Expression of catalytically efficient xylanases from thermophilic fungus Malbranchea cinnamomea for synergistically enhancing hydrolysis of lignocellulosics

In this study, two xylanase genes (GH10 and GH11) derived from Malbranchea cinnamomea, designated as XYN10A_MALCI and XYN11A_MALCI, respectively, were expressed in Pichia pastoris X33. The maximum level of xylanase expression was found to be 24.3 U/ml for rXYN10A_MALCI and 573.32 U/ml for rXYN11A_MALCI. The purified recombinant rXYN11A_MALCI was stable at 70° C and catalytically active against a variety of substituted (arabinoxylans) as well as unsubstituted xylans. The hydrolytic potential of recombinant xylanases for enhancing the hydrolysis of acid/alkali pretreated lignocellulosics (rice straw and bagasse) by the commercial cellulase Cellic CTec2 was assessed which revealed that both rXYN10A_MALCI and rXYN11A_MALCI act synergistically with commercial cellulases and resulted in 1.54 and 1.58 folds improved hydrolysis of acid treated rice straw and alkali treated rice straw using cocktail comprising of Cellic CTec2 and XYN11A_MALCI (8:2 ratio) when compared to Cellic CTec2 alone at same protein loading rate of (∼5.7 mg/g biomass).