Advancing cellulose utilization and engineering consolidated bioprocessing yeasts: current state and perspectives

Despite the lack of implementation of consolidated bioprocessing (CBP) at an industrial scale, this bioconversion strategy still holds significant potential as an economically viable solution for converting lignocellulosic biomass (LCB) into biofuels and green chemicals, provided an appropriate organism can be isolated or engineered. The use of Saccharomyces cerevisiae for this purpose requires, among other things, the development of a cellulase expression system within the yeast. Over the past three decades, numerous studies have reported the expression of cellulase-encoding genes, both individually and in combination, in S. cerevisiae. Various strategies have emerged to produce a core set of cellulases, with differing degrees of success. While one-step conversion of cellulosic substrates to ethanol has been reported, the resulting titers and productivities fall well below industrial requirements. In this review, we examine the strategies employed for cellulase expression in yeast, highlighting the successes in developing basic cellulolytic CBP-enabled yeasts. We also summarize recent advancements in rational strain design and engineering, exploring how these approaches can be further enhanced through modern synthetic biology tools to optimize CBP-enabled yeast strains for potential industrial applications. KEY POINTS: • S. cerevisiae's lack of cellulolytic ability warrants its engineering for industry. • Advancements in the expression of core sets of cellulases have been reported. • Rational engineering is needed to enhance cellulase secretion and strain robustness. • Insights gained from omics strategies will direct the future development of CBP strains.