S148: Engineering a microbial factory for synthesis of value-added products

One of the main research themes in my group is the development and application of new protein engineering and metabolic engineering tools for industrial biotechnology. Here I will present two specific examples.  The first example concerns the development of a new bioprocess for synthesis of xylitol, one of DOE’s top 12 platform chemicals for biorefinery.  The current processes for xylitol manufacture, based on either chemical synthesis or fermentation, all rely on the use of pure D-xylose as a feedstock, resulting in relatively high cost of production.  To address this limitation, we first used protein engineering to create a xylose reductase (XR) mutant with decreased specificity toward L-arabinose, while maintaining its high activity toward D-xylose. Then we used metabolic engineering to create an E. coli strain containing the engineered XR to efficiently produce xylitol from D-xylose with minimal production of L-arabinitol byproduct. Notably, we were able to eliminate L-arabinitol formation and produce xylitol to near 100% purity from an equiweight mixture of D-xylose, L-arabinose, and D-glucose.  The second example concerns the development of a yeast strain capable of efficiently utilizing full sugars for the economical production of biofuels.  Our efforts focus on Saccharomyces cerevisiae, the pre-eminent microorganism for industrial production of ethanol. I will report our progress on (1) construction of pentose utilization pathways in S. cerevisiae, (2) discovery and characterization pentose specific transporters; and (3) use of genome-scale modeling coupled with metabolic engineering and synthetic biology approaches to optimize sugar utilization pathways for ethanol production.