Zhou Jie, Meng Hengkai, Zhang Wei, Li Yin
CAS Key Laboratory of Microbial Physiological and Metabolic Engineering, State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
School of Life Sciences, University of Science and Technology of China, Hefei, China.
Adv Exp Med Biol. 2018;1080:97-116. doi: 10.1007/978-981-13-0854-3_5.
As photosynthetic prokaryotes, cyanobacteria can directly convert CO to organic compounds and grow rapidly using sunlight as the sole source of energy. The direct biosynthesis of chemicals from CO and sunlight in cyanobacteria is therefore theoretically more attractive than using glucose as carbon source in heterotrophic bacteria. To date, more than 20 different target chemicals have been synthesized from CO in cyanobacteria. However, the yield and productivity of the constructed strains is about 100-fold lower than what can be obtained using heterotrophic bacteria, and only a few products reached the gram level. The main bottleneck in optimizing cyanobacterial cell factories is the relative complexity of the metabolism of photoautotrophic bacteria. In heterotrophic bacteria, energy metabolism is integrated with the carbon metabolism, so that glucose can provide both energy and carbon for the synthesis of target chemicals. By contrast, the energy and carbon metabolism of cyanobacteria are separated. First, solar energy is converted into chemical energy and reducing power via the light reactions of photosynthesis. Subsequently, CO is reduced to organic compounds using this chemical energy and reducing power. Finally, the reduced CO provides the carbon source and chemical energy for the synthesis of target chemicals and cell growth. Consequently, the unique nature of the cyanobacterial energy and carbon metabolism determines the specific metabolic engineering strategies required for these organisms. In this chapter, we will describe the specific characteristics of cyanobacteria regarding their metabolism of carbon and energy, summarize and analyze the specific strategies for the production of chemicals in cyanobacteria, and propose metabolic engineering strategies which may be most suitable for cyanobacteria.
作为光合原核生物，蓝细菌可以直接将CO转化为有机化合物，并以阳光作为唯一能量来源快速生长。因此，在蓝细菌中利用CO和阳光直接生物合成化学品在理论上比在异养细菌中使用葡萄糖作为碳源更具吸引力。迄今为止，已经在蓝细菌中从CO合成了20多种不同的目标化学品。然而，构建菌株的产量和生产率比使用异养细菌所能获得的低约100倍，只有少数产品达到克级。优化蓝细菌细胞工厂的主要瓶颈是光合自养细菌代谢的相对复杂性。在异养细菌中，能量代谢与碳代谢整合在一起，因此葡萄糖可以为目标化学品的合成提供能量和碳。相比之下，蓝细菌的能量和碳代谢是分开的。首先，太阳能通过光合作用的光反应转化为化学能和还原力。随后，利用这种化学能和还原力将CO还原为有机化合物。最后，还原的CO为目标化学品的合成和细胞生长提供碳源和化学能。因此，蓝细菌能量和碳代谢的独特性质决定了这些生物体所需的特定代谢工程策略。在本章中，我们将描述蓝细菌在碳和能量代谢方面的具体特征，总结和分析蓝细菌中化学品生产的具体策略，并提出可能最适合蓝细菌的代谢工程策略。
