Sunday, April 29, 2007

Development of cellulose and xylose utilizing Saccharomyces cerevisiae strains for consolidated bioprocessing

A. Kondo, Biochemical Engineering Laboratory (CX-12), Faculty of Engineering, Department of Chemical Science and Engineering, Kobe University, 1-1 Rokkodaicho, Nada-ku, Kobe, 657-8501, Japan and H. Fukuda, Biochemical Engineering Laboratory (CX-12), Graduate School of Science and Technology, Department of Molecular Science and Material Engineering, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, 657-8501, Japan.

For direct and efficient ethanol production from cellulosic materials, we constructed a novel cellulose-degrading yeast strain by genetically co-displaying three types of cellulolytic enzymes on the cell surface of Saccharomyces cerevisiae. Trichoderma reesei endoglucanase II (EGII), cellobiohydrolase II (CBHII) and Aspergillus aculeatus b-glucosidase 1 (BGL1) were simultaneously co-displayed as fusion proteins with the C-terminal half region of a-agglutinin. A yeast strain co-displaying EG II and CBHII showed significantly higher hydrolytic activity toward amorphous cellulose (phosphoric acid-swollen cellulose) than one displaying only EGII, and the synergism between EGII and CBHII was successfully induced on the yeast-cell surface. Co-display of BGL1, EGII, and CBHII enabled the yeast strain to directly produce ethanol from amorphous cellulose. This result indicates that efficient and simultaneous saccharification and fermentation of cellulose to ethanol is carried out by a recombinant yeast cells displaying cellulolytic enzymes. We also constructed the recombinant strain that was able to ferment xylose and cellulosic materials by displaying cellulolytic enzymes on the cell surface of xylose utilizing strains constructed by expressing xylose reductase (XR), xylitol dehydrogenase (XDH) and xylulokinase (XK). The fermentation of lignocellulose hydrolysate has shown to be performed efficiently by the recombinant Saccharomyces strain endued properties of xylose assimilation and cellulose degradation.
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(3)   Katahira S. et al., Appl. Microbiol. Biotechnol., 72, 1136-1143 (2006).

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