Connections between the Marine Biogeochemistry of Cobalt and Vitamin B12

维生素B12（钴胺素）是一种含钴的生物分子，在海水中含量极低。海洋环境中的许多真核浮游植物都需要它，因此它是一种重要的微量营养素。钴元素也是海洋环境中蓝细菌和真核浮游植物的重要微量营养素，而且浓度极低。由于维生素B12在其环状结构的中心含有一个钴原子，这些微量营养素的生物化学必须相互关联。近年来，我们观察到钴和铁对热带环境的共模拟，以及B 12和铁对极地沃茨的共模拟。此外，钴的生物利用度似乎受到结合钴的天然有机配体的强烈控制。然而，使用环境海水钴生物合成B12是一个重要且未研究的过程。该提案描述了一种策略，以阐明这两种微量营养素，钴和B12之间的联系，通过分析和生理研究测量关键的化学和生物参数。在这项研究中，伍兹霍尔海洋研究所计划的一个研究小组将测试以下假设：--虽然维生素B12中发现的钴只是海水中溶解钴总量的一小部分，但维生素B12的地球化学对钴的地球化学循环产生重大影响。 B12的光解产生降解产物，这些降解产物是海水中强钴配体的重要来源，这些配体在水柱中主导钴化学和生物利用度。 --原绿球藻和聚球藻等海洋蓝藻在海洋表层非常丰富，是海洋初级生产力中B12的主要来源。 - 原生动物的摄食和这些蓝藻种群的病毒裂解是将B12释放到海水中的有效手段。这些假设将通过一系列精心协调的实验进行测试，这些实验采用了灵敏的分析技术（伏安法、ICP-MS、LC-MS、UV-VIS光谱法）。这些实验将包括：1）B12降解产物（光解）的热力学结合常数和结构特征，并假设它们可能是海洋环境中CoL的主要来源。2)海洋蓝细菌（聚球藻和原绿球藻）的B12生产率。3)B12从放牧和病毒引起的蓝藻死亡率的释放率。总之，研究小组希望在理解这两种微量营养素之间的相互联系方面取得重大进展。有一些更广泛的影响。 该项目将为两名二年级化学海洋学学生Erin Bertrand和Abigail Noble提供培训。它还应提供对钴和维生素B12的生物地球化学的重要见解，这两种微量营养素都可以影响海洋初级生产力和海洋碳循环。这项研究也与研究微量元素和同位素的GEOTRACES计划高度相关和协同。最后，由于维生素是众所周知的公众，PI将继续使用这个主题作为一种手段，激发公众对海洋科学在当地的课堂演示和流行的文章。

Vitamin B12 (cobalamine) is a cobalt containing biomolecule found in exceedingly low quantities in seawater. It is required for use by many eukaryotic phytoplankton in the marine environment and hence is an important micronutrient. The element cobalt is also an important micronutrient to both cyanobacteria and eukaryotic phytoplankton in the marine environment and also is found in extremely low concentrations. Because vitamin B12 contains a cobalt atom in the center of its ring structure, the biogeochemistry of these micronutrients must be interconnected. In recent years we have observed colimitation of tropical environments by cobalt and iron, and colimitation of polar waters by B12 and Fe. In addition, the bioavailability of cobalt appears to be strongly controlled by natural organic ligands that bind cobalt. Yet, the biosynthesis of B12 using ambient seawater cobalt is an important and unstudied process. This proposal describes a strategy to elucidate the connections between these two micronutrients, Co and B12, by analytical and physiological studies measuring key chemical and biological parameters. In this study, a research team at the Woods Hole Oceanographic Institution plan will test the following hypotheses: -- While the cobalt found in vitamin B12 is only a small fraction of the total dissolved cobalt in seawater, vitamin B12 biogeochemistry exerts a major influence on the cobalt biogeochemical cycle. -- Photolysis of B12 results in degradation products that are an important source of the strong cobalt ligands in seawater that dominate cobalt chemistry and bioavailability in the water column. -- The marine cyanobacteria, such as Prochlorococcus and Synechococcus, are so abundant in the surface oceans that they are a major source of B12 to marine primary productivity. -- Protozoan grazing and viral lysis of these cyanobacteria populations are effective means to release B12 into seawater. These hypotheses will be tested through a carefully coordinated set of experiments utilizing sensitive analytical techniques (voltammetry, ICP-MS, LC-MS, UV-VIS spectroscopy). These experiments will include: 1) Thermodynamic binding constants and structural characteristics of the B12 degradation products (photolysis), with the hypothesis that they may be the major source of CoL in the marine environment. 2) Production rates of B12 by marine cyanobacteria (Synechococcus and Prochlorococcus, specifically). 3) Release rates of B12 from grazing and viral induced cyanobacterial mortality. In summary, the research team expects to make significant progress in understanding the interconnections between these two micronutrients. There are a number of broader impacts. The project will provide training for two second-year chemical oceanography students, Erin Bertrand and Abigail Noble. It should also provide important insights into the biogeochemistry of cobalt and vitamin B12, both of which are micronutrients that can influence marine primary productivity and the marine carbon cycle. This research is also highly relevant and synergistic with the GEOTRACES program studying trace elements and isotopes. Finally, because vitamins are well known to the public, the PI will continue to use this topic as a means to excite the public about marine science in local classroom presentations and popular articles.