Abstract:

CO₂ is both the primary greenhouse gas and an abundant carbon resource. Highly efficient CO₂ utilization technologies, which can alleviate the urgent pressure of energy and environment, are considered as the crucial reliances for getting the goal of “carbon peak and neutrality”. Photoautotrophic cyanobacteria can directly convert CO₂ into organic compounds only using solar energy. It is the main microbial chassis for developing light-driven cell factories that can produce useful compounds by capturing CO₂. As a typical representative of cyanobacteria, Synechococcus possesses many advantages: fast growth rate, clear genetic background, and low nutritional requirements. It is currently a hotspot of cyanobacterial synthetic biology. In the context of “carbon peak and neutrality,” research of Synechococcus chassis is ushering unprecedented opportunities. This review discusses the rationality and opportunities in developing cyanobacterial chassis from the perspectives of natural evolution, historical geologic limitations, climate dependence, and energy conversion efficiency. The application potentials in energy production, chemical manufacturing, and carbon sequestration are proposed and discussed. The metabolic potential of cyanobacteria is also discussed for their carbon fixation, light utilization, and biodiversity. Then, we systematically review the significant research advances in cyanobacterial chassis development and application. First, we describe the recently developed gene-editing methods of cyanobacteria, which are very important for constructing and remodeling cyanobacteria chassis. The feasibility of developing base editing technology that can facilitate multiplex editing in cyanobacteria is discussed. The CRISPRi technology for Synechococcus is also summarized. Second, we review the adaptive evolution in cyanobacteria. Researches on direct chassis evolution based on continuous cultivation and genetic element evolution based on phage and error-prone PCR are summarized. We also discuss the potential of adaptive evolution in cyanobacteria. Third, we review the stress tolerance of Synechococcus, especially the resistance to multiple stresses. The reported genetic elements responsible for stress factors, such as intense light, alkali, low pH, high temperature, and high salinity, are described. Some newly identified chassis are discussed on their unique characteristics. We propose some strategies for the directed engineering, which are practible for enhancing the stress tolerance of Synechococcus. Fourth, we review the progress of cyanobacterial cell factories and describe the recent production of various compounds by cyanobacteria, including bulk chemicals and fine chemicals. Moreover, we review new methods for developing cyanobacterial cell factories. The coculture method is discussed on its advantages and applications. The nanoparticle-mediated NADP regeneration is also reviewed for its application in enhancing the efficiency of the cyanobacterial cell factories. The existing problems and challenges are also listed with corresponding proposed solutions and coping strategies. We believe that the in-depth exploration of these problems and challenges will promote the advancement of cyanobacterial synthetic biology. It is expected that breakthroughs will soon be made in light energy capture, carbon fixation, stress resistance, and metabolic reprogramming. It is also expected that we can eventually design and build an efficient photosynthetic chassis surpassing natural evolution, based on which next-generation light-driven microbial factories can be constructed. This will significantly propel the realization of “carbon neutrality”.

Key words: Cyanobacteria, Synechococcus, synthetic biology, chassis cell, carbon neutrality, light-driven cell factory

摘要：

CO₂是最主要的温室气体，也是储量丰富的碳资源。发展CO₂的高效资源化利用技术可缓解迫切的能源和环境压力，是实现“双碳”目标的重要途径。蓝细菌可通过光合自养的方式将CO₂转变为有机物，是开发光驱动细胞工厂并直接利用CO₂生产化合物的主要微生物底盘。聚球藻作为蓝细菌的典型代表，生长快、遗传背景清楚、营养需求低，是目前光驱动合成生物学的热门底盘。在当前“碳达峰”和“碳中和”的“双碳”背景下，聚球藻底盘的研究正迎来前所未有的机遇。本文从自然进化、地球物理局限、土地气候依赖、太阳能转化效率等角度探讨了蓝细菌底盘开发的理性和机遇；分析了其在能源生产、化合物制造和碳汇与碳捕集中的应用潜力和愿景；从碳固定、光能捕捉和生物多样性的层面讨论了蓝细菌的代谢潜能。在上述基础上，系统综述了基因编辑、适应性进化、多元抗逆和光驱动细胞工厂这些蓝细菌合成生物学的热点研究领域近期的重要研究进展，并对当前所面临的挑战与难题进行了梳理，分析提出了可行的应对策略。对这些问题和挑战的深入探索有望推动光能捕获、固碳、抗逆、代谢网络重编等方面研究的突破，开发出超越自然进化的高效光合底盘，并最终建造高版本的光驱动细胞工厂，助力“双碳”目标的实现。

关键词: 蓝细菌, 聚球藻, 合成生物学, 底盘细胞, 碳中和, 光驱动细胞工厂