which exist in the ocean. The identities of these molecules are mostly unknown, but they are important in the ocean’s biological and geochemical cycles, because they persist for many thousands of years and in many cases these molecules are too complex for simple organisms at the base of the food web to use. This project will develop new chemical tools to understand this material, including stable isotopes, radioisotopes, and the chirality of amino acids. Together, this new set of tracers will focus on the roles of marine bacteria as sources and creators of persistent dissolved organic nitrogen. The project will begin in the laboratory, where the team will first grow large cultures of ocean algae. Natural ocean bacteria will then be added, and investigators will measure the proposed new tracers in dissolved nitrogen materials created. These data will reveal how the proposed tracers work: how and when they are produced, if they map to bacterial sources, and how bacterial degradation may affect them. The investigators will then conduct a series of field expeditions at contrasting sites on the California coast and in the central Pacific Ocean, isolating large amounts of natural dissolved organic nitrogen. The team will apply what has been learned in the lab together with the first ever radiocarbon measurements on individual tracer molecules. Together these activities will open a new window into sources and cycling of the critical marine dissolved organic nitrogen material. The project will support the education, training, and career development of a graduate student, a postdoctoral researcher, and undergraduate students from underrepresented groups, who will be recruited to receive real hands-on laboratory and field experience. This project will develop three new amino acid–based proxies for bacterial source and alteration of dissolved organic nitrogen: 1) compound-specific stable carbon isotope fingerprinting of essential amino acids, 2) a recently discovered suite of new D-amino acids found to be concentrated in radiocarbon-old, low molecular weight DON material, and 3) individual amino acid radiocarbon values for key hypothesized tracer amino acids. The investigators hypothesize that refractory ocean DON is essentially completely microbial, however that it is also far more diverse than has previously been understood in terms of its sources, molecular composition, and especially cycling rates. In particular, the project will test the idea of completely different DON origin, molecular composition, and cycling rates in high vs. low molecular weight DON fractions throughout the water column. Autotrophic and heterotrophic bacterial growth / degradation experiments will test assumptions about the sources and degradation- related changes to D/L and stable carbon isotope signatures. Synoptically making these measurements together with individual amino acid radiocarbon values in high productivity coastal vs. oligotrophic Pacific gyre DON in both surface and deep ocean will allow understanding the diversity of DON bacterial sources, degradation impacts, and N-specific cycling rates for the first time.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.