Combined Cell Surface Display of β-d-Glucosidase (BGL), Maltose Transporter (MAL11), and Overexpression of Cytosolic Xylose Reductase (XR) in Saccharomyces cerevisiae Enhance Cellobiose/Xylose Coutilization for Xylitol Bioproduction from Lignocellulosic Biomass.

Xylitol is a highly valuable commodity chemical used extensively in the food and pharmaceutical industries. The production of xylitol from d-xylose involves a costly and polluting catalytic hydrogenation process. Biotechnological production from lignocellulosic biomass by micro-organisms like yeasts is a promising option. In this study, xylitol is produced from lignocellulosic biomass by a recombinant strain of Saccharomyces cerevisiae (S. cerevisiae) (YPH499-SsXR-AaBGL) expressing cytosolic xylose reductase (Scheffersomyces stipitis xylose reductase [SsXR]), along with a β-d-glucosidase (Aspergillus aculeatus β-glucosidase 1 [AaBGL]) displayed on the cell surface. The simultaneous cofermentation of cellobiose/xylose by this strain leads to an ≈2.5-fold increase in Yxylitol/xylose (=0.54) compared to the use of a glucose/xylose mixture as a substrate. Further improvement in the xylose uptake by the cell is achieved by a broad evaluation of several homologous and heterologous transporters. Homologous maltose transporter (ScMAL11) shows the best performance in xylose transport and is used to generate the strain YPH499-XR-ScMAL11-BGL with a significantly improved xylitol production capacity from cellobiose/xylose coutilization. This report constitutes a promising proof of concept to further scale up the biorefinery industrial production of xylitol from lignocellulose by combining cell surface and metabolic engineering in S. cerevisiae.