Collaborative Research: Assessing the role of compound-specific phosphorus hydrolase transformations in the marine phosphorus cycle

磷(P)是生命的重要组成部分。由于磷在海洋的大片区域缺乏，磷的有效性可能控制生物生产力，如光合作用和固碳，这对温室气体二氧化碳的吸收和气候调节具有影响。海洋微生物必须通过从海水中获取磷来满足其营养需求，海水中磷以各种化学形式存在，从简单的磷酸根离子(PI)到复杂的溶解有机磷(DOP)分子。在大多数海洋区域，DOP的浓度远远超过PI，因此DOP是海洋微生物营养和生产力的重要磷来源。然而，关于特定DOP化合物对海洋微生物群落的磷营养、生产力和结构的贡献，仍有许多未知之处。在这个项目中，研究人员将在大西洋进行现场实验，并使用纯酶和微生物培养进行一系列对照实验室研究，以确定不同的DOP化合物在海洋环境中如何以及在多大程度上被降解为PI。此外，还将确定这些化合物特有的DOP分子对微生物磷营养、固碳和群落结构的贡献，从而促进对控制海洋微生物物种活动和分布的因素以及海洋在气候系统中的作用的认识现状。该项目将支持两名女性初级研究员、一名博士后研究员以及研究生和本科生。这些本科生将从萨凡纳州立大学的海洋科学项目中招收，萨凡纳州立大学是一所历史上的黑人学院和大学。此外，成果将被纳入新的动手K-12教育工具，向学生传授微生物磷生物地球化学，包括一个数字游戏和带有动手演示的正式教案。这些工具将与K-12教育工作者进行验证，并将通过各种知名的在线平台广泛向公众开放。因此，这些活动将惠及广大受众，包括相当一部分代表不足的群体。P是生命的重要营养。海洋微生物利用P-水解酶，如碱性磷酸酶(AP)，从各种溶解的有机磷(DOP)化合物中释放和获得磷(PI)，包括P-酯(P-O-C键)、磷酸盐(P-C)和聚磷酸盐(P-O-P)。化合物特有的DOP转化有可能对海洋微生物生态(例如物种间不同的DOP生物有效性)、生物地球化学(例如通过形成钙PI进行的P地质封存)和全球气候(例如通过甲基膦酸脱磷化产生温室气体甲烷)产生关键和广泛的影响。然而，除了对微生物群落水平的磷需求、生产力和结构的相对贡献外，特定DOP转化的机制和相对大小还不完全清楚。这项研究将通过跟踪海洋环境中特定DOP池的命运来填补这些知识空白。具体地说，该项目将在实验室使用代表来自高营养和低营养环境的海洋真核和原核生物浮游生物的重组酶和无菌培养，并在现场使用沿大西洋自然等电点梯度的观察和实验方法来验证四个假设。特别是，研究人员将揭示特定DOP化合物在群落-(散装酶分析)、分类-(天然样品中放射性标记细胞的细胞分类)、物种-(无菌培养)和分子水平(纯酶动力学研究和细胞相关蛋白质组和外蛋白质组)的水解和利用方面的潜在差异。我们拟议的工作结果将提供对特定形式DOP转化所涉及的酶基础的深入了解，并创造关于这些特定磷源对磷素生产、海洋微生物营养、群落结构、初级生产力以及全球碳循环和气候的相对贡献的新知识。特别是，我们对生物可用DOP浓度的精确测量和我们对DOP再矿化通量的独特估计将为改进海洋初级生产力和P循环模型提供关键的新信息。

Phosphorus (P) is an essential building block for life. Because P is in short supply over vast areas of the ocean, P availability may control biological productivity, such as photosynthesis and carbon fixation, which has implications for uptake of the greenhouse gas carbon dioxide and thus climate regulation. Marine microorganisms must satisfy their nutritional requirement for P by obtaining it from seawater, where P is present in a variety of chemical forms, from simple phosphate ions (Pi) to complex dissolved organic phosphorus (DOP) molecules. The concentration of DOP vastly exceeds Pi over most ocean areas, therefore DOP is a critically important source of P for marine microbial nutrition and productivity. However, much remains unknown about the contribution of specific DOP compounds to the P nutrition, productivity, and structure of marine microbial communities. In this project, the investigators will conduct field experiments in the Atlantic Ocean and perform a series of controlled laboratory studies with pure enzymes and microbial cultures to determine how and to what extent different DOP compounds are degraded to Pi in the marine environment. Furthermore, the contribution of these compound-specific DOP molecules to microbial P nutrition, carbon fixation, and community structure will be determined, thus advancing the current state of knowledge regarding the factors that control the activity and distribution of microbial species in the ocean, and the ocean?s role in the climate system. This project will support two female junior investigators, a postdoctoral researcher, and graduate and undergraduate students. The undergraduate students will be recruited from the Marine Sciences program at Savannah State University, an Historically Black Colleges and Universities. In addition, results will be incorporated into new hands-on K-12 educational tools to teach students about microbial P biogeochemistry, including a digital game and formal lesson plans with hands-on demos. These tools will be validated with K-12 educators and will be widely accessible to the public through various well-known online platforms. These activities will thus reach a broad audience including a significant fraction of underrepresented groups.P is a vital nutrient for life. Marine microorganisms utilize P-hydrolases, such as alkaline phosphatase (AP), to release and acquire phosphate (Pi) from a wide diversity of dissolved organic P (DOP) compounds, including P-esters (P-O-C bonds), phosphonates (P-C), and polyphosphates (P-O-P). Compound-specific DOP transformations have the potential to exert critical and wide-ranging impacts on marine microbial ecology (e.g. variable DOP bioavailability among species), biogeochemistry (e.g. P geologic sequestration via formation of calcium Pi), and global climate (e.g. aerobic production of the greenhouse gas methane by dephosphorylation of methylphosphonate). However, the mechanisms and comparative magnitude of specific DOP transformations, in addition to their relative contributions to microbial community-level P demand, productivity, and structure, are not completely understood. This study will fill these knowledge gaps by tracking the fate of specific DOP pools in the marine environment. Specifically, this project will test four hypotheses in the laboratory using recombinant enzymes and axenic cultures representative of marine eukaryotic and prokaryotic plankton from high and low nutrient environments, and in the field using observational and experimental approaches along natural Pi gradients in the Atlantic Ocean. In particular, the investigators will reveal potential differences in the hydrolysis and utilization of specific DOP compounds at the community- (bulk enzymatic assays), taxon- (cell sorting of radiolabeled cells in natural samples), species- (axenic cultures) and molecular-levels (pure enzyme kinetic studies and cell-associated proteomes and exoproteomes). Results from our proposed work will provide a robust understanding of the enzymatic basis involved in the transformation of specific forms of DOP and create new knowledge on the relative contribution of these specific P sources to Pi production, marine microbial nutrition, community structure, primary productivity, and thus global carbon cycling and climate. In particular, our refined measurements of the concentration of bioavailable DOP and our unique estimates of DOP remineralization fluxes will provide critical new information to improve models of marine primary production and P cycling.