Genetic engineering/ metabolic engineering approaches for improved cellulase production

Abstract Abundantly available lignocellulosic biomass holds great potential as being feedstock for production of renewable fuels and green chemicals. Therefore, the cellulolytic enzymes that saccharify cellulose and hemicellulose portions of these lignocellulolytic biomass into fermentable sugars are the key factors towards its valorization. The cellulolytic enzymes are mainly composed of cellulases, such as endoglucanases, cellobiohydrolases, and β-glucosidases or cellobiase, and a variety of hemicellulases. Certain fungal species such as Trichoderma reesei, Penicillium oxalicum, Aspergillus niger, and Neurospora crassa produce large quantity of these cellulases and thus have been exploited at the industrial scale. However, each enzymatic cocktail differs in enzyme composition and enzyme ratio, and a unique enzyme composition and enzyme ratio are required for efficient biomass hydrolysis depending upon composition of lignocellulose. Therefore, genetic engineering approaches are applied in different fungal strains to increase the efficiency of the enzyme cocktail, which will be the highlights of this chapter.