Triggering the Expression of Cellulolytic Genes Using a Recombinant Endoxylanase from Trichoderma harzianum IOC-3844

Abstract

Xylanases are used in several biotechnological processes, primarily for biopulping and biobleaching in the paper industry and as accessory enzymes for bioethanol production. In this study, a recombinant family 10 endoxylanase from Trichoderma harzianum strain IOC-3844 was expressed and characterized biochemically. Concomitantly, the effects of different culture conditions on the regulation of xylanases and cellulolytic genes in T. harzianum were investigated. The recombinant protein was expressed in two major forms by Pichia pastoris: one form with a molecular mass of 35 kDa (non-glycosylated) and another form with a molecular mass of 60 kDa (glycosylated). Both forms showed optimal xylanolytic activity at 40 °C and pH 6.5. Glycosylation resulted in a twofold higher catalytic efficiency for the recombinant enzyme. In transcriptional studies, in contrast to the findings reported for Trichoderma reesei xyn3, the xyn3 gene from T. harzianum IOC-3844 was up-regulated in the presence of xylan. Moreover, stronger and faster expression of the analyzed genes (xyn2, xyn3, and egl3) was observed during cultivation with cellulose and xylan together. We employed the recombinant xyn3 during the cultivation of T. harzianum in steam-exploded bagasse to release the remaining xylan bound to the cellulose. Interestingly, the addition of Xyn3 accelerated the expression of xylanases and other genes of the cellulolytic system (egl1, egl3, cbh2, and swo1). Our results provide a potential strategy for triggering the expression of xylanases and cellulases in T. harzianum IOC-3844. The addition of Xyn3 can improve the expression of lignocellulolytic genes considerably when the fungus is cultivated with sugarcane bagasse.