Development of Cellulase-Producing Industrial Saccharomyces cerevisiae Strains for Consolidated Bioprocessing

Over the last 25 years the concept of converting abundant lignocellulosic biomass resources to renewable commodity products through microbial conversion has been widely explored. Despite the promise of renewable, sustainable fuels and chemicals from feedstocks that limit interference with food production, cellulosic ethanol production at industrial scale is limited. Reasons for this include the recalcitrance, variability, and low energy density of the feedstock, as well as the significant capital and operations costs involved. Other process-related issues such as the invariably stressful fermentation conditions in cellulosic ethanol production have also been identified and strategies to mitigate these problems have been researched. Consolidated bioprocessing (CBP) with the industrial ethanologenic yeast Saccharomyces cerevisiae could address several of these complications if process-ready strains can be developed. This chapter will discuss the status quo of developing S. cerevisiae strains for CBP of cellulosic substrates. It will highlight expression of cellulases and strategies to improve this heterologous expression, including advances in rational engineering interventions and improved strain backgrounds. The possibility of improving strain robustness through knowledge gained from omics studies is also explored. Subsequently, we will shift focus to the possibility of producing other commodity chemicals using these yeasts, highlighting various metabolic engineering efforts to establish a greater product range from lignocellulose-derived sugars for a biorefinery concept.