Data for Formate dependent heterodisulfide reduction in a Methanomicrobiales archaeon

Hydrogenotrophic methanogens produce CH4 using H2 as 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 co-purified 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.

氢营养型产甲烷菌（Hydrogenotrophic methanogens）利用H₂作为电子供体还原CO₂以产生CH₄。在缺乏H₂的条件下，许多此类菌体能利用甲酸或醇类作为替代电子供体。产甲烷微菌目（Methanomicrobiales）的产甲烷菌能够利用H₂生长，但许多菌株缺乏编码氢化酶（hydrogenases）的基因——这类基因在其他氢营养型产甲烷菌中普遍存在。为了更好地理解产甲烷微菌目产甲烷菌中的电子流机制，我们对嗜热甲烷袋状菌（Methanoculleus thermophilus）中的异二硫键还原酶（heterodisulfide reductase, Hdr）开展了遗传学与生物化学研究。Hdr通过基于黄素的电子分叉（flavin-based electron bifurcation）将产甲烷过程的第一步与最后一步偶联，催化关键反应。来自嗜热甲烷袋状菌的Hdr与甲酸脱氢酶（formate dehydrogenase, Fdh）共纯化，且仅在提供甲酸作为电子供体时才表现出活性。我们未发现Hdr相关氢化酶存在的证据，且即便使用从H₂培养的细胞中纯化得到的Hdr，H₂也无法作为其电子供体发挥作用。我们还发现，菌体具有甲酸氢解酶（formate hydrogenlyase）活性，这一活性可能对生成Hdr反应所需的甲酸至关重要。综合这些结果可知，甲酸作为产甲烷过程电子供体的作用十分关键，且产甲烷微菌目微生物利用甲酸的能力与其产甲烷途径紧密整合。