Synergistic effect and application of xylanases as accessory enzymes to enhance the hydrolysis of pretreated bagasse

Abstract

Recently, the new trend in the second-generation ethanol industry is to use mild pretreatments, in order to reduce costs and to keep higher content of hemicellulose in the biomass. Nevertheless, a high enzyme dosage is still required in the conversion of (hemi)cellulose. The interaction between cellulases and xylanases seems to be an effective alternative to reduce enzyme loading in the saccharification process. At first, to evaluate the synergism of xylanases on bagasse degradation, we have produced two xylanases from glycoside hydrolase family 10 (GH10) and three xylanases from glycoside hydrolase family 11 (GH11), from two thermophilic organisms, Thermobifida fusca and Clostridium thermocellum, and one mesophilic organism, Streptomyces lividans. Peracetic acid (PAA) pretreated bagasse was used as substrate. The combination of XynZ-C (GH10, from C. thermocellum), and XlnB (GH11, from S. lividans) presented the highest degree of synergy after 6. h (3.62). However, the combination of XynZ-C and Xyn11A (GH11, from T. fusca) resulted in the highest total yield of reducing sugars. To evaluate the synergism between xylanases and cellulases, commercial cellulase preparation from Trichoderma reesei was combined with the selected xylanases, XynZ-C and Xyn11A. About 2-fold increase was observed in the concentration of reducing sugars, when both xylanases, XynZ-C and Xyn11A, were added together with T. reesei cellulases in the reaction mixture.