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Direct and efficient production of ethanol from cellulosic material with a yeast strain displaying cellulolytic enzymes

Fujita, Y., Takahashi, S., Ueda, M., Tanaka, A., Okada, H., Morikawa, Y., Kawaguchi, T., Arai, M., Fukuda, H., Kondo, A.
Applied and environmental microbiology 2002 v.68 no.10 pp. 5136-5141
Hypocrea jecorina, Saccharomyces cerevisiae, genetically modified organisms, gene transfer, Aspergillus aculeatus, beta-glucosidase, genes, gene expression, beta-glucanase, hydrolysis, enzyme activity, ethanol production, saccharification
For direct and efficient ethanol production from cellulosic materials, we constructed a novel cellulose-degrading yeast strain by genetically codisplaying two cellulolytic enzymes on the cell surface of Saccharomyces cerevisiae. By using a cell surface engineering system based on alpha-agglutinin, endoglucanase II (EGII) from the filamentous fungus Trichoderma reesei QM9414 was displayed on the cell surface as a fusion protein containing an RGSHis6 (Arg-Gly-Ser-His6) peptide tag in the N-terminal region. EGII activity was detected in the cell pellet fraction but not in the culture supernatant. Localization of the RGSHis6-EGII-alpha-agglutinin fusion protein on the cell surface was confirmed by immunofluorescence microscopy. The yeast strain displaying EGII showed significantly elevated hydrolytic activity toward barley beta-glucan, a linear polysaccharide composed of an average of 1,200 glucose residues. In a further step, EGII and beta-glucosidase 1 from Aspergillus aculeatus No. F-50 were codisplayed on the cell surface. The resulting yeast cells could grow in synthetic medium containing beta-glucan as the sole carbon source and could directly ferment 45 g of beta-glucan per liter to produce 16.5 g of ethanol per liter within about 50 h. The yield in terms of grams of ethanol produced per gram of carbohydrate utilized was 0.48 g/g, which corresponds to 93.3% of the theoretical yield. This result indicates that efficient simultaneous saccharification and fermentation of cellulose to ethanol are carried out by a recombinant yeast cells displaying cellulolytic enzymes.