Cell surface engineering of Saccharomyces cerevisiae for simultaneous valorization of corn cob and cheese whey via ethanol production

The viability of 2nd generation bioethanol processes is dependent on achieving high ethanol titers, which requires the use of high solid loadings that will negatively affect the fermentative microorganism besides increasing enzyme-associated costs. To solve this, and also problems of feedstock availability, lignocellulosic biomass can be mixed with dairy by-products to increase carbon content. In this study, industrial strains of Saccharomyces cerevisiae, with improved thermotolerance and stress resistance, were engineered for the cell surface display of cellulolytic enzymes and were evaluated in consolidated bioprocessing of cellulose. Additionally, -galactosidase was also displayed to enable lactose consumption, resulting in high ethanol titers (>50 g/L) from the simultaneous use of cheese whey and pretreated corn cob as substrate. The multi-feedstock valorization approach together with this lactose-consuming cellulolytic yeast allowed the reduction on materials costs by 60% with a 2.5-fold increase in the annual ethanol production, therefore contributing to the establishment of economic viable ethanol processes.This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UIDB/04469/2020, the MIT-Portugal Program (Ph.D. Grant PD/BD/128247/2016 to Joana T. Cunha), and Biomass and Bioenergy Research Infrastructure (BBRI)-LISBOA-01-0145-FEDER-022059, supported by Operational Programme for Competitiveness and Internationalization (PORTUGAL2020), by Lisbon Portugal Regional Operational Programme (Lisboa 2020) and by North Portugal Regional Operational Programme (Norte 2020) under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). The authors acknowledge Professor Emile van Zyl and Stellenbosch University for providing the sequences encoding cellobiohydrolase 1 from Talaromyces emersonii (CBH1) and cellobiohydrolase 2 from Chrysosporium lucknowense (CBH2).