Production of 2,3-butanediol from cellulosic biomass by engineered Saccharomyces cerevisiae deficient in Pdc

A 2,3-butanediol (2,3-BD) can be produced from glucose either using wild-type or engineered microorganisms. The utilization of xylose that abundant in lignocellulosic hydrolyzate would make the production of 2,3-BD more sustainable and economical. Saccharomyces cerevisiae for instance, can produce only little amounts of 2,3-BD from glucose, but not able to ferment xylose to other by-products. Therefore, it is necessary to introduce both 2,3-BD production and xylose assimilation pathways into S. cerevisiae for producing 2,3-BD from xylose. As ethanol is a major fermentation product by S. cerevisiae, a pyruvate decarboxylase (Pdc)-deficient mutant (SOS4) was used as a host in order to increase carbon flux toward 2,3-BD instead of ethanol. The XYL1, XYL2, and XYL3 genes coding for xylose assimilating enzymes derived from Scheffersomyces stipitis were introduced into the SOS4 strain to enable xylose utilization. The resulting strain (SOS4X) that accumulate pyruvate which is a intermediate for 2,3-BD, from xylose without ethanol production. Additionally, the alsS and alsD genes from Bacillus subtilis and endogenous BDH1 gene were overexpressed in the SOS4X to increase 2,3-BD production from xylose. As a result, the resulting strain (BD4X) produced 20.7 g/L of 2,3-BD from xylose with a yield of 0.27 g 2,3-BD/g xylose. The titer of 2,3-BD from xylose increased up to 43.6 g/L under a fed-batch fermentation. The BD4X strain produced (R, R)-2,3-BD dominantly (>97 % of the total 2,3-BD) with trace amounts of meso-2,3-BD. These results suggest that S. cerevisiae might be a promising host for producing 2,3-BD from lignocellulosic biomass for industrial applications.