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Synergistic saccharification, and direct fermentation to ethanol, of amorphous cellulose by use of an engineered yeast strain codisplaying three types of cellulolytic enzyme
- Fujita, Y., Ito, J., Ueda, M., Fukuda, H., Kondo, A.
- Applied and environmental microbiology 2004 v.70 no.2 pp. 1207-1212
- Hypocrea jecorina, Saccharomyces cerevisiae, genetically modified organisms, gene expression, transgenes, endo-1,4-beta-glucanase, cellulose 1,4-beta-cellobiosidase, Aspergillus aculeatus, beta-glucosidase, enzyme activity, enzymatic hydrolysis, cellulose, saccharification, alcoholic fermentation, ethanol production
- A whole-cell biocatalyst with the ability to induce synergistic and sequential cellulose-degradation reaction was constructed through codisplay of three types of cellulolytic enzyme on the cell surface of the yeast Saccharomyces cerevisiae. When a cell surface display system based on α-agglutinin was used, Trichoderma reesei endoglucanase II and cellobiohydrolase II and Aspergillus aculeatus β-glucosidase 1 were simultaneously codisplayed as individual fusion proteins with the C-terminal-half region of α-agglutinin. Codisplay of the three enzymes on the cell surface was confirmed by observation of immunofluorescence-labeled cells with a fluorescence microscope. A yeast strain codisplaying endoglucanase II and cellobiohydrolase II showed significantly higher hydrolytic activity with amorphous cellulose (phosphoric acid-swollen cellulose) than one displaying only endoglucanase II, and its main product was cellobiose; codisplay of β-glucosidase 1, endoglucanase II, and cellobiohydrolase II enabled the yeast strain to directly produce ethanol from the amorphous cellulose (which a yeast strain codisplaying β-glucosidase 1 and endoglucanase II could not), with a yield of approximately 3 g per liter from 10 g per liter within 40 h. The yield (in grams of ethanol produced per gram of carbohydrate consumed) was 0.45 g/g, which corresponds to 88.5% of the theoretical yield. This indicates that simultaneous and synergistic saccharification and fermentation of amorphous cellulose to ethanol can be efficiently accomplished using a yeast strain codisplaying the three cellulolytic enzymes.