Podospora anserina Hemicellulases Potentiate the Trichoderma reesei Secretome for Saccharification of Lignocellulosic Biomass

Abstract

To improve the enzymatic hydrolysis (saccharification) of lignocellulosic biomass by Trichoderma reesei , a set of genes encoding putative polysaccharide-degrading enzymes were selected from the coprophilic fungus Podospora anserina using comparative genomics. Five hemicellulase-encoding genes were successfully cloned and expressed as secreted functional proteins in the yeast Pichia pastoris . These novel fungal CAZymes belonging to different glycoside hydrolase families ( Pa Man5A and Pa Man26A mannanases, Pa Xyn11A xylanase, and Pa Abf51A and Pa Abf62A arabinofuranosidases) were able to break down their predicted cognate substrates. Although Pa Man5A and Pa Man26A displayed similar specificities toward a range of mannan substrates, they differed in their end products, suggesting differences in substrate binding. The N-terminal CBM35 module of Pa Man26A displayed dual binding specificity toward xylan and mannan. Pa Xyn11A harboring a C-terminal CBM1 module efficiently degraded wheat arabinoxylan, releasing mainly xylobiose as end product. Pa Abf51A and Pa Abf62A arabinose-debranching enzymes exhibited differences in activity toward arabinose-containing substrates. Further investigation of the contribution made by each P. anserina auxiliary enzyme to the saccharification of wheat straw and spruce demonstrated that the endo-acting hemicellulases ( Pa Xyn11A, Pa Man5A, and Pa Man26A) individually supplemented the secretome of the industrial T. reesei CL847 strain. The most striking effect was obtained with Pa Man5A that improved the release of total sugars by 28% and of glucose by 18%, using spruce as lignocellulosic substrate.