Abstract:

CO₂ captures worldwide attention these days because of the urgent need to counteract its ever increasing in the atmosphere and its impact on climate change, with the ultimate goal of carbon neutrality. Recently, large efforts have been made in CO₂ capture and utilization, primarily using physical or chemical means. Biotechnological CO₂ capture and utilization has been mainly studied using microalgae, but turned out to be economically less competitive. Large-scale biotechnological capture and utilization of CO₂ thus urgently needs new concepts and technologies. The teams of Tan Tianwei and Jens Nielsen (Liu et al, 2020) recently reviewed the advances and challenges in biological CO₂ fixation in the context of third-generation (3G) biorefineries. The review gives an excellent survey and valuable discussions on sources of CO₂, the natural and synthetic CO₂ fixation pathways, use of regenerative energy, and 3G-based products. Perspectives of 3G biorefineries are also presented. It is clear that each CO₂ fixation pathway has its benefits and drawbacks and the choice depends on the microbial host, the target product(s), and the preferred process and cultivation conditions. In addition to the technical aspects, the authors also emphasized the necessity of further increasing social, political and economic incentives for continued financial support of research and small companies. This commentary briefly introduces the major points of the review of Liu et al. and discusses further aspects on the move from basic research to industrial application of CO₂ based biomanufacturing. In particular, we emphasize the following aspects: (1) More fundamental and quantitative studies on the underlying mechanisms of carbon binding and transformation to significantly increase the efficiency of key enzymes and metabolic modules of the different fixation pathways; (2) The interactions of CO₂ fixation pathway with metabolic network and their regulation deserve more systems level and quantitative study; (3) Integration of physical, chemical and electrochemical CO₂ capture and transformation methods with biological processes in the sense of biorefineries, also by considering the downstream processing of product recovery; (4) From the perspective of industrial application, autotrophic synthesis-based biomanufaturing has several major technological bottlenecks and economic constraints, mixotrophic biosynthesis (using CO₂ and mixed carbon sources) seems a practical solution and deserves more attention; (5) Finally, most of the CO₂ fixation pathways and their products are still at the proof of concept stage, engineering breakthroughs are urgently needed for moving from “0 to 1” to“1 to 100”and thus to really contribute to carbon neutrality.

Key words: third-generation (3G) biorefineries, carbon dioxide, fixation pathway, regenerative energy, synthetic biology, biomanufacturing

摘要：

在过去的几十年里，人们在二氧化碳（CO₂）捕获和利用方面做出了巨大的努力，但是通过生物技术大规模利用CO₂还缺乏市场竞争力，迫切需要新的方案和技术。谭天伟和Jens Nielsen的团队（刘子鹤等，2020）最近回顾了第三代（3G）生物炼制技术中生物固定CO₂方面的进展和挑战，对原材料、碳固定途径和所涉及的关键因素、能源供应和它们将二氧化碳同化为生物质的效率，以及随后基于3G的产品进行了出色的总结和探讨。该文还介绍了3G生物炼制的前景，指出了存在的挑战，并为未来的发展提供了前瞻性的建议。文章也讨论了整合多种碳固定途径和来自化学、生物和过程工程的技术以实现CO₂闭环固定和利用的机会和挑战。除了技术方面，文章还强调有必要进一步增加社会、政治和经济激励措施。本评论简要介绍刘子鹤等综述文章的主要内容，并进一步讨论了基于CO₂的生物制造从基础研究到工业应用的几个值得关注的问题：①在原子和分子水平上对碳碳键生成的机理进行更深入的基础和定量研究，以显著提高固碳途径的关键酶和代谢模块的效率；②在代谢途径及细胞水平上，对固碳反应与代谢网络的相互作用进行系统的定量研究；③在生物炼制的意义上，将物理、化学和电化学CO₂捕获和转化方法与生物过程相结合，同时考虑产品回收的下游处理；④从工业应用的角度来看，基于自养合成的生物制造存在多个技术瓶颈和经济限制，这些问题短期很难解决，混合营养生物合成（使用CO₂和混合碳源）是一个实用的解决方案；⑤大多数CO₂固定途径及其产品仍处于“概念验证”阶段，需要更多的工程研究来实现从“0到1”到“1到100”的技术需求，从而真正为碳中和做出贡献。

关键词: 第三代生物炼制, 二氧化碳, 生物同化途径, 可再生能源, 合成生物学, 生物制造