School of Agriculture, Meiji University, 1-1-1, Higashimita, Tama-ku, Kawasaki, Kanagawa, 214-8571, Japan.
Center for Sustainable Resource Science, RIKEN, 1-7-22, Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa, 230-0045, Japan.
Metab Eng. 2021 May;65:88-98. doi: 10.1016/j.ymben.2021.03.007. Epub 2021 Mar 17.
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 CO 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 CO to carboxylic acids.
琥珀酸、富马酸和苹果酸是有价值的四碳（C4）二羧酸，可用于生产塑料和食品添加剂。C4 二羧酸是由异养生物生物合成的。然而，目前的生物生产需要与食品用途竞争的有机碳源。在此，我们报告了使用代谢工程化的集胞藻 PCC 6803 从 CO 生产 C4 二羧酸。过表达编码苹果酸脱氢酶（MDH）的 citH 导致琥珀酸、富马酸和苹果酸的产量增加。citH 的过表达增加了开放蓝藻三羧酸（TCA）循环还原分支的通量。此外，通过培养基交换进行产物提取增加了 C4 二羧酸的水平；产物抑制和介质酸化是限制琥珀酸生产的因素。我们的结果表明，MDH 是激活开放蓝藻 TCA 循环还原分支的关键调节剂。该研究结果表明，蓝藻可以作为将 CO 转化为羧酸的生物催化剂。
