Large Hydrogen Isotope Fractionation Distinguishes Nitrogenase-Derived Methane from Other Methane Sources
Large Hydrogen Isotope Fractionation Distinguishes Nitrogenase-Derived Methane from Other Methane Sources
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DOI：
10.1128/aem.00849-20
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发表时间：
2020-07
影响因子：
4.4
通讯作者：
K. Luxem;W. Leavitt;Xinning Zhang
中科院分区：
文献类型：
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作者：
K. Luxem;W. Leavitt;Xinning Zhang
所有的生命形式都需要氮来生长。生活在不同环境中的许多不同种类的微生物使用一种特殊的酶固氮酶使大气中的惰性氮气生物可用。固氮酶具有广泛的底物范围，并且除了产生生物可利用的氮之外，某些形式的固氮酶还产生少量的温室气体甲烷。这与其他产生甲烷以产生能量的微生物不同。到目前为止，还没有好的方法来确定具有固氮酶的微生物何时在自然界中制造甲烷。在这里，我们提出了一个同位素指纹，使科学家能够区分甲烷与微生物，使其成为能源与那些使其作为氮获取的副产品。有了这个新的指纹，就有可能提高我们对自然界中甲烷产生和氮获取之间关系的理解。生物固氮是由固氮酶催化的。这种金属酶的两种形式，钒（V）和铁（Fe）-唯一的固氮酶，最近被发现可以将少量的二氧化碳（CO2）还原为有效的温室气体甲烷（CH 4）。在这里，我们报告的碳（13 C/12 C）和氢（2 H/1 H）稳定同位素组成和分馏的V-和Fe-唯一的固氮酶在代谢上通用的固氮植物沼泽红球藻产生的甲烷。由两种形式的交替固氮酶赋予的稳定碳同位素分馏在氢营养产甲烷的观察范围内（V-固氮酶的13αCO2/CH 4 = 1.051 ± 0.002，仅Fe-固氮酶的13 α CO2/CH 4 = 1.055 ± 0.001;值为平均值±标准误差）。相比之下，氢同位素分馏（2αH2O/CH 4 = 2.071 ± 0.014的V-固氮酶和2.078 ± 0.018的Fe-唯一固氮酶）是任何已知的生物或地质途径中最大的。大的2αH2O/CH 4表明固氮酶用于形成甲烷的反应途径强烈地区别于2 H，并且2αH2O/CH 4将固氮酶衍生的甲烷与所有其他已知的生物和非生物来源区分开来。这些关于固氮酶衍生甲烷的发现将有助于限制微生物群落中的碳和氮流动以及替代固氮酶在全球生物地球化学循环中的作用。所有的生命形式都需要氮来生长。生活在不同环境中的许多不同种类的微生物使用一种特殊的酶固氮酶使大气中的惰性氮气生物可用。固氮酶具有广泛的底物范围，并且除了产生生物可利用的氮之外，某些形式的固氮酶还产生少量的温室气体甲烷。这与其他产生甲烷以产生能量的微生物不同。到目前为止，还没有好的方法来确定具有固氮酶的微生物何时在自然界中制造甲烷。在这里，我们提出了一个同位素指纹，使科学家能够区分甲烷与微生物，使其成为能源与那些使其作为氮获取的副产品。有了这个新的指纹，就有可能提高我们对自然界中甲烷产生和氮获取之间关系的理解。
All forms of life require nitrogen for growth. Many different kinds of microbes living in diverse environments make inert nitrogen gas from the atmosphere bioavailable using a special enzyme, nitrogenase. Nitrogenase has a wide substrate range, and, in addition to producing bioavailable nitrogen, some forms of nitrogenase also produce small amounts of the greenhouse gas methane. This is different from other microbes that produce methane to generate energy. Until now, there was no good way to determine when microbes with nitrogenases are making methane in nature. Here, we present an isotopic fingerprint that allows scientists to distinguish methane from microbes making it for energy versus those making it as a by-product of nitrogen acquisition. With this new fingerprint, it will be possible to improve our understanding of the relationship between methane production and nitrogen acquisition in nature. ABSTRACT Biological nitrogen fixation is catalyzed by the enzyme nitrogenase. Two forms of this metalloenzyme, the vanadium (V)- and iron (Fe)-only nitrogenases, were recently found to reduce small amounts of carbon dioxide (CO2) into the potent greenhouse gas methane (CH4). Here, we report carbon (13C/12C) and hydrogen (2H/1H) stable isotopic compositions and fractionations of methane generated by V- and Fe-only nitrogenases in the metabolically versatile nitrogen fixer Rhodopseudomonas palustris. The stable carbon isotope fractionation imparted by both forms of alternative nitrogenase are within the range observed for hydrogenotrophic methanogenesis (13αCO2/CH4 = 1.051 ± 0.002 for V-nitrogenase and 1.055 ± 0.001 for Fe-only nitrogenase; values are means ± standard errors). In contrast, the hydrogen isotope fractionations (2αH2O/CH4 = 2.071 ± 0.014 for V-nitrogenase and 2.078 ± 0.018 for Fe-only nitrogenase) are the largest of any known biogenic or geogenic pathway. The large 2αH2O/CH4 shows that the reaction pathway nitrogenases use to form methane strongly discriminates against 2H, and that 2αH2O/CH4 distinguishes nitrogenase-derived methane from all other known biotic and abiotic sources. These findings on nitrogenase-derived methane will help constrain carbon and nitrogen flows in microbial communities and the role of the alternative nitrogenases in global biogeochemical cycles. IMPORTANCE All forms of life require nitrogen for growth. Many different kinds of microbes living in diverse environments make inert nitrogen gas from the atmosphere bioavailable using a special enzyme, nitrogenase. Nitrogenase has a wide substrate range, and, in addition to producing bioavailable nitrogen, some forms of nitrogenase also produce small amounts of the greenhouse gas methane. This is different from other microbes that produce methane to generate energy. Until now, there was no good way to determine when microbes with nitrogenases are making methane in nature. Here, we present an isotopic fingerprint that allows scientists to distinguish methane from microbes making it for energy versus those making it as a by-product of nitrogen acquisition. With this new fingerprint, it will be possible to improve our understanding of the relationship between methane production and nitrogen acquisition in nature.