| Institution: | 1. State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, Nanjing 211800, PR China;2. Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University, Nanjing 211800, PR China;1. Biosciences Center, National Renewable Energy Laboratory, Golden, CO, USA;2. Institute of Plant Biology, National Taiwan University, Taipei, Taiwan;3. Institute of Pharmacology, Kaohsiung Medical University, Kaohsiung, Taiwan;4. Department of Genome Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan;1. Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan;2. Graduate School of Science, Technology and Innovation, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan;3. Biological Resources and Post-Harvest Division, Japan International Research Center for Agricultural Sciences (JIRCAS), 1-1 Ohwashi, Tsukuba, Ibaraki 305-8686, Japan;1. Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN 37235, USA;2. Department of Biological Sciences, Vanderbilt University, Nashville, TN 27235, USA;3. Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 27235, USA |
| Abstract: | Succinate, fumarate, and malate are valuable four-carbon (C4) dicarboxylic acids used for producing plastics and food additives. C4 dicarboxylic acid is biologically produced by heterotrophic organisms. However, current biological production requires organic carbon sources that compete with food uses. Herein, we report C4 dicarboxylic acid production from CO2 using metabolically engineered Synechocystis sp. PCC 6803. Overexpression of citH, encoding malate dehydrogenase (MDH), resulted in the enhanced production of succinate, fumarate, and malate. citH overexpression increased the reductive branch of the open cyanobacterial tricarboxylic acid (TCA) cycle flux. Furthermore, product stripping by medium exchanges increased the C4 dicarboxylic acid levels; product inhibition and acidification of the media were the limiting factors for succinate production. Our results demonstrate that MDH is a key regulator that activates the reductive branch of the open cyanobacterial TCA cycle. The study findings suggest that cyanobacteria can act as a biocatalyst for converting CO2 to carboxylic acids. |
