Metabolic engineering of Saccharomyces cerevisiae to produce second generation ethanol from xylooligosaccharides

Abstract

Production of biofuels from lignocellulosic (LC) residues should be fuelling the energy matrix in the near future. Yeasts will play an important role as platform microorganisms for the conversion processes of LC-derived sugars into, for instance, fuel ethanol but also other advanced fuels and chemicals. Fermentation of LC hydrolysates poses many scientific and technological challenges. For example, the limitation of Saccharomyces cerevisiae in fermenting pentose sugars (derived-hemicellulose), and the pretreatment processes that generate various yeast growth inhibitors (furan-derivatives, phenolics and organic acids), reducing the efficiency of fermentation. To overcome the inability of S. cerevisiae to ferment xylose and xylodextrin (XOS), this present research proposal is linked to a thematic FAPESP project (BBSRC-FAPESP 2015/50612-8, BB/P017460/1) and aims to engineer and to improve the performance of this pathway in laboratorial (CEN.PK113-7D) and industrial (SA-1) S. cerevisiae strains engineered to efficiently transport and consume XOS. The selected strains will be engineered using a recently developed high-efficient CRISPR/Cas9 system-based approach for the industrial S. cerevisiae genome editing. For the construction of xylose consumption pathway, the xylose isomerase gene (XI) from Pyromyces sp. will be used, and xylodextrin transport and consumption genes from Neurospora crassa will be used for reconstitution of this xylodextrin utilization pathway in these strains. The transformed strains will be selected by evolutionary engineering for improved xylose and xylodextrin utilization under anaerobic conditions. The utilization of xylodextrin transporter and consumption will expand the capabilities of S. cerevisiae to utilize plant-derived and represent a potential to increase the efficiency of second generation biofuel production.