Formate-Dependent Heterodisulfide Reduction in a Methanomicrobiales Archaeon
Formate-Dependent Heterodisulfide Reduction in a Methanomicrobiales Archaeon
复制标题
甲烷微生物古菌中依赖甲酸盐的异二硫键还原
DOI：
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发表时间：
2020
影响因子：
4.4
通讯作者：
K. Costa
中科院分区：
文献类型：
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作者：
M. A. Abdul Halim;L. Day;K. Costa
来自甲烷微生物目的产甲烷菌被认为偏好H2作为生长的电子供体。它们普遍存在于厌氧环境中，如废水处理设施、厌氧消化器和瘤胃，在那里它们催化有机物分解的最终步骤。摘要氢营养型产甲烷菌利用H2作为电子供体还原CO2产生CH4。在不存在H2的情况下，许多能够使用甲酸盐或醇作为替代电子供体。来自甲烷微生物目的产甲烷菌能够与H2一起生长，但许多缺乏编码氢化酶的基因，所述氢化酶通常存在于其他氢营养产甲烷菌中。为了更好地了解甲烷微生物目产甲烷菌中的电子流，我们对嗜热甲烷菌中的异二硫键还原酶（Hdr）进行了遗传和生化研究。Hdr通过基于黄素的电子分叉耦合甲烷生成的第一步和最后一步来催化一个重要的反应。从M.嗜热菌与甲酸脱氢酶（Fdh）共纯化，并且仅在甲酸作为电子供体时显示活性。我们没有发现Hdr相关氢化酶的证据，H2不能作为电子供体，即使H2上生长的细胞纯化Hdr。我们发现细胞催化甲酸氢解酶活性，这可能是生成Hdr反应所需的甲酸所必需的。总之，这些结果突出了甲酸盐作为产甲烷的电子供体的重要性，并表明使用甲酸盐的能力被紧密地整合到来自甲烷微生物目的生物体中的产甲烷途径中。重要性来自甲烷微生物目的产甲烷菌被认为更喜欢H2作为生长的电子供体。它们普遍存在于厌氧环境中，如废水处理设施、厌氧消化器和瘤胃，在那里它们催化有机物分解的最终步骤。然而，尽管它们的重要性，这些生物体的代谢仍然研究不足。利用遗传和生物化学的方法，我们表明，甲酸代谢是紧密结合到甲烷产甲烷嗜热菌。这是由于需要甲酸盐作为杂二硫还原酶（Hdr）的电子供体，Hdr是一种负责通过将初始CO2固定步骤连接到途径的放能末端反应来催化甲烷生成中的基本反应的酶。这些结果表明，氢不一定是所有氢营养产甲烷菌的首选电子供体，并提供洞察甲烷微生物目产甲烷菌的代谢。
Methanogens from the order Methanomicrobiales are thought to prefer H2 as an electron donor for growth. They are ubiquitous in anaerobic environments, such as in wastewater treatment facilities, anaerobic digesters, and the rumen, where they catalyze the terminal steps in the breakdown of organic matter. ABSTRACT Hydrogenotrophic methanogens produce CH4 using H2 as an electron donor to reduce CO2. In the absence of H2, many are able to use formate or alcohols as alternate electron donors. Methanogens from the order Methanomicrobiales are capable of growth with H2, but many lack genes encoding hydrogenases that are typically found in other hydrogenotrophic methanogens. In an effort to better understand electron flow in methanogens from the Methanomicrobiales, we undertook a genetic and biochemical study of heterodisulfide reductase (Hdr) in Methanoculleus thermophilus. Hdr catalyzes an essential reaction by coupling the first and last steps of methanogenesis through flavin-based electron bifurcation. Hdr from M. thermophilus copurified with formate dehydrogenase (Fdh) and only displayed activity when formate was supplied as an electron donor. We found no evidence of an Hdr-associated hydrogenase, and H2 could not function as an electron donor, even with Hdr purified from cells grown on H2. We found that cells catalyze a formate hydrogenlyase activity that is likely essential for generating the formate needed for the Hdr reaction. Together, these results highlight the importance of formate as an electron donor for methanogenesis and suggest the ability to use formate is closely integrated into the methanogenic pathway in organisms from the order Methanomicrobiales. IMPORTANCE Methanogens from the order Methanomicrobiales are thought to prefer H2 as an electron donor for growth. They are ubiquitous in anaerobic environments, such as in wastewater treatment facilities, anaerobic digesters, and the rumen, where they catalyze the terminal steps in the breakdown of organic matter. However, despite their importance, the metabolism of these organisms remains understudied. Using a genetic and biochemical approach, we show that formate metabolism is closely integrated into methanogenesis in Methanoculleus thermophilus. This is due to a requirement for formate as the electron donor to heterodisulfide reductase (Hdr), an enzyme responsible for catalyzing essential reactions in methanogenesis by linking the initial CO2 fixing step to the exergonic terminal reaction of the pathway. These results suggest that hydrogen is not necessarily the preferred electron donor for all hydrogenotrophic methanogens and provide insight into the metabolism of methanogens from the order Methanomicrobiales.