基于CO_(2)等碳一底物的化学品生物合成技术进展及挑战

Advances and perspectives of biosynthesis of chemicals based on CO_(2) and other one-carbon feedstocks

面对不断恶化的气候危机,开展二氧化碳的减排和资源化利用,向低碳和可持续发展模式转型已经迫在眉睫.其中大力发展绿色生物经济,开发高效的生物法固定二氧化碳和其衍生的碳一底物策略,并驱动化学品规模化生物制造,将发挥举足轻重的作用.本文围绕生物基化学品低碳合成,特别是以基于碳一化合物为原料的高附加值产品生物合成为重点,首先简要回顾了近几年相关领域的研究进展,包括提高自养微生物固碳效率、赋能大肠杆菌和酵母菌等异养微生物固碳效能、体外组装多酶体系进行固碳合成等;然后讨论了利用碳一化合物进行生物合成面临的科技挑战,包括固碳途径能量和还原力的消耗、较低的固碳效率与工业应用实际需求之间的巨大差异,并从工业应用角度讨论了混合底物及混合培养发酵的可行性.重点提出并探讨了聚焦甲醛为核心中间体的代谢途径的人工设计和优化策略,强调了甲醛在从无机碳到有机碳的转化以及碳链延长等方面的重要作用.作为能量供给及甲醛的来源之一,本文还介绍了电生物合成技术在低碳生物合成方面的潜力及面临的挑战.以1,3-丙二醇的生物合成为例,阐述了C1和C2以及电生物合成技术在这一重要大宗化学品生物合成中的应用途径.最后,讨论了从基础研究的0到1的原理突破进步到1到100的工业应用的挑战以及值得关注的核心科学和技术问题.

Global warming and climate change,mainly caused by the emission of carbon dioxide,is becoming a serious problem,and it is imperative to develop efficient capture and utilization technologies for carbon dioxide and its derivatives one-carbon(C1)compounds.The use of CO_(2) and other C1 compounds,such as formate,methanol and formaldehyde,for biomanufacturing of industrial chemicals is of great importance in the transition from a fossil-dependent economy to a green and sustainable bioeconomy.This review article mainly focuses on the biosynthesis of chemicals with the use of C1 compounds in the context of synthetic biology and discusses the challenges as well as potential solutions in this field.First,we briefly highlight the development of synthetic biology and its relation to biomanufacturing as well as the introduction of low-carbon biosynthesis concept,which includes low-carbon feedstocks,low-carbon bioproduction process and low-carbon industrial chain.With a focus on C1 feedstocks,we then summarize the latest research advances in enhancing the carbon fixation efficiency of autotrophic microorganisms,empowering heterotrophs such as Escherichia coli and yeast with carbon fixation capabilities,and assembling cell-free machineries in biomanufacturing.Furthermore,we present a comparison of 10 natural and artificial CO_(2)-fixation pathways,including their energy requirements and enzyme numbers in the corresponding pathway,which highlights the unique advantages of our recently developed integrated chemoenzymatic CO_(2) to amino-acid pathway(ICE-CAP)to turn CO_(2) into amino acids in a system without requirements for ATP/NAD(P)H and in only several steps.In the second part,we discuss the challenges faced in the chemical biosynthesis using C1 substrates,including the demand of high amounts of energy and reducing powers in carbon fixation pathways,low efficiency,low thermodynamic and kinetic driving forces of the pathway and the large gap between the practical needs of industrial applications and the currently limited capacity to use C1 compounds.As a promising solution,we presented the strategy to capture low-energy CO_(2) using the high-energy C1 compound methanol or formaldehyde in ICE-CAP to increase the energy utilization efficiencies.Furthermore,the low thermodynamic driving force in carbon-fixation pathways can be overcome by combining biocompatible chemistry(non-enzymatic)with enzymatic transformations.From the perspective of industrial applications,we illustrate the feasibilities of performing mixotrophic fermentation to enhancing the key parameters in terms of titer,yield and productivity in C1 utilization process for producing chemicals.Furthermore,we pay special attention to the key intermediate formaldehyde,which as an energyintensive C1 synthon is of high interest for biosynthesis,in C1 fixation and emphasize its pivotal role in the conversion of inorganic carbon to organic carbon and carbon-chain elongation.Different pathways and routes are summarized that involve formaldehyde as an intermediate or a starting point for biosynthesis.The toxicity of formaldehyde in principle can be overcome through adaptive laboratory evolution,enzyme engineering,compartmentalization of formaldehyde utilization and other means.Formaldehyde can be readily produced from methanol,formate,CO and CO_(2).As one of the power sources in producing formaldehyde,we introduce a concept of bioelectrochemically converting biogas(CO_(2) and CH_(4))into formaldehyde.In the third part,we take 1,3-propanediol(PDO)as an example to illustrate our efforts to produce this important chemical from C1 compounds.Finally,we discuss the need and challenges to move from the proof of concept(“0 to 1”)in fundamental research to the industrial application(“1 to 100”),as well as the key scientific and technical issues for future development.