Tuesday, April 30, 2013
Exhibit Hall
Saccharomyces cerevisiae can be engineered to ferment cellodextrin, intermediate oligosaccharides of the cellulose hydrolysis by cellulase. Direct fermentation of cellodextrin rather than glucose can be advantageous because glucose not only inhibits cellulose activity, but also cause glucose repression hampering utilization of non-glucose sugars present in cellulosic hydrolyzates. In order to facilitate cellodextrin utilization by S. cerevisiae, a fungal cellodextrin utilizing pathway from Neurospora crassa consisting of a cellodextrin transporter and a cellodextrin hydrolase were introduced into S. cerevisiae. Two types of cellodextrin transporters (cdt-1 and cdt-2) have been identified from N. crassa previously but their kinetic properties and efficiency for cellobiose fermentation in S. cerevisiae have not been studied yet. In this study, the cellobiose transporters (cdt-1 and cdt-2), which are hypothesized to transport cellodextrin with distinct mechanisms, were introduced into S. cerevisiae along with intracellular β-glucosidase (gh1-1). Cellobiose transporter assays of the resulting strains suggested that CDT-1 is a symporter while CDT-2 is a facilitator. When the engineered strains were investigated for their cellobiose fermentation efficiency under various conditions, the strain (DCDT-1G) expressing cdt-1 and gh1-1 showed faster cellobiose fermentation than the strain (DCDT-2G) expressing cdt-2 and gh1-1 under various culture conditions with different medium and aeration. While CDT-2 has potential energetic benefits, the expression levels and kinetic properties of CDT-2 in S. cerevisiae might not be optimum for cellobiose fermentation. These results suggest CDT-1 is a more effective cellobiose transporter than CDT-2 for engineering S. cerevisiae to ferment cellobiose.