In times of global climate change, the conversion and capturing of inorganic CO2 have gained increased attention because of its great potential as sustainable feedstock in the production of biofuels and biochemicals. CO2 is not only the substrate for the production of value-added chemicals in CO2-based bioprocesses, it can also be directly hydrated to formic acid, a so-called liquid organic hydrogen carrier (LOHC), by chemical and biological catalysts. Recently, a new group of enzymes were discovered in the two acetogenic bacteria Acetobacterium woodii and Thermoanaerobacter kivui which catalyze the direct hydrogenation of CO2 to formic acid with exceptional high rates, the hydrogen-dependent CO2 reductases (HDCRs). Since these enzymes are promising biocatalysts for the capturing of CO2 and the storage of molecular hydrogen in form of formic acid, we designed a whole-cell approach for T. kivui to take advantage of using whole cells from a thermophilic organism as H2/CO2 storage platform. Additionally, T. kivui cells were used as microbial cell factories for the production of formic acid from syngas. This study demonstrates the efficient whole-cell biocatalysis for the conversion of H2 + CO2 to formic acid in the presence of bicarbonate by T. kivui. Interestingly, the addition of KHCO3 not only stimulated formate formation dramatically but it also completely abolished unwanted side product formation (acetate) under these conditions and bicarbonate was shown to inhibit the membrane-bound ATP synthase. Cell suspensions reached specific formate production rates of 234 mmol gprotein−1 h−1 (152 mmol gCDW−1 h−1), the highest rates ever reported in closed-batch conditions. The volumetric formate production rate was 270 mmol L−1 h−1 at 4 mg mL−1. Additionally, this study is the first demonstration that syngas can be converted exclusively to formate using an acetogenic bacterium and high titers up to 130 mM of formate were reached. The thermophilic acetogenic bacterium T. kivui is an efficient biocatalyst which makes this organism a promising candidate for future biotechnological applications in hydrogen storage, CO2 capturing and syngas conversion to formate.

中文翻译：

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使用嗜热产乙酸的全细胞生物催化储氢和合成气转化为甲酸盐

在全球气候变化时期，无机二氧化碳的转化和捕集因其作为生物燃料和生物化学品生产中可持续原料的巨大潜力而​​受到越来越多的关注。CO2 不仅是在以 CO2 为基础的生物过程中生产增值化学品的基质，它还可以通过化学和生物催化剂直接水合为甲酸，即所谓的液态有机氢载体 (LOHC)。最近，在两种产酸细菌 Acetobacterium woodii 和 Thermoanaerobacter kivui 中发现了一组新的酶，它们以极高的速率催化 CO2 直接氢化成甲酸，即氢依赖性 CO2 还原酶 (HDCRs)。由于这些酶是用于捕获二氧化碳和以甲酸形式储存分子氢的有前途的生物催化剂，我们为 T. kivui 设计了一种全细胞方法，以利用来自嗜热生物的全细胞作为 H2/CO2 储存平台。此外，T. kivui 细胞被用作微生物细胞工厂，用于从合成气生产甲酸。本研究证明了在存在碳酸氢盐的情况下，T. kivui 对 H2 + CO2 转化为甲酸的高效全细胞生物催化。有趣的是，添加 KHCO3 不仅显着刺激了甲酸盐的形成，而且在这些条件下完全消除了不需要的副产物（乙酸盐）形成，并且碳酸氢盐被证明可以抑制膜结合的 ATP 合酶。细胞悬浮液达到了 234 mmol gprotein-1 h-1 (152 mmol gCDW-1 h-1) 的特定甲酸盐产生率，这是在封闭批次条件下报道的最高比率。在 4 mg mL-1 时，甲酸盐的体积产率为 270 mmol L-1 h-1。此外，这项研究首次证明合成气可以使用产乙酸细菌专门转化为甲酸盐，并且甲酸盐的滴度最高可达 130 mM。嗜热产乙酸细菌 T. kivui 是一种高效的生物催化剂，这使得该生物体成为未来在储氢、CO2 捕获和合成气转化为甲酸盐的生物技术应用的有希望的候选者。