Pathogenic microorganisms use various mechanisms to conserve energy in host tissues and environmental reservoirs. One widespread but often overlooked means of energy conservation is through the consumption or production of molecular hydrogen (H2). Here, we comprehensively review the distribution, biochemistry, and physiology of H2 metabolism in pathogens. Over 200 pathogens and pathobionts carry genes for hydrogenases, the enzymes responsible for H2 oxidation and/or production. Furthermore, at least 46 of these species have been experimentally shown to consume or produce H2 Several major human pathogens use the large amounts of H2 produced by colonic microbiota as an energy source for aerobic or anaerobic respiration. This process has been shown to be critical for growth and virulence of the gastrointestinal bacteria Salmonella enterica serovar Typhimurium, Campylobacter jejuni, Campylobacter concisus, and Helicobacter pylori (including carcinogenic strains). H2 oxidation is generally a facultative trait controlled by central regulators in response to energy and oxidant availability. Other bacterial and protist pathogens produce H2 as a diffusible end product of fermentation processes. These include facultative anaerobes such as Escherichia coli, S Typhimurium, and Giardia intestinalis, which persist by fermentation when limited for respiratory electron acceptors, as well as obligate anaerobes, such as Clostridium perfringens, Clostridioides difficile, and Trichomonas vaginalis, that produce large amounts of H2 during growth. Overall, there is a rich literature on hydrogenases in growth, survival, and virulence in some pathogens. However, we lack a detailed understanding of H2 metabolism in most pathogens, especially obligately anaerobic bacteria, as well as a holistic understanding of gastrointestinal H2 transactions overall. Based on these findings, we also evaluate H2 metabolism as a possible target for drug development or other therapies.

中文翻译：

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分子氢代谢：病原细菌和原生生物的广泛特征。

病原微生物利用各种机制在宿主组织和环境储存库中保存能量。一种广泛但经常被忽视的节能方法是通过消耗或生产分子氢 (H2)。在这里，我们全面回顾了病原体中 H2 代谢的分布、生物化学和生理学。超过 200 种病原体和病原体携带氢化酶基因，氢化酶负责 H2 氧化和/或产生。此外，实验表明其中至少有 46 个物种能够消耗或产生 H2。几种主要的人类病原体利用结肠微生物群产生的大量 H2 作为有氧或无氧呼吸的能源。该过程已被证明对于胃肠道细菌鼠伤寒沙门氏菌、空肠弯曲杆菌、简洁弯曲杆菌和幽门螺杆菌（包括致癌菌株）的生长和毒力至关重要。H2 氧化通常是一种兼性特征，由中央调节器控制，以响应能量和氧化剂的可用性。其他细菌和原生生物病原体产生的氢气是发酵过程中可扩散的最终产物。其中包括兼性厌氧菌，如大肠杆菌、鼠伤寒沙门氏菌和贾第鞭毛虫，当呼吸电子受体受到限制时，它们会通过发酵而持续存在；还包括专性厌氧菌，如产气荚膜梭菌、艰难梭菌和阴道毛滴虫，它们会产生大量的生长期间的H2。总体而言，关于氢化酶在某些病原体的生长、存活和毒力中的作用有丰富的文献。然而，我们缺乏对大多数病原体（尤其是专性厌氧菌）的 H2 代谢的详细了解，也缺乏对胃肠道 H2 交易的整体了解。基于这些发现，我们还评估 H2 代谢作为药物开发或其他疗法的可能目标。