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）由电子传输决定，即将电子从一个分子或元素移动到另一个分子，以获取能量。光合作用可能是最熟悉的反应，其中使用二氧化碳和水的电子制成氧气和糖。然而，在出现氧气代谢之前，早期生活代谢受不同的电子转移反应的控制 - 其中大多数涉及金属，因为它们可以轻松捐赠和接受电子产品。由于这种早期进化，金属仍然在微生物寿命中起着核心作用，作为酶的基本要素。一种如此重要的金属是锰（MN），它特别擅长捐赠和接受电子产品，因为它可以在海洋中以三种不同的形式捐赠。 MN的一种形式是一种固体Mn氧化物，它具有反应性，几乎与氧气一样强。这种MN的形式完全由细菌产生，但我们仍然对细菌的做法知之甚少，或者为什么！理解这些MN反应的一个好地方是不存在氧气的区域，因为那里的MN反应可能占主导地位。墨西哥湾是一个由于人为来源富集营养物质而静静地降低氧气浓度的区域。系统是在低氧气条件下检查MN反应的理想选择，因此在该项目中，将如何确定Mn在不同水平的氧气下反应。罗德岛大学和德克萨斯A＆M大学的科学家还将专门针对使这些固体MN氧化物的细菌，以尝试了解形成机理。最后，科学家将尝试测量MN的来源以及它的前进地点，以更好地了解MN如何经历完整的反应周期。了解金属在海洋中的循环是了解地球上生命的核心，因为金属的清单已经在化学的转变（如改变氧气状况）上发生了变化。科学传播专业的学生，​​海上艺术家和摄像师将被纳入巡航活动，以将科学与公共外展联系起来。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。该项目将着重于招募代表性不足的少数民族，以提供STEM研究和现场工作的介绍。目前，罗得岛大学和德克萨斯A＆M大学的科学家已经开发了化学技术来在海洋环境中摩根氧化还原循环，但尚未在潜水员环境系统中彻底应用这些新方法，或者将这些新方法应用于其他元素。在这里，科学家们建议在墨西哥湾完全特殊的锰，评估Mn（III）-L化合物的形成，流行和生物利用度以及微生物在促进MN（III）-L和MN氧化物形成的作用。特别是，科学家试图检查跨季节性，盐度和氧气梯度的Mn（III）-L络合物的稳定性，并表征陆生和生物Mn（III）结合配体的稳定性。我们假设MN循环，尤其是在季节性缺氧和子辅助区域中，与其他氧化还原敏感物种的循环（包括氮和有机碳化合物）的循环相关，但神秘地联系在一起。这项研究将研究墨西哥湾的这些动力学，该动力学在季节性周期的生产力中具有（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态。所有这些梯度都深刻影响了MN和其他元素的氧化还原化学，因此必须考虑到为理解耦合的氧化还原循环的准确框架。 In conducting this research, not only will we broadly elucidate the marine manganese cycling, we will also highlight previously cryptographic chemical dynamics that drive the formation and dissipation of oxygen minimum zones in fragile coastal ecosystems.This award reflects NSF's statutorial mission and has been deemed honestly of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.