Gao E-Bin, Wu Junhua, Ye Penglin, Qiu Haiyan, Chen Huayou, Fang Zhen
School of Life Sciences, Jiangsu University, Zhenjiang, Jiangsu, China.
School of Environment and Safety Engineering, Jiangsu University, Zhenjiang, Jiangsu, China.
Front Microbiol. 2023 May 31;14:1211004. doi: 10.3389/fmicb.2023.1211004. eCollection 2023.
Cyanobacteria are an excellent microbial photosynthetic platform for sustainable carbon dioxide fixation. One bottleneck to limit its application is that the natural carbon flow pathway almost transfers CO to glycogen/biomass other than designed biofuels such as ethanol. Here, we used engineered sp. PCC 6803 to explore CO-to-ethanol potential under atmospheric environment. First, we investigated the effects of two heterologous genes (pyruvate decarboxylase and alcohol dehydrogenase) on ethanol biosynthesis and optimized their promoter. Furthermore, the main carbon flow of the ethanol pathway was strengthened by blocking glycogen storage and pyruvate-to-phosphoenolpyruvate backflow. To recycle carbon atoms that escaped from the tricarboxylic acid cycle, malate was artificially guided back into pyruvate, which also created NADPH balance and promoted acetaldehyde conversion into ethanol. Impressively, we achieved high-rate ethanol production (248 mg/L/day at early 4 days) by fixing atmospheric CO. Thus, this study exhibits the proof-of-concept that rewiring carbon flow strategies could provide an efficient cyanobacterial platform for sustainable biofuel production from atmospheric CO.
蓝细菌是用于可持续二氧化碳固定的优良微生物光合平台。限制其应用的一个瓶颈是，天然碳流途径几乎将二氧化碳转化为糖原/生物质，而非转化为乙醇等目标生物燃料。在此，我们利用工程化的集胞藻6803在大气环境下探索二氧化碳转化为乙醇的潜力。首先，我们研究了两个异源基因（丙酮酸脱羧酶和乙醇脱氢酶）对乙醇生物合成的影响，并优化了它们的启动子。此外，通过阻断糖原储存和丙酮酸到磷酸烯醇式丙酮酸的回流来强化乙醇途径的主要碳流。为了回收从三羧酸循环中逸出的碳原子，人为地将苹果酸引导回丙酮酸，这也创造了烟酰胺腺嘌呤二核苷酸磷酸（NADPH）平衡，并促进乙醛转化为乙醇。令人印象深刻的是，我们通过固定大气中的二氧化碳实现了高速率乙醇生产（在最初4天为248毫克/升/天）。因此，本研究展示了概念验证，即重新构建碳流策略可为从大气二氧化碳中可持续生产生物燃料提供一个高效的蓝细菌平台。
