Deciphering the Cryptic Cycling of Methane in Sediments of a Coastal Wetland

本研究以美国南加州海岸湿地为研究对象，探讨了无氧区沉积物中微生物对甲烷的产生和消耗之间的密切关系。这两个密切相关的微生物群体之间的甲烷直接交换，被称为“神秘的甲烷循环”，只是最近才被确定，很少有人知道它在减少沿海湿地甲烷排放方面的重要性。这项研究将揭示碳如何在两种类型的微生物之间移动，并将确定所涉及的微生物。 它还将揭示在不同环境条件下负责的重要代谢反应以及甲烷生产和消费之间的平衡。为了产生更广泛的影响，该项目将为两名本科生和一名研究生提供跨学科湿地科学和最先进的实验室方法方面的培训。 一门关于全球甲烷排放的新生课程将使本科生进入该领域，提供有关当地沿海湿地环境的教育。该项目的结果将传播给公众和学术团体，并将提供一个更好地了解甲烷的生产和消耗在沿海湿地。大气中的甲烷浓度比工业化前时代增加了一倍多，因此我们迫切需要了解控制这种强大的温室气体排放的机制。最近的研究首次证明了在富含有机质的沉积物的硫酸盐还原带中微生物同时产生和消耗甲烷，这一过程被称为“隐蔽甲烷循环”。“在这个过程中，甲烷被提议直接从甲基营养型甲烷生成到甲烷的厌氧氧化（AOM）。然而，人们对所涉及的生物体的身份、碳从一种代谢到另一种代谢的轨迹、或这两个过程的环境净结果知之甚少。没有这种代谢关系的细节，沉积物的甲烷预算仍然是不完整的。沿海湿地是特别感兴趣的隐式甲烷循环的研究，因为它们的有机和硫酸盐丰富的沉积物促进甲基营养型甲烷生成的甲基化底物的生产，并提供AOM的电子受体。然而，厌氧微生物从这个生态系统中去除甲烷，特别是沿着海洋和陆地之间的硫酸盐梯度，仍然没有得到很好的理解。对智力的优点，这项研究阐明了身份的产甲烷和甲烷古菌参与在沿海湿地的神秘甲烷循环，以及选择电子受体，燃料甲烷去除在这种代谢关系。这项研究提供了新的代谢线索，以揭示驱动甲烷生成和AOM的酶机制的多功能性。通过捕获控制这两个过程之间的平衡的环境因素，工作在很近的距离，这项工作的结果进一步提供了一个沿海湿地沉积物中的甲烷动力学的增强理解。这些信息可以应用于生物地球化学模型，以改善对该生态系统甲烷排放的预测，该生态系统遍布全球沿海地区。为了更广泛的影响，研究提供了创新的分析和实验技术的培训，两个本科生和一个研究生。该项目每年还邀请20名本科生参加新开发的新生研讨会，“甲烷-其他温室问题”，包括实地考察当地湿地。研讨会的目标是教育学生，包括那些没有进入STEM领域的学生，了解甲烷的全球来源和汇，以及它现在和未来在全球变暖中的作用。这项研究的结果将广泛传播到教育和公共宣传平台，如高中，社区学院和环境非营利组织，以教授科学方法，地球化学循环的概念，该奖项反映了NSF的法定使命，并通过利用基金会的知识价值和更广泛的影响进行评估，被认为值得支持审查标准。

This research project investigates the close relationship between methane production and consumption in sediments by microbes in the oxygen-free zone of a coastal wetland in Southern California. The direct exchange of methane between those two closely related microbial groups, which has been named "cryptic methane cycling", has only recently been identified and little is known about its importance in reducing methane emissions from coastal wetlands. This research will reveal how carbon moves between the two types of microbes, and will identify the microbes involved. It will also reveal the important metabolic reactions responsible and the balance between methane production and consumption under different environmental conditions. Towards broader impacts, this project will provide training for two undergraduate and one graduate student in interdisciplinary wetland science and state of the art laboratory methods. A new freshmen course on global methane emissions will bring undergraduate students into the field to provide education on local coastal wetland environments. Results of the project will be disseminated to public and academic groups and will provide a better understanding of methane production and consumption in coastal wetlands.Concentrations of atmospheric methane have more than doubled since the pre-industrial era, hence we urgently need to understand the mechanisms that control the emission of this potent greenhouse gas. Recent studies have provided the first evidence for the simultaneous microbial production and consumption of methane in the sulfate reduction zone of organic-rich sediments, a process named the "cryptic methane cycle." In this process, methane is proposed to be passed directly from methylotrophic methanogenesis to anaerobic oxidation of methane (AOM). However, little is known about the identity of the organisms involved, the trail of carbon from one metabolism to the other, or the environmental net result of the two processes. Without the details of this metabolic relationship, methane budgets of sediments remain incomplete. Coastal wetlands are of particular interest for the study of cryptic methane cycling, because their organic and sulfate rich sediments promote the production of methylated substrates for methylotrophic methanogenesis and provide electron acceptors for AOM. Yet, anaerobic microbial removal of methane from this ecosystem, particularly along the sulfate gradient between ocean and land, is still not well understood. Towards intellectual merit, this study elucidates the identity of methanogenic and methanotrophic archaea involved in cryptic methane cycling in a coastal wetland as well as the selection of electron acceptors that fuel methane removal in this metabolic relationship. The research provides new metabolic clues to unravel the versatility of the enzymatic machinery that drives methanogenesis and AOM. By capturing environmental factors that control the balance between the two processes working in close proximity, the results of this work further provide an enhanced understanding of methane dynamics in coastal wetland sediments. This information can be applied to biogeochemical models to improve the prediction of methane emissions from this ecosystem, which is found throughout the global coastal zone. Towards broader impacts, the research provides training in innovative analytical and experimental techniques to two undergraduate and one graduate student. The project further engages 20 undergraduates per year in a newly developed freshman seminar, "Methane - the Other Greenhouse Problem" including a field trip to the local wetland. The goal of the seminar will be to educate students, including those not entering STEM fields, about global sources and sinks of methane and its involvement in global warming now and in the future. Results of this study will be broadly disseminated to educational and public outreach platforms, such as high schools, community colleges, and environmental non-profits to teach scientific methodologies, concepts of biogeochemical cycling, and enhance the appreciation of this vital coastal environment.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.