Electromethanogenesis has emerged as a biological branch of Power-to-X technologies that implements methanogenic microorganisms, as an alternative to chemical Power-to-X, to convert electrical power from renewable sources, and CO into methane. Unlike biomethanation processes where CO is converted via exogenously added hydrogen, electromethanogenesis occurs in a bioelectrochemical set-up that combines electrodes and microorganisms. Thereby, mixed, or pure methanogenic cultures catalyze the reduction of CO to methane via reducing equivalents supplied by a cathode. Recent advances in electromethanogenesis have been driven by interdisciplinary research at the intersection of microbiology, electrochemistry, and engineering. Integrating the knowledge acquired from these areas is essential to address the specific challenges presented by this relatively young biotechnology, which include electron transfer limitations, low energy and product efficiencies, and reactor design to enable upscaling. This review approaches electromethanogenesis from a multidisciplinary perspective, putting emphasis on the extracellular electron uptake mechanisms that methanogens use to obtain energy from cathodes, since understanding these mechanisms is key to optimize the electrochemical conditions for the development of these systems. This work summarizes the direct and indirect extracellular electron uptake mechanisms that have been elucidated to date in methanogens, along with the ones that remain unsolved. As the study of microbial corrosion, a similar bioelectrochemical process with Fe as electron source, has contributed to elucidate different mechanisms on how methanogens use solid electron donors, insights from both fields, biocorrosion and electromethanogenesis, are combined. Based on the repertoire of mechanisms and their potential to convert CO to methane, we conclude that for future applications, electromethanogenesis should focus on the indirect mechanism with H as intermediary. By summarizing and linking the general aspects and challenges of this process, we hope that this review serves as a guide for researchers working on electromethanogenesis in different areas of expertise to overcome the current limitations and continue with the optimization of this promising interdisciplinary technology.

中文翻译：

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细胞外电子摄取机制与电产甲烷应用的相关性


电产甲烷作用已成为 Power-to-X 技术的一个生物分支，它利用产甲烷微生物作为化学 Power-to-X 的替代品，将可再生能源的电能和二氧化碳转化为甲烷。与通过外源添加的氢气转化二氧化碳的生物甲烷化过程不同，电产甲烷发生在结合电极和微生物的生物电化学装置中。因此，混合或纯产甲烷培养物通过阴极提供的还原当量催化CO还原为甲烷。微生物学、电化学和工程学交叉领域的跨学科研究推动了电产甲烷的最新进展。整合从这些领域获得的知识对于解决这种相对年轻的生物技术所带来的具体挑战至关重要，其中包括电子转移限制、低能量和产品效率以及用于扩大规模的反应器设计。本综述从多学科的角度探讨了电产甲烷作用，重点关注产甲烷菌从阴极获取能量的细胞外电子吸收机制，因为了解这些机制是优化这些系统开发的电化学条件的关键。这项工作总结了迄今为止在产甲烷菌中已阐明的直接和间接细胞外电子摄取机制，以及尚未解决的机制。微生物腐蚀是一种以 Fe 作为电子源的类似生物电化学过程，其研究有助于阐明产甲烷菌如何使用固体电子供体的不同机制，将生物腐蚀和电产甲烷这两个领域的见解结合起来。 根据机制的全部内容及其将二氧化碳转化为甲烷的潜力，我们得出结论，对于未来的应用，电产甲烷应侧重于以 H 作为中介的间接机制。通过总结和联系这一过程的一般方面和挑战，我们希望这篇综述能够为不同专业领域从事电产甲烷的研究人员提供指导，以克服当前的局限性，并继续优化这一有前途的跨学科技术。