Influence of Key Factors on Hydrolytic Enzyme Production by High Performance Recombinant Yeast for Consolidated Bioprocessing

Consolidated Bioprocessing (CBP) is a promising technology for integrated biorefineries in which enzyme production, biomass hydrolysis, and the fermentation of C5 and C6 sugars into second-generation ethanol (2G ethanol) or other bioproducts are integrated into a single bioreactor. However, the development of a highly suitable microorganism for CBP, that efficiently secretes enzymes and ferments all released sugars simultaneously is still a challenge. Additionally, the selection of process conditions to enhance enzyme production and consequently biomass conversion is of high importance. In the present study, the influence of key process conditions on the production of hydrolytic enzymes and 2G ethanol by the yeast Saccharomyces cerevisiae AC14 (producer of seven hydrolytic enzymes) was investigated, aiming for its application in CBP. When evaluating the composition of the fermentative medium, pH and oxygen supply, the best results in enzymatic activities per dry cell weight - dcw (2.13 IU.g −1 dcw of total cellulases, 102.0 U.g −1 dcw of xylanases, 7.38 U.g − 1 dcw of β-glucosidase and 25.5 U.g −1 dcw of β-xylosidase), ethanol yield (90.3%) and ethanol productivity (1.0 g.L − 1 .h − 1 ) were obtained using a fermentative medium containing a mixture of monomers and polymers, pH of 5.5 and anaerobic conditions. Most importantly, the presence of xylan was found to be crucial for cellulase secretion. Under the most appropriate conditions, repeated batches were carried out with cell recycling, reaching 10 cycles with total substrate conversion. Thus, the new knowledge regarding CBP obtained contributes to enhance its potential application in an integrated biorefinery context.