Metabolic engineering of Clostridium acetobutylicum for butyric acid production with high butyric acid selectivity |
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| Affiliation: | 1. Metabolic and Biomolecular Engineering National Research Laboratory, Department of Chemical and Biomolecular Engineering (BK21 plus program), BioProcess Engineering Research Center, KAIST, Daejeon 305-701, Republic of Korea;2. Center for Systems and Synthetic Biotechnology, Institute for the BioCentury, KAIST, Daejeon 305-701, Republic of Korea;3. Department of Bio and Brain Engineering and Bioinformatics Research Center, KAIST, Daejeon 305-701, Republic of Korea;1. School of Bioscience & Bioengineering, South China University of Technology, Guangzhou 510006, PR China;2. William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH 43210, USA;3. Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210, USA;1. State Key Laboratory of Microbial Technology, School of life science, Shandong University, Jinan, People’s Republic of China;2. Institute of Basic Medicine, Shandong Academy of Medical Science, Jinan, People’s Republic of China;3. State Key Laboratory of Microbial Metabolism, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai, People’s Republic of China;4. Environment Research Institute, Shandong University, Jinan, People’s Republic of China;2. Bioprocess Engineering, Wageningen University, AlgaePARC, P.O. Box 16, 6700 AA Wageningen, The Netherlands;3. Department of Life Sciences and Technology/Bioprocess Engineering, Beuth University of Applied Sciences Berlin, Seestrasse 64, 13347 Berlin Germany;1. Botany Department, Faculty of Science, Assiut University, New Valley Branch, 72511 El-Kharja, Egypt;2. Biology Department, Faculty of Science, Taibah University, 30002 Al-Madina, Saudi Arabia;3. Botany and Microbiology Department, Faculty of Science, Assiut University, 71516 Assiut, Egypt |
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| Abstract: | A typical characteristic of the butyric acid-producing Clostridium is coproduction of both butyric and acetic acids. Increasing the butyric acid selectivity important for economical butyric acid production has been rather difficult in clostridia due to their complex metabolic pathways. In this work, Clostridium acetobutylicum was metabolically engineered for highly selective butyric acid production. For this purpose, the second butyrate kinase of C. acetobutylicum encoded by the bukII gene instead of butyrate kinase I encoded by the buk gene was employed. Furthermore, metabolic pathways were engineered to further enhance the NADH-driving force. Batch fermentation of the metabolically engineered C. acetobutylicum strain HCBEKW (pta−, buk−, ctfB− and adhE1−) at pH 6.0 resulted in the production of 32.5 g/L of butyric acid with a butyric-to-acetic acid ratio (BA/AA ratio) of 31.3 g/g from 83.3 g/L of glucose. By further knocking out the hydA gene (encoding hydrogenase) in the HCBEKW strain, the butyric acid titer was not further improved in batch fermentation. However, the BA/AA ratio (28.5 g/g) obtained with the HYCBEKW strain (pta−, buk−, ctfB−, adhE1− and hydA−) was 1.6 times higher than that (18.2 g/g) obtained with the HCBEKW strain at pH 5.0, while no improvement was observed at pH 6.0. These results suggested that the buk gene knockout was essential to get a high butyric acid selectivity to acetic acid in C. acetobutylicum. |
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| Keywords: | Butyric acid Butyric acid selectivity BA/AA ratio Butyrate kinase Knockout |
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