Tuesday, April 30, 2013
Exhibit Hall
The high value compound 1,2,4-butanetriol (BT) is a direct precursor for synthesis of an energetic material 1,2,4-butanetriol trinitrate, a nitroglycerin homolog. The biosynthesis of BT directly from D-xylose, the most abundant pentose sugar in woody biomass, consists of four enzymatic steps: D-xylose → D-xylonic acid → 2-keto-3-deoxy-D-xylonate → 3,4-dihydroxybutanal → BT. The second and last enzymes are endogenous to the strain used while the other two key enzymes were recruited: xylose dehydrogenase (xdh from Caulobacter crescentus) catalyzing the conversion of D-xylose to D-xylonic acid and a 2-ketoacid decarboxylase (mdlC from Pseudomonas putida) catalyzing the conversion of 2-keto-3-deoxy-D-xylonate to 3,4-dihydroxybutanal. These two exogenous genes were overexpressed in a xylose metabolism-deficient Escherichia coli W3110 ΔxylAB. The xylose dehydrogenase was previously characterized in earlier works while a codon optimized mdlC was used in this study. The mdlC led to 20% increase in protein expression and a 2.8 fold increase of BT titer from the prototype strain. This was further improved by changing the control of induction from an IPTG-inducible promoter to a constitutive promoter, blocking a competing reaction that converts 2-keto-3-deoxy-D-xylonate to pyruvate and glycoaldehyde (ΔyjhHΔyagE) and using a single plasmid system. Further work is done to increase the titer of BT by overexpression of the endogenous enzymes catalyzing the second and last step coded by yjhG and adhP respectively.
This work was supported by Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012-0006693).