(15e) Establishing a Platform Escherichia coli Strain to Generate Xylose-Derived Value-Added Products
Xylose is the most abundant C5 sugar in lignocellulosic biomass and also represents a source of carbon from non-edible feedstocks. Here, we report the construction of a platform Escherichia coli strain for the production of high value compounds via the nonphosphorylative xylose metabolism. Firstly, a 3,4-dihydroxybutanal over-producing pathway was constructed by efficient enzymes screening and host strain engineering. Then two 3,4-dihydroxybutanal dehydrogenases were identified to efficiently convert 3,4-dihydroxybutanal into 3,4-dihydroxybutyric acid (3,4-DHBA), which is the hydrolyzed form of 3-Hydroxy-Î³-butyrolactone (3HBL). 3HBL is one of the top value-added building block for synthesis of various drugs and nutraceuticals. This novel 3,4-DHBA biosynthetic pathway produced 1.27 g/L of 3,4-DHBA in shake flasks, which is the highest titer reported so far. The application of this platform was further demonstrated by building an artificial pathway for biosynthesis of 1,4-butanediol (1,4-BDO). The 3,4-dihydroxybutanal over-producing strain was transformed into a 1,2,4-butanetriol (1,2,4-BTO) over-producing strain by over-expression of endogenous alcohol dehydrogenase, which enabled 1.5 g/L 1,2,4-BTO produced from xylose. Then the Klebsiella oxytoca diol dehydratase was engineered to achieve non-native catalysis of 1,2,4-BTO into 1,4-BDO by a series of rational protein engineering strategies. Those efforts enabled 209 mg/L 1,4-BDO produced via a novel metabolic route from xylose. This work demonstrates great potential for large-scale production of 3,4-DHBA and sets an example to build novel biosynthetic pathways via rational protein engineering.