title: Metabolic engineering of Escherichia coli for poly(3-hydroxybutyrate) production via threonine bypass.
abstract: BACKGROUND
  Poly(3-hydroxybutyrate) (PHB), have been considered to be good candidates for completely biodegradable polymers due to their similar mechanical properties to petroleum-derived polymers and complete biodegradability. Escherichia coli has been used to simulate the distribution of metabolic fluxes in recombinant E. coli producing poly(3-hydroxybutyrate) (PHB). Genome-scale metabolic network analysis can reveal unexpected metabolic engineering strategies to improve the production of biochemicals and biofuels.
  
  
  RESULTS
  In this study, we reported the discovery of a new pathway called threonine bypass by flux balance analysis of the genome-scale metabolic model of E. coli. This pathway, mainly containing the reactions for threonine synthesis and degradation, can potentially increase the yield of PHB and other acetyl-CoA derived products by reutilizing the CO2 released at the pyruvate dehydrogenase step. To implement the threonine bypass for PHB production in E. coli, we deregulated the threonine and serine degradation pathway and enhanced the threonine synthesis, resulting in 2.23-fold improvement of PHB titer. Then, we overexpressed glyA to enhance the conversion of glycine to serine and activated transhydrogenase to generate NADPH required in the threonine bypass.
  
  
  CONCLUSIONS
  The result strain TB17 (pBHR68) produced 6.82 g/L PHB with the yield of 0.36 g/g glucose in the shake flask fermentation and 35.92 g/L PHB with the yield of 0.23 g/g glucose in the fed-batch fermentation, which was almost 3.3-fold higher than the parent strain. The work outlined here shows that genome-scale metabolic network analysis can reveal novel metabolic engineering strategies for developing efficient microbial cell factories.
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, 300072, China. zhenquanlin@tju.edu.cn.|SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China. zhenquanlin@tju.edu.cn.|Edinburg-Tianjin Joint Research Centre for Systems Biology and Synthetic Biology, Tianjin University, Tianjin, 300072, China. zhenquanlin@tju.edu.cn.
authors.forename: Zhenquan
authors.initials: Z
authors.lastname: Lin
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, 300072, China. zhangyan12@tju.edu.cn.|SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China. zhangyan12@tju.edu.cn.|Edinburg-Tianjin Joint Research Centre for Systems Biology and Synthetic Biology, Tianjin University, Tianjin, 300072, China. zhangyan12@tju.edu.cn.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, 300072, China. yuanqian@tju.edu.cn.|SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China. yuanqian@tju.edu.cn.|Edinburg-Tianjin Joint Research Centre for Systems Biology and Synthetic Biology, Tianjin University, Tianjin, 300072, China. yuanqian@tju.edu.cn.|Key Laboratory of Systems Microbial Biotechnology, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308, China. yuanqian@tju.edu.cn.
authors.forename: Qianqian
authors.initials: Q
authors.lastname: Yuan
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, 300072, China. liuqiaojie@tju.edu.cn.|SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China. liuqiaojie@tju.edu.cn.|Edinburg-Tianjin Joint Research Centre for Systems Biology and Synthetic Biology, Tianjin University, Tianjin, 300072, China. liuqiaojie@tju.edu.cn.
authors.forename: Qiaojie
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, 300072, China. yfl@tju.edu.cn.|SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China. yfl@tju.edu.cn.|Edinburg-Tianjin Joint Research Centre for Systems Biology and Synthetic Biology, Tianjin University, Tianjin, 300072, China. yfl@tju.edu.cn.
authors.forename: Yifan
authors.initials: Y
authors.lastname: Li
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, 300072, China. zww@tju.edu.cn.|SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China. zww@tju.edu.cn.|Edinburg-Tianjin Joint Research Centre for Systems Biology and Synthetic Biology, Tianjin University, Tianjin, 300072, China. zww@tju.edu.cn.
authors.forename: Zhiwen
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Key Laboratory of Systems Microbial Biotechnology, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308, China. ma_hw@tib.cas.cn.
authors.forename: Hongwu
authors.initials: H
authors.lastname: Ma
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, 300072, China. chentao@tju.edu.cn.|SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China. chentao@tju.edu.cn.|Edinburg-Tianjin Joint Research Centre for Systems Biology and Synthetic Biology, Tianjin University, Tianjin, 300072, China. chentao@tju.edu.cn.|Department of Biochemical Engineering, School of Chemical Engineering and Technology, Tianjin University, Nankai District, 92 Weijin Road, Tianjin, 300072, China. chentao@tju.edu.cn.
authors.forename: Tao
authors.initials: T
authors.lastname: Chen
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, 300072, China. xmzhao@tju.edu.cn.|SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China. xmzhao@tju.edu.cn.|Edinburg-Tianjin Joint Research Centre for Systems Biology and Synthetic Biology, Tianjin University, Tianjin, 300072, China. xmzhao@tju.edu.cn.
authors.forename: Xueming
authors.initials: X
authors.lastname: Zhao
mesh_terms: D004926:Escherichia coli / Q000378:metabolism*; D006885:Hydroxybutyrates / Q000378:metabolism*; D060847:Metabolic Engineering / Q000379:methods*; D011091:Polyesters / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism*; D000094122:Polyhydroxybutyrates
chemical_list: D006885:Hydroxybutyrates; D011091:Polyesters; D013912:Threonine; C003182:poly-beta-hydroxybutyrate; D000094122:Polyhydroxybutyrates