Ethanol Metabolism Dynamics in Clostridium ljungdahlii Grown on Carbon Monoxide

Zi-Yong Liu; De-Chen Jia; Kun-Di Zhang; Hai-Feng Zhu; Quan Zhang; Wei-Hong Jiang; Yang Gu; Fu-Li Li

doi:10.1128/AEM.00730-20

Ethanol Metabolism Dynamics in Clostridium ljungdahlii Grown on Carbon Monoxide

Appl Environ Microbiol. 2020 Jul 2;86(14):e00730-20. doi: 10.1128/AEM.00730-20. Print 2020 Jul 2.

Authors

Zi-Yong Liu¹, De-Chen Jia², Kun-Di Zhang³, Hai-Feng Zhu¹, Quan Zhang⁴, Wei-Hong Jiang², Yang Gu⁵, Fu-Li Li⁶

Affiliations

¹ Shandong Provincial Key Laboratory of Synthetic Biology, Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, People's Republic of China.
² Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai, People's Republic of China.
³ State Key Laboratory of Microbial Technology, Shandong University, Qingdao, People's Republic of China.
⁴ Sinopec Dalian (Fushun) Research Institute of Petroleum and Petrochemicals, Dalian, People's Republic of China.
⁵ Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai, People's Republic of China Ygu02@sibs.ac.cn lifl@qibebt.ac.cn.
⁶ Shandong Provincial Key Laboratory of Synthetic Biology, Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, People's Republic of China Ygu02@sibs.ac.cn lifl@qibebt.ac.cn.

Abstract

Bioethanol production from syngas using acetogenic bacteria has attracted considerable attention in recent years. However, low ethanol yield is the biggest challenge that prevents the commercialization of syngas fermentation into biofuels using microbial catalysts. The present study demonstrated that ethanol metabolism plays an important role in recycling NADH/NAD⁺ during autotrophic growth. Deletion of bifunctional aldehyde/alcohol dehydrogenase (adhE) genes leads to significant growth deficiencies in gas fermentation. Using specific fermentation technology in which the gas pressure and pH were constantly controlled at 0.1 MPa and 6.0, respectively, we revealed that ethanol was formed during the exponential phase, closely accompanied by biomass production. Then, ethanol was oxidized to acetate via the aldehyde ferredoxin oxidoreductase pathway in Clostridium ljungdahlii A metabolic experiment using ¹³C-labeled ethanol and acetate, redox balance analysis, and comparative transcriptomic analysis demonstrated that ethanol production and reuse shared the metabolic pathway but occurred at different growth phases.IMPORTANCE Ethanol production from carbon monoxide (CO) as a carbon and energy source by Clostridium ljungdahlii and "Clostridium autoethanogenum" is currently being commercialized. During gas fermentation, ethanol synthesis is NADH-dependent. However, ethanol oxidation and its regulatory mechanism remain incompletely understood. Energy metabolism analysis demonstrated that reduced ferredoxin is the sole source of NADH formation by the Rnf-ATPase system, which provides ATP for cell growth during CO fermentation. Therefore, ethanol production is tightly linked to biomass production (ATP production). Clarification of the mechanism of ethanol oxidation and biosynthesis can provide an important reference for generating high-ethanol-yield strains of C. ljungdahlii in the future.

Keywords: CO fermentation; Clostridium ljungdahlii; acetate; acetogenesis; ethanol oxidation.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Autotrophic Processes
Biofuels / microbiology*
Carbon Monoxide / metabolism*
Clostridium / growth & development
Clostridium / metabolism*
Ethanol / metabolism*
Fermentation

Substances

Biofuels
Ethanol
Carbon Monoxide

Supplementary concepts

Clostridium ljungdahlii