title: Cellulosic ethanol production by combination of cellulase-displaying yeast cells.
abstract: As an effort to find suitable endoglucanases to generate cellulolytic yeast strains, two fungal endoglucanases, Thermoascus aurantiacus EGI and Trichoderma reesei EGII, and two bacterial endoglucanases, Clostridium thermocellum CelA and CelD, were expressed on the yeast surface, and their surface expression levels, pH- and temperature-dependent enzyme activities, and substrate specificities were analyzed. T. aurantiacus EGI showed similar patterns of pH- and temperature-dependent activities to those of T. reesei EGII which has been widely used due to its high enzyme activity. Although EGII showed higher carboxymethyl cellulose (CMC) degradation activity than EGI, EGI showed better activity toward phosphoric acid swollen cellulose (PASC). For ethanol production from PASC, we combined three types of yeast cells, each displaying T. aurantiacus EGI, T. reesei CBHII (exoglucanase) and Aspergillus aculeatus BGLI (β-glucosidase), instead of co-expressing these enzymes in a single cell. In this system, ethanol production can be easily optimized by adjusting the combination ratio of each cell type. A mixture of cells with the optimized EGI:CBHII:BGLI ratio of 6:2:1 produced 1.3 fold more ethanol (2.1g/l) than cells composed of an equal amount of each cell type, suggesting the usefulness of this system for cellulosic ethanol production.
authors.affiliation: School of Chemical and Biological Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-744, Republic of Korea.
authors.forename: Seung-Ho
authors.initials: SH
authors.lastname: Baek
authors.forename: Sujin
authors.initials: S
authors.lastname: Kim
authors.forename: Kyusung
authors.initials: K
authors.lastname: Lee
authors.forename: Jung-Kul
authors.initials: JK
authors.lastname: Lee
authors.forename: Ji-Sook
authors.initials: JS
authors.lastname: Hahn
mesh_terms: D001230:Aspergillus / Q000201:enzymology / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D056804:Biofuels; D018533:Biomass; D001709:Biotechnology; D002480:Cellulase / Q000235:genetics / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism*; D048013:Acetivibrio thermocellus / Q000201:enzymology / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity; D013696:Temperature; D055327:Thermoascus / Q000201:enzymology / Q000235:genetics; D014242:Trichoderma / Q000201:enzymology / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D056804:Biofuels; D017931:DNA Primers; D005656:Fungal Proteins; D011994:Recombinant Proteins; D000431:Ethanol; D002482:Cellulose; C087879:endoglucanase CelD; C074775:CelA endoglucanase; D002480:Cellulase