O-017. Ethanol Fermentation from Lignocellulosic Hydrolysate by a Recombinant Xylose- and Cellooligosaccharide-Assimilating Yeast Strain
Background: Lignocellulose, which is composed of cellulose, hemicellulose, and lignin, is often hydrolyzed by acid treatment; the hydrolysate obtained is then used for ethanol fermentation by microorganisms such as yeast. Because such lignocellulose hydrolysate contains not only glucose, but also various monosaccharides, such as xylose, and oligosaccharides, microorganisms should be required to efficiently ferment these sugars for the successful industrial production of ethanol. Previously, the hydrolysis of cellooligosaccharides (two to six glucose units) and an efficient ethanol production from cellobiose by a recombinant yeast strain displaying Aspergillus aculeatus β-glucosidase 1 (BGL1) on its cell surface have been achieved through cell-surface engineering in our group. Method: In this study, for the fermentations of xylose and cellobiose to ethanol, we constructed a recombinant Saccharomyces strain with xylose-fermenting ability by introducing genes of P. stipitis XR (XYL1) and XDH (XYL2), and S. cerevisiae XK (XKS1) for their intracellular expression, and with cellooligosaccharide-degrading ability by introducing the fusion gene of A. aculeatus BGL1 and 3’-half of α-agglutinin for its cell-surface display. Using this recombinant strain, we attempted ethanol fermentation from a lignocellulose hydrolysate, which was prepared by hydrolysing wood chips using concentrated sulfuric acid. Results: In the fermentation of the sulfuric acid hydrolysate of wood chips, xylose and cellooligosaccharides were completely fermented after 36 h by the recombinant strain, and then about 30 g/l ethanol was produced from 73 g/l total sugar added at the beginning. In this case, the ethanol yield of this recombinant yeast was much higher than that of the control yeast. Conclusion: These results demonstrate that the fermentation of the lignocellulose hydrolysate is performed efficiently by the recombinant Saccharomyces strain with abilities for xylose assimilation and cellooligosaccharide degradation.