Nitrogen

氮通常是陆地生态系统的限制性营养物质。多种细菌和古细菌谱系已经进化出固定大气氮的能力，这对农艺系统来说是重要的投入。该反应由固氮酶进行，由三磷酸腺苷驱动。所有已知的固氮酶都被氧气抑制，导致特殊的适应，限制细胞内的游离氧水平。有一个例外：一种氧不敏感的固氮酶是从燃烧木炭的土壤中发现的一种自养链霉菌中分离出来的。这种依赖超氧化物的固氮酶具有部分特征，但该菌株已不再存在。本项目旨在重新分离原始菌株，并从类似环境中寻找其他耐O2的固氮菌株。然后，这些菌株将对其基因组进行测序，并研究其固氮酶的生化和生理特性，以了解它们的耐氧性，并促进它们向其他生物转移。在热自养链霉菌中发现耐氧超氧化物依赖固氮酶是一个引人注目的结果。它出现在教科书和评论中，但自1997年最初的描述以来，一直没有关于这一主题的主要出版物。关于为什么会这样，有很多猜测，也许最有可能的是，由于在一氧化碳环境中培养细胞的困难，有机体已经消失了。这种酶和/或其他类似氧不敏感的未知酶的重新发现，使这一项目成为一个高风险但高回报的项目。解开丢失的酶的谜团本身就是一项值得进行的智力工作。如果结果是阳性的，重新分离耐氧酶和/或发现其他例子，这将开辟重要的新研究途径。因此，这一温和的检测项目不仅可以引发对固氮酶主流思想的认真重新评估，而且还将改变生物固氮研究的主要方面。重新发现依赖超氧化物的固氮酶和/或发现新的耐氧固氮酶，以及随后对其进行遗传、生化、结构和生理特性的研究，是该项目的最终目标。我们将利用我们新的合作团队的互补专业知识和跨大西洋性质，该团队是在Niges‘Ideas Lab’组建的，将认真尝试这一大胆的努力。因此，这种高风险、高回报的项目非常适合这种类型的计划通话。如果成功，这项工作有可能改变固氮研究的所有领域，产生生物和工业副产品。特别是，这将是朝着未来目标迈出的第一步，即将耐氧固氮酶系统转移到农作物中，以可持续的方式减轻陆地氮素限制，而不会对环境造成负面影响。

Nitrogen is most often the limiting nutrient to terrestrial ecosystems. Multiple bacterialand archaeal lineages have evolved the ability to fix atmospheric nitrogen, representing significant inputs to agronomic systems. This reaction is carried out by nitrogenase and is driven by ATP. All known nitrogenases are inhibited by oxygen, leading to specialized adaptations that limit intracellular free oxygen levels. There is one exception: an oxygen insensitive nitrogenase has that was isolated from a Streptomyces thermoautotrophicus found in soil above burning charcoal fires. This superoxide-dependent nitrogenase was partially characterized but the strain is no longer available. The present project seeks to re-isolate the original strain, as well as seek other O2-tolerant nitrogen-fixing strains from similar environments. These strains will then have their genomes sequenced and the biochemical and physiological properties of their nitrogenases studied in order to understand the O2 tolerance and to facilitate their transfer to other organisms.The discovery of the oxygen-tolerant superoxide-dependent nitrogenase in Streptomyces thermoautotrophicus was a remarkable result. It features in textbooks and reviews and yet there have been no primary publications on the subject since the original description in 1997. There is a good deal of speculation on why this is case, perhaps the most likely is that organism has been lost because of the difficulty of culturing cells in a carbon monoxide atmosphere. The rediscovery of this enzyme and/or other unknown enzymes with similar oxygen-insensitivity, makes this a high-risk but high-reward project. Solving the mystery of the lost enzyme is in itself a worthwhileintellectual task. If the outcome is positive and the O2-tolerant enzyme is re-isolated and/or other examples are discovered, this will open up important new avenues of research. Thus, this modest detective project could not only trigger a serious reappraisal of mainstream thinking about nitrogenase but also would transform major aspects of biological nitrogen fixation research.The rediscovery of the superoxide dependent nitrogenase and/or the discovery ofnovel oxygen-tolerant nitrogenases, followed by their genetic, biochemical, structural, and physiological characterization, is the ultimate goal of this project. We shall exploit the complementary expertise and the transatlantic nature of our new collaborative team, which was assembled at the Nitrogen 'Ideas Lab', to make a serious attempt at this bold endeavor. This high risk, high reward project is thus well-suited to this type of program call. If successful, this work has the potential to transform all areas of nitrogen-fixation research with both biological and industrial spin-offs. In particular, this would represent the first step towards the future goal of moving oxygen-tolerant nitrogenase systems into crop plants to alleviate terrestrial nitrogen limitation in a sustainable manner without negative environmental consequences.