Secretomics of Wood-Degrading Fungi and Anaerobic Rumen Fungi Associated with Biodegradation of Recalcitrant Plant Biomass

Abstract

The lignocellulose-rich plant biomass is a readily available renewable resource having immense potential to be utilized as a sustainable alternative to ever-limiting fossil fuels. It, however, resists abiotic and biotic degradation due to its complex, recalcitrant, and intricate structure comprising primarily of lignocellulose. Interestingly, few specific microbial groups have evolved unparalleled capabilities to degrade and utilize these recalcitrant biopolymers through highly coordinated and genetically evolved enzymatic processes. Of these, wood-degrading fungi and anaerobic rumen fungi are endowed with exceptional enzymatic capabilities. White rot fungi, brown rot fungi, anaerobic rumen fungi, termite gut wood-decaying fungi, and other related fungi are considered as the major natural biomass utilization systems displaying immense contributions for degradation and mineralization of recalcitrant plant biomass in an array of terrestrial habitats. Several fungal species from phyla Basidiomycota, Neocallimastigomycota, and Ascomycota mainly Phanerochaete chrysosporium, Postia placenta, Neocallimastix spp., Orpinomyces, Gloeophyllum trabeum, Trametes versicolor, Agaricus bisporus, Pleurotus ostreatus, Serpula lacrimans, and many others are capable of degrading plant cell wall constituents through secretion of hydrolytic and oxidative enzymes, collectively called carbohydrate-active enzymes (CAZymes). These enzymes are broadly classified into glycoside hydrolases (GHs), carbohydrate esterases (CEs), glycosyltransferases (GTs), polysaccharide lyases (PLs), auxiliary activities (AAs), and lytic polysaccharide monooxygenases (LPMOs). The most crucial enzymes in lignocellulose degradation are β-glucosidases, glucanases, cellobiohydrolases, xylanases, endomannanases, feruloyl esterases, laccases, lignin peroxidases, manganese peroxidases, versatile peroxidases, etc. Comparative secretome studies elucidated considerable variations in lignocellulolytic enzyme repertoire of white rot fungi, brown rot fungi, and rumen fungi. In this chapter, we discuss the fungal secretomes associated with degradation of plant matter by wood-decaying fungi and anaerobic rumen fungi. A greater insight on their remarkable enzymatic capabilities is poised to open new avenues for their future biotechnological applications in the areas of animal nutrition, biofuel, biorefinery, and bioremediation.