Domestication of CO2-fixation became a worldwide priority enhanced by the will to convert this greenhouse gas into fuels and valuable chemicals. Because of its high stability, CO2-activation/fixation represents a true challenge for chemists. Autotrophic microbial communities, however, perform these reactions under standard temperature and pressure. Recent discoveries shine light on autotrophic acetogenic bacteria and hydrogenotrophic methanogens, as these anaerobes use a particularly efficient CO2-capture system to fulfill their carbon and energy needs. While other autotrophs assimilate CO2 via carboxylation followed by a reduction, acetogens and methanogens do the opposite. They first generate formate and CO by CO2-reduction, which are subsequently fixed to funnel the carbon toward their central metabolism. Yet their CO2-reduction pathways, with acetate or methane as end-products, constrain them to thrive at the "thermodynamic limits of Life". Despite this energy restriction acetogens and methanogens are growing at unexpected fast rates. To overcome the thermodynamic barrier of CO2-reduction they apply different ingenious chemical tricks such as the use of flavin-based electron-bifurcation or coupled reactions. This mini-review summarizes the current knowledge gathered on the CO2-fixation strategies among acetogens. While extensive biochemical characterization of the acetogenic formate-generating machineries has been done, there is no structural data available. Based on their shared mechanistic similarities, we apply the structural information obtained from hydrogenotrophic methanogens to highlight common features, as well as the specific differences of their CO2-fixation systems. We discuss the consequences of their CO2-reduction strategies on the evolution of Life, their wide distribution and their impact in biotechnological applications.

中文翻译：

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能量极端微生物中的CO2固定策略：我们可以从产乙酸素中学到什么？

通过将这种温室气体转化为燃料和有价值的化学物质的意愿，固定二氧化碳的驯化已成为世界范围内的优先事项。由于其高稳定性，CO2活化/固定代表了化学家的真正挑战。然而，自养微生物群落在标准温度和压力下进行这些反应。最近的发现为自养产乙酸细菌和氢养产甲烷菌大放光彩，因为这些厌氧菌使用特别有效的二氧化碳捕获系统来满足其碳和能源需求。尽管其他自养生物通过羧化作用随后被还原来吸收二氧化碳，但是产乙酸菌和产甲烷菌却相反。他们首先通过还原CO2生成甲酸盐和一氧化碳，然后将其固定以将碳汇聚到它们的中央代谢中。但是他们的二氧化碳减排途径 以乙酸盐或甲烷为最终产物，限制它们在“生命的热力学极限”下蓬勃发展。尽管有这样的能量限制，但是乙酸原和甲烷原以惊人的快速速度增长。为了克服减少CO2的热力学障碍，他们应用了各种巧妙的化学技巧，例如使用基于黄素的电子分叉或偶联反应。这份小型回顾总结了当前有关乙酸原固定二氧化碳策略的知识。虽然已经对产乙酸的甲酸生成机械进行了广泛的生化表征，但是尚无可用的结构数据。基于它们共同的机理相似性，我们应用从氢营养型产甲烷菌中获得的结构信息来突出其共同特征，以及其二氧化碳固定系统的具体差异。我们讨论了二氧化碳减排策略对生命进化，其广泛分布及其对生物技术应用的影响的后果。