Unraveling the secretome of Termitomyces clypeatus grown on agroresidues as a potential source for bioethanol production

Abstract

Termitomyces clypeatus MTCC 5091 is an edible mushroom and is prized for its nutritional value as well as for harboring plethora of enzymes essential for carbohydrate degradation. T. clypeatus when grown on agricultural based carbon sources efficiently induced high quantities of lignocellulolytic enzymes in the secretome. Optimization in tamarind kernal powder (TKP) media through response surface methodology enhanced the enzyme yields by several folds. Correlation between extracellular protein productions of the fungus with respect to its specific growth rate established that secreted proteins were produced most efficiently at low specific growth rates. Proteins released in the T. clypeatus secretome were quantified and identified using SDS-PAGE, 2D gel electrophoreses, zymography and matrix-assisted laser desorption mass spectrometry. 36 proteins identified from the protein spots belonged majority to glucosyl hydrolase family, transporters, uncharacterized and hypothetical proteins. The potential synergistic interactions between the cellulases and xylanases in enzyme preparations of T. clypeatus during hydrolysis of steam pretreated bagasse (SPB) showed improved hydrolysis efficiency and enhanced rate of hydrolysis as observed in high performance liquid chromatograpy. The changes in the ultra-structure of SPB after 12h enzymatic hydrolysis were observed by scanning electron microscopy. The hydrolysates obtained produced ∼7.2g/L ethanol after 6h fermentation determined by gas chromatography.