Zhongxi Zhang1,2,3, Yang Yang1,2,3, Yike Wang1,2,3, Jinjie Gu2,3, Xiyang Lu2, Xianyan Liao1, Jiping Shi2,4, Chul Ho Kim5, Gary Lye6, Frank Baganz7, Jian Hao8,9. 1. School of Life Science, Shanghai University, Shanghai, 200444, People's Republic of China. 2. Lab of Biorefinery, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai, 201210, People's Republic of China. 3. University of Chinese Academy of Sciences, Beijing, 100049, People's Republic of China. 4. School of Life Science and Technology, ShanghaiTech University, Shanghai, People's Republic of China. 5. Microbial Biotechnology Research Center, Jeonbuk Branch Institute, KRIBB, Jeongeup, Jeonbuk, 556212, South Korea. 6. Department of Biochemical Engineering, University College London, Gordon Street, London, WC1H 0AH, UK. 7. Department of Biochemical Engineering, University College London, Gordon Street, London, WC1H 0AH, UK. f.baganz@ucl.ac.uk. 8. Lab of Biorefinery, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai, 201210, People's Republic of China. haoj@sari.ac.cn. 9. Department of Biochemical Engineering, University College London, Gordon Street, London, WC1H 0AH, UK. haoj@sari.ac.cn.
Abstract
BACKGROUND: Biological routes for ethylene glycol production have been developed in recent years by constructing the synthesis pathways in different microorganisms. However, no microorganisms have been reported yet to produce ethylene glycol naturally. RESULTS: Xylonic acid utilizing microorganisms were screened from natural environments, and an Enterobacter cloacae strain was isolated. The major metabolites of this strain were ethylene glycol and glycolic acid. However, the metabolites were switched to 2,3-butanediol, acetoin or acetic acid when this strain was cultured with other carbon sources. The metabolic pathway of ethylene glycol synthesis from xylonic acid in this bacterium was identified. Xylonic acid was converted to 2-dehydro-3-deoxy-D-pentonate catalyzed by D-xylonic acid dehydratase. 2-Dehydro-3-deoxy-D-pentonate was converted to form pyruvate and glycolaldehyde, and this reaction was catalyzed by an aldolase. D-Xylonic acid dehydratase and 2-dehydro-3-deoxy-D-pentonate aldolase were encoded by yjhG and yjhH, respectively. The two genes are part of the same operon and are located adjacent on the chromosome. Besides yjhG and yjhH, this operon contains four other genes. However, individually inactivation of these four genes had no effect on either ethylene glycol or glycolic acid production; both formed from glycolaldehyde. YqhD exhibits ethylene glycol dehydrogenase activity in vitro. However, a low level of ethylene glycol was still synthesized by E. cloacae ΔyqhD. Fermentation parameters for ethylene glycol and glycolic acid production by the E. cloacae strain were optimized, and aerobic cultivation at neutral pH were found to be optimal. In fed batch culture, 34 g/L of ethylene glycol and 13 g/L of glycolic acid were produced in 46 h, with a total conversion ratio of 0.99 mol/mol xylonic acid. CONCLUSIONS: A novel route of xylose biorefinery via xylonic acid as an intermediate has been established.
BACKGROUND: Biological routes for ethylene glycol production have been developed in recent years by constructing the synthesis pathways in different microorganisms. However, no microorganisms have been reported yet to produce ethylene glycol naturally. RESULTS: Xylonic acid utilizing microorganisms were screened from natural environments, and an Enterobacter cloacae strain was isolated. The major metabolites of this strain were ethylene glycol and glycolic acid. However, the metabolites were switched to 2,3-butanediol, acetoin or acetic acid when this strain was cultured with other carbon sources. The metabolic pathway of ethylene glycol synthesis from xylonic acid in this bacterium was identified. Xylonic acid was converted to 2-dehydro-3-deoxy-D-pentonate catalyzed by D-xylonic acid dehydratase. 2-Dehydro-3-deoxy-D-pentonate was converted to form pyruvate and glycolaldehyde, and this reaction was catalyzed by an aldolase. D-Xylonic acid dehydratase and 2-dehydro-3-deoxy-D-pentonate aldolase were encoded by yjhG and yjhH, respectively. The two genes are part of the same operon and are located adjacent on the chromosome. Besides yjhG and yjhH, this operon contains four other genes. However, individually inactivation of these four genes had no effect on either ethylene glycol or glycolic acid production; both formed from glycolaldehyde. YqhD exhibits ethylene glycol dehydrogenase activity in vitro. However, a low level of ethylene glycol was still synthesized by E. cloacae ΔyqhD. Fermentation parameters for ethylene glycol and glycolic acid production by the E. cloacae strain were optimized, and aerobic cultivation at neutral pH were found to be optimal. In fed batch culture, 34 g/L of ethylene glycol and 13 g/L of glycolic acid were produced in 46 h, with a total conversion ratio of 0.99 mol/mol xylonic acid. CONCLUSIONS: A novel route of xylose biorefinery via xylonic acid as an intermediate has been established.
Authors: Barbara Bourgade; Christopher M Humphreys; James Millard; Nigel P Minton; M Ahsanul Islam Journal: ACS Synth Biol Date: 2022-05-11 Impact factor: 5.249