Abstract:

The increasing emission of CO₂ has resulted in severe climate problems, prompting global actions to reduce CO₂ emission or fix the atmospheric CO₂. In 2020, China set targets for carbon peaking and carbon neutrality, making it an urgent need to develop carbon-fixation technologies. Attributed to the rapid emergence of synthetic biology in recent years, CO₂ biotransformation through biochemical reactions catalyzed by enzymes and microbes has achieved a series of significant progress, in the design and engineering of enzymes, metabolic pathway, as well as the construction of in vitro/vivo systems. Many products, such as fuels, amino acids, starch, single-cell proteins, bio-based plastics, and other biocommodities, have been synthesized. Consequently, CO₂ is considered as the resource for third-generation biomanufacturing. The crucial step in CO₂ biotransformation is the activation of CO₂ molecules through the introduction of external energy. Compared to light, heat, and chemical energy, electrical energy is favored due to cost effectiveness, miniaturized apparatus, and convenience, attracting significant attention from both academia and industry. Electrical energy can be utilized in two ways for CO₂ biotransformation. In one way, CO₂ is electro-activated directly and biotransformed. In the other way, electrical energy facilitates the production of C1 intermediate such as formate, carbinol, CO, and the C₁ intermediates are then transformed by coupled microorganisms or enzymes, or the production of reducing forces such as NADH and H₂, which participate essentially in CO₂ biotransformation. This review comprehensively introduces research advancements in both approaches, analyzes potential carbon-fixation mechanisms, and discusses the advantages and disadvantages of different methods. Furthermore, the review proposes potential synthetic biology strategies to address efficiency concerns in CO₂ biotransformation, such as mining highly active carbon-fixing enzyme, enzyme engineering to improve the electron transfer efficiency between the enzyme and the electrode, metabolic engineering to enrich products of carbon-fixing microorganisms and improve the carbon-fixing efficiency, aiming to enable practical applications and the achievement of carbon neutrality goals.

Key words: CO₂ biotransformation, electrocatalysis, formate dehydrogenase, carbon monoxide dehydrogenase, carbon-fixing microbes

摘要：

CO₂排放带来全球性气候变化问题，为此世界各国纷纷采取了一系列减排固碳措施。我国于2020年提出“碳达峰，碳中和”发展目标，推进固碳技术发展迫在眉睫。受益于近年来合成生物学领域的迅猛发展，基于酶或微生物催化的CO₂生物转化研究在酶元件、途径和系统的人工设计改造等方面取得一系列重要进展，典型产物代表有燃料、氨基酸、淀粉、单细胞蛋白、生物塑料及其他多种生化产品。为此，CO₂也被认为是第三代生物原料。CO₂转化的关键在于外加能量活化CO₂分子，相比于光能、热能和化学能等，电能在成本投入和小型便捷方面优势突出，因此更受科学界和产业界青睐。CO₂生物转化利用电能分为两种方式，即生物直接利用电能固定CO₂和利用电能间接辅助CO₂生物转化［包括电催化CO₂还原、电再生辅因子（如NADH）、电解水制氢］。本文全面介绍了这两种方法在CO₂生物转化方面的研究进展，分析了可能的固碳机制，并讨论了不同方法的优点和缺点。此外，还提出了合成生物技术应对低效CO₂生物转化时的可能策略如挖掘高活性固碳酶、酶工程改造提高酶与电极之间的电子传递效率、代谢工程改造丰富固碳微生物的产物种类和提高固碳效率等，以期相关研究能真正走向实际应用，助力我国双碳目标的实现。

关键词: CO₂生物转化, 电催化, 甲酸脱氢酶, 一氧化碳脱氢酶, 固碳微生物