Probing the cryptic nitrogen cycle

探索神秘的氮循环

• 批准号: NE/V007785/1
• 负责人: Mark Trimmer
• 金额: $ 10.06万
• 依托单位: Queen Mary University of London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FV007785%2F1
• 关键词: Probing; cryptic; nitrogen; cycle

The element nitrogen (N) is key to life - building proteins and the very DNA that tells life what to do. Nitrogen exists largely as di-nitrogen gas (N2) in the atmosphere, with a fraction being present in the organic N of life (humans, animals, plants, microbes etc.). Following death and decay, organic N decomposes to ammonia. The N in ammonia is then cycled back to the atmosphere through a coupling between microbes (microscopic organisms known as bacteria and archaea) that, on the one-hand, use oxygen to convert ammonia into nitrates and, on the other, microbes that respire nitrate in the absence of oxygen back to N2 gas. Oxygen rich, oxic-habitats are all around us, be it agricultural, grassland or forest soils or, indeed, your own back garden. If those soils become water logged, they will lose their oxygen and become anoxic-habitats and the same holds true for muddy sediments at the bottom of seas and lakes - and microbes in those anoxic habitats respire nitrates to N2 gas. This is the N cycle taught at school and although it has been updated in the past 20 years to include novel microbial pathways of producing N2 gas - the coupling between ammonia and N2 gas mediated through nitrates sits at its very heart.What's new? In 2016, Trimmer and his grouped published a paper showing that the division between the recognised oxic and anoxic parts of the N cycle was blurred, with ammonia being converted to N2 gas in clean, oxygen-rich gravel riverbeds. Subsequently, Trimmer had a PhD student continue to explore the N cycle in oxygen-rich gravel riverbeds. The opportunity now for a new international collaboration arouse fortuitously during the examination that PhD student by the external examiner Prof. Bo Thamdrup (University of Southern Denmark) who identified a mistake in an equation in Liao's thesis. Correcting this seemingly innocuous mistake turned out to have profound implications for our understanding of the N cycle; though not only in oxic riverbeds but in many other habitats that drive the Earth's N cycle. What has changed? Correcting the equation led to a new mathematical framework and placing our data into that new framework showed that the patterns in the N2 gas data - in the PhD thesis - disagreed with those expected for a coupling between distinct oxic and anoxic steps in the N cycle. Where that well-recognised coupling should include nitrates, our new mathematical framework argues for a cryptic-coupling that does not involve nitrates.Why does this matter? A cryptic-coupling not only changes our view of a fundamental step in the N cycle but - being hidden - a cryptic-coupling undoes 20 years' of research into the different microbial pathways that make N2 gas and our overall understanding of the N cycle is now challenged. Our new framework suggests a new pathway or at least a new type of coupling between known pathways in the N cycle that needs to be characterised before we can understand the cycling of a key bio-element on Earth. Further, unravelling this cryptic-coupling could facilitate the development of more efficient waste-water treatment i.e., by removing the need for separate oxic and anoxic treatment processes. We cannot, however, probe this new cryptic-coupling in the N cycle using current and widely available techniques - as they are simply blind to what it is we need to study. Hence, now in a new international collaboration we will pioneer the development of new tools to probe a cryptic-coupling in the N cycle. We will share complimentary mass-spectrometer facilities, along with contrasting field-sites and novel isotope and molecular techniques to deliver new fundamental and applied knowledge about the all too common, yet still enigmatic cycling of N on Earth.

氮元素（N）是构建生命的蛋白质的关键，也是告诉生命该做什么的DNA。氮在大气中主要以二氮气体（N2）的形式存在，其中一部分存在于生命（人类，动物，植物，微生物等）的有机氮中。死亡和腐烂后，有机氮分解成氨。氨中的氮然后通过微生物（称为细菌和古生菌的微生物）之间的耦合循环回到大气中，一方面，微生物使用氧气将氨转化为硝酸盐，另一方面，微生物在没有氧气的情况下将硝酸盐呼吸回N2气体。富氧、富氧的栖息地就在我们周围，无论是农业土壤、草原土壤还是森林土壤，甚至是你自己的后花园。如果这些土壤被水淹没，它们将失去氧气，成为缺氧的栖息地，海洋和湖泊底部的淤泥沉积物也是如此，这些缺氧栖息地的微生物将硝酸盐呼吸成N2气体。这是学校教授的氮循环，尽管在过去的20年里它已经更新，包括产生N2气体的新微生物途径-氨和N2气体之间通过硝酸盐介导的耦合位于其核心。2016年，Trimmer和他的团队发表了一篇论文，表明氮循环中公认的好氧和缺氧部分之间的界限是模糊的，氨在清洁、富氧的砾石河床中转化为N2气体。随后，Trimmer让一名博士生继续探索富氧砾石河床中的N循环。现在，一个新的国际合作的机会，在考试中偶然引起的博士生由外部考官教授博Thamdrup（南丹麦大学）谁发现了廖的论文中的一个方程的错误。纠正这个看似无害的错误对我们理解氮循环有着深远的影响;尽管不仅在含氧河床，而且在许多其他驱动地球氮循环的栖息地。什么改变了？校正方程导致了一个新的数学框架，并将我们的数据放入新的框架中，表明N2气体数据中的模式-在博士论文中-与N循环中不同的好氧和缺氧步骤之间的耦合预期不一致。在公认的耦合应该包括硝酸盐的地方，我们的新数学框架主张不涉及硝酸盐的神秘耦合。为什么这很重要？一个神秘的耦合不仅改变了我们对氮循环中一个基本步骤的看法，而且-隐藏-一个神秘的耦合破坏了20年来对制造N2气体的不同微生物途径的研究，我们对氮循环的整体理解现在受到了挑战。我们的新框架提出了一种新的途径，或者至少是N循环中已知途径之间的一种新型耦合，在我们了解地球上一种关键生物元素的循环之前，需要对其进行表征。此外，解开这种神秘的耦合可以促进更有效的废水处理的发展，即，通过消除对单独的好氧和缺氧处理过程的需要。然而，我们不能使用当前广泛可用的技术来探测N循环中的这种新的隐蔽耦合，因为它们对我们需要研究的东西是盲目的。因此，现在在一个新的国际合作中，我们将率先开发新的工具来探测N循环中的加密耦合。我们将分享免费的质谱仪设施，沿着对比现场和新的同位素和分子技术，以提供有关地球上N的所有常见但仍然神秘的循环的新的基础和应用知识。