Coupling the pretreatment and hydrolysis of lignocellulosic biomass by the expression of beta‐xylosidases

Thermochemical pretreatment and enzymatic hydrolysis are the areas contributing most to the operational costs of second generation ethanol in lignocellulosic biorefineries. The improvement of lignocellulosic enzyme cocktails has been significant in the recent years. Although the needs for the reduction of the energy intensity and chemical consumption in the pretreatment step are well known, the reduction of the severity of the process strongly affects the enzymatic hydrolysis yield. To explore the formulation requirements of the well known cellulolytic cocktail from Myceliophthora thermophila on mild pretreated raw materials, this cocktail was tested on steam exploded corn stover without acid impregnation. The low hemicellulose yield and significant accumulation of xylobiose compared with the standard pretreated material obtained with dilute acid impregnation evidenced a clear limitation in the conversion of xylan to xylose. In order to complement the beta‐xylosidase limitation, a selection of enzymes was expressed and tested in this fungus. A controlled expression of xylosidases from Aspergillus nidulans, Aspergillus fumigatus, and Fusarium oxysporum allowed recovering hemicellulose yields reached with standard acid treated material. The results underline the need of parallel development of the pretreatment process with the optimization of the formulation of the enzymatic cocktails. Cellulolytic cocktail from Myceliophthora thermophila was tested on mild pretreated raw materials. A low xylose yield and a significant accumulation of xylobiose were observed, compared with the currently pretreated material (including dilute acid impregnation) evidencing a limitation in the xylan conversion. To increase the beta‐xylosidase activity, a selection of enzymes was tested in this fungus. The results evidence the importance of encompassing the improvement of the enzymatic cocktails with the development of the pretreatment step for the next generation biorefineries.