Collaborative Research: Manganese as a key reactant in the expanding low oxygen zones of the Gulf of Mexico, USA

合作研究：锰作为美国墨西哥湾不断扩大的低氧区域的关键反应物

• 批准号: 2023101
• 负责人: Emily Estes
• 金额: $ 31.39万
• 依托单位: Texas A&M University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2023101&HistoricalAwards=false
• 关键词: Collaborative; Research; Manganese; key; reactant

The Earth’s flow of energy – from animals, to plants, to microbes – is dictated by electron transfers, namely, moving electrons from one molecule or element to another to gain energy. Photosynthesis is perhaps the most familiar such reaction, where the electrons from carbon dioxide and water are used to make oxygen and sugar. However, before the appearance of oxygen-generating metabolisms, early life metabolism was governed by different electron transfer reactions – most of these involving metals because of their ability to readily donate and accept electrons. As a result of this early evolution, metals still play a central role in microbial life, as essential elements in enzymes. One such important metal is manganese (Mn), which is particularly good at donating and accepting electrons given that it can be in three different forms in the ocean. One form of Mn is a solid Mn-oxide, which is very reactive and almost as strong an oxidant as oxygen itself. This form of Mn is completely generated by bacteria, but we still know little about how bacteria do this, or why! One good place to understand these Mn reactions is in areas where oxygen is not present, because there, Mn reactions may dominate. The Gulf of Mexico is a region where oxygen concentrations have been decreasing steadily due to over-enrichment of nutrients from anthropogenic sources. This system is ideal for examining Mn reactions under low oxygen conditions, so in this project, how Mn reacts under different levels of oxygen will be determined. Scientists from the University of Rhode Island and Texas A&M University will also specifically target the bacteria that make these solid Mn oxides, to try and understand the mechanism of formation. Finally, the scientists will try to measure where the Mn is coming from and where it is going, to get a better idea of how Mn may undergo a complete reaction cycle. Understanding how metals cycle in the ocean is central to understanding life on Earth, as the inventory of metals has been subject to shifts in chemistry, like changing oxygen conditions, over the Earth’s history. A science communications student, an artist at sea, and a videographer will be incorporated into cruise activities to link the science with public outreach. This project will support three graduate students, undergraduate students, and two early career researchers. This project will focus on recruitment of underrepresented minorities to provide an introduction to STEM research and field work. At present, scientists from the University of Rhode Island and Texas A&M University have developed the chemical techniques to deconvolute manganese redox cycling in marine environments but have yet to thoroughly apply these new methods in diverse environmental systems or to couple manganese speciation and cycling with that of other elements. Here, the scientists propose to fully speciate manganese in the Gulf of Mexico, evaluating the formation, prevalence, and bioavailability of Mn(III)-L compounds and the role of microbes in facilitating Mn(III)-L and Mn oxide formation. In particular, the scientists seek to examine the stability of Mn(III)-L complexes across seasonal, salinity and oxygen gradients and to characterize both terrestrial and biotic Mn(III)-binding ligands. We hypothesize that Mn cycling, particularly in seasonally anoxic and suboxic zones, is intricately but enigmatically linked to the cycling of other redox sensitive species, including nitrogen and organic carbon compounds. This study will study these dynamics in the Gulf of Mexico, which has gradients in (1) productivity on a seasonal cycle, (2) salinity and terrestrial input via its tributaries and (3) a dynamic and seasonal oxygen regime. All of these gradients profoundly impact the redox chemistry of Mn and other elements and thus must be taken into account to create an accurate framework for understanding coupled redox cycling. In conducting this research, not only will we broadly elucidate the marine manganese cycling, we will also highlight previously cryptic chemical dynamics that drive the formation and dissipation of oxygen minimum zones in fragile coastal ecosystems.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.

地球的能量流——从动物到植物，再到微生物——是由电子转移决定的，即将电子从一个分子或元素转移到另一个分子或元素以获得能量，光合作用可能是最常见的此类反应，其中电子来自碳。然而，在产生氧气的代谢出现之前，涉及早期生命的代谢是由不同的电子转移反应控制的——大多数金属因为它们能够容易地提供和接受电子。由于这种早期进化，金属仍然在微生物生命中发挥着核心作用，锰 (Mn) 是一种重要的金属，由于它可以以三种不同的形式存在，因此它特别擅长提供和接受电子。锰的一种形式是固体锰氧化物，它具有很强的活性，几乎与氧气本身一样强，这种形式的锰完全由细菌产生，但我们对细菌如何做到这一点仍然知之甚少。 ， 或者为什么！了解这些锰反应的一个好地方是不存在氧气的区域，因为在墨西哥湾，由于人类活动造成的营养物质过度富集，锰反应可能占主导地位。该系统非常适合研究低氧条件下的锰反应，因此在该项目中，来自罗德岛大学和德克萨斯农工大学的科学家也将专门确定锰在不同氧气水平下的反应。使这些固体锰最后，科学家们将尝试测量锰的来源和去向，以更好地了解锰如何经历完整的反应循环。海洋中的金属循环对于了解地球上的生命至关重要，因为在地球的历史中，金属的库存一直受到化学变化的影响，例如氧气条件的变化。纳入邮轮活动，将科学与该项目将支持三名研究生、本科生和两名早期职业研究人员。该项目将重点招募来自罗德岛大学的科学家，以介绍 STEM 研究和实地工作。和德克萨斯农工大学已经开发出化学技术来解开海洋环境中锰的氧化还原循环，但尚未在不同的环境系统中彻底应用这些新方法，或将锰的形态和循环与其他元素的形态和循环结合起来。科学家们对墨西哥湾的形态锰进行了研究，评估了 Mn(III)-L 化合物的形成、普遍性和生物利用度，以及微生物在促进 Mn(III)-L 和锰氧化物形成中的作用。 Mn(III)-L 复合物在季节、盐度和氧气梯度上的稳定性，并表征陆地和生物 Mn(III) 结合配体，我们捕获了 Mn 循环，特别是在季节性中。缺氧和缺氧区域与其他氧化还原敏感物种（包括氮和有机碳化合物）的循环有着复杂但神秘的联系。这项研究将研究墨西哥湾的这些动态，该区域在季节性循环中存在（1）生产力梯度。 ，（2）通过其支流的盐度和陆地输入，以及（3）动态和季节性的氧气状况所有这些梯度都深刻地影响锰和其他元素的氧化还原化学，因此必须考虑到。创建一个准确的框架来理解耦合氧化还原循环。在进行这项研究时，我们不仅将广泛阐明海洋锰循环，还将强调以前神秘的化学动力学，这些化学动力学驱动脆弱的沿海生态系统中氧气最低区的形成和消散。授予 NSF 的法定使命，并通过评估反映使用基金会的智力优点和更广泛的影响审查标准，被认为值得支持。