Rewiring carbon flow in Synechocystis PCC 6803 for a high rate of CO2-to-ethanol under an atmospheric environment

E-Bin Gao; Junhua Wu; Penglin Ye; Haiyan Qiu; Huayou Chen; Zhen Fang

doi:10.3389/fmicb.2023.1211004

Rewiring carbon flow in Synechocystis PCC 6803 for a high rate of CO₂-to-ethanol under an atmospheric environment

Front Microbiol. 2023 May 31:14:1211004. doi: 10.3389/fmicb.2023.1211004. eCollection 2023.

Authors

E-Bin Gao^{1

2}, Junhua Wu³, Penglin Ye², Haiyan Qiu³, Huayou Chen¹, Zhen Fang²

Affiliations

¹ School of Life Sciences, Jiangsu University, Zhenjiang, Jiangsu, China.
² School of Environment and Safety Engineering, Jiangsu University, Zhenjiang, Jiangsu, China.
³ Ningbo Women and Children's Hospital, Ningbo, China.

Abstract

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 CO₂ to glycogen/biomass other than designed biofuels such as ethanol. Here, we used engineered Synechocystis sp. PCC 6803 to explore CO₂-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 CO₂. 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 CO₂.

Keywords: CO2 fixation; cofactor regeneration; cyanobacteria; metabolic engineering; photosynthetic cell factory.

Grants and funding

This work was supported by the National Natural Science Foundation of China (31200019), Ningbo Clinical Research Center for Children's Health and Diseases (2019A21002), Ningbo Top Medical and Health Research Program (No. 2022020405), Project of Faculty of Agricultural Equipment of Jiangsu University (NZXB20210203), and Young Talents Cultivation Program of Jiangsu University.