Abstract
BackgroundThe recombinant yeast strains displaying the heterologous cellulolytic enzymes on the cell surface using the glycosylphosphatidylinositol (GPI) anchoring system are considered promising biocatalysts for direct conversion of lignocellulosic materials to ethanol. However, the cellulolytic activities of the conventional cellulase-displaying yeast strains are insufficient for the hydrolysis of cellulose. In this study, we constructed novel gene cassettes for the efficient cellulose utilization by cellulase-displaying yeast strains.ResultsThe novel gene cassettes for the cell-surface display of Aspergillus aculeatus β-glucosidase (BGL1) and Trichoderma reeseii endoglucanase II (EGII) were constructed using the promoter and the GPI anchoring region derived from Saccharomyces cerevisiae SED1. The gene cassettes were integrated into the S. cerevisiae genome, then the β-glucosidase activity of these recombinant strains was evaluated. We revealed that simultaneous utilization of the SED1 promoter and Sed1 anchoring domain in a gene cassette enabled highly-efficient enzyme integration into the cell wall. The β-glucosidase activity of recombinant yeast cells transduced with the novel gene cassette was 8.4-fold higher than that of a conventional strain. The novel EGII-displaying strain also achieved 106-fold higher hydrolysis activity against the water-insoluble cellulose than a conventional strain. Furthermore, direct ethanol production from hydrothermally processed rice straw was improved by the display of T. reeseii EGII using the novel gene cassette.ConclusionsWe have developed novel gene cassettes for the efficient cell-surface display of exo- and endo-type cellulolytic enzymes. The results suggest that this gene cassette has the wide applicability for cell-surface display and that cellulase-displaying yeasts have significant potential for cost-effective bioethanol production from lignocellulosic biomass.
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