Tuesday, May 1, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
While fermenting mixed sugars (glucose, xylose, and galactose) in hydrolyzates from terrestrial or marine biomass, naturally existing or engineered microorganisms preferentially ferment glucose over non-glucose sugars. This sequential utilization often results in lower overall yield and productivity of biofuels. To overcome these bottlenecks, we engineered yeasts to co-ferment mixtures of cellobiose and xylose. After constructing an efficient xylose-fermenting strain of Saccharomyces cerevisiae through rational and combinatorial strategies, we introduced a cellobiose utilizing pathway into the xylose-fermenting strain. In this yeast strain, hydrolysis of cellobiose takes place inside yeast cells through the action of an intracellular β-glucosidase following import by a cellodextrin transporter (1). The resulting yeast strain not only co-fermented cellobiose and xylose simultaneously, but also exhibited improved ethanol yield as compared when either cellobiose or xylose was used as a sole carbon source (2). With a similar strategy, we demonstrate that co-fermentation of cellobiose and galactose (3) and enhanced production of xylitol from a mixture of cellobiose and xylose (4) are also feasible. Our results suggest that this simultaneous co-fermentation of mixed sugars is a promising strategy for producing fuels and chemicals from plant biomass.
- Galazka et al. Science 330:84-86 (2010)
- Ha et al. Proc. Natl. Acad. Sci. USA 108:504-509 (2011)
- Ha et al. Appl. Environ. Microbiol. 77: 5822-5826 (2011)
- Oh et al. AIChE Annual Meeting (2011)