Post-genomic analyses of fungal lignocellulosic biomass degradation reveal the unexpected potential of the plant pathogen Ustilago maydis

Marie Couturier,Laurence Lesage-Meessen,Mireille Haon,Pedro M Coutinho,Bernard Henrissat,Didier Chevret,Caroline Olivé,Anne Favel,Jean-Guy Berrin,David Navarro

doi:10.1186/1471-2164-13-57

Abstract

BackgroundFilamentous fungi are potent biomass degraders due to their ability to thrive in ligno(hemi)cellulose-rich environments. During the last decade, fungal genome sequencing initiatives have yielded abundant information on the genes that are putatively involved in lignocellulose degradation. At present, additional experimental studies are essential to provide insights into the fungal secreted enzymatic pools involved in lignocellulose degradation.ResultsIn this study, we performed a wide analysis of 20 filamentous fungi for which genomic data are available to investigate their biomass-hydrolysis potential. A comparison of fungal genomes and secretomes using enzyme activity profiling revealed discrepancies in carbohydrate active enzymes (CAZymes) sets dedicated to plant cell wall. Investigation of the contribution made by each secretome to the saccharification of wheat straw demonstrated that most of them individually supplemented the industrial Trichoderma reesei CL847 enzymatic cocktail. Unexpectedly, the most striking effect was obtained with the phytopathogen Ustilago maydis that improved the release of total sugars by 57% and of glucose by 22%. Proteomic analyses of the best-performing secretomes indicated a specific enzymatic mechanism of U. maydis that is likely to involve oxido-reductases and hemicellulases.ConclusionThis study provides insight into the lignocellulose-degradation mechanisms by filamentous fungi and allows for the identification of a number of enzymes that are potentially useful to further improve the industrial lignocellulose bioconversion process.

Highlights

Filamentous fungi are potent biomass degraders due to their ability to thrive in ligno(hemi)celluloserich environments
Genomic analysis of the fungal carbohydrate active enzymes (CAZymes) sets dedicated to the plant cell wall To determine the sugar-cleaving capabilities of the fungi selected (Table 1), we compared their CAZyme repertoires (GH and polysaccharide lyases, PL) (Figure 1)
Clustering of the CAZyme repertoires and the selected fungi resulted in the formation of clusters of fungal species that corresponded with their fungal phyla

Summary

Introduction

Filamentous fungi are potent biomass degraders due to their ability to thrive in ligno(hemi)celluloserich environments. Additional experimental studies are essential to provide insights into the fungal secreted enzymatic pools involved in lignocellulose degradation. Filamentous fungi are among the most potent degraders of lignocellulosic biomass as they produce a high number and a broad variety of enzymes that have different and complementary catalytic activities [5]. The degradation of lignocellulose by filamentous fungi has been studied in a range of basidiomycetes and ascomycetes. The release of the T. reesei genome (QM6a strain) has shown that its carbohydrate active enzyme (CAZyme) machinery is globally comparable to other saprophytic fungi [8,9,10]. Compared to other filamentous fungi, the T. reesei genome is poor in terms of number and diversity of enzymes that are likely to be involved in biomass degradation [8]. The lack of key lignocellulosic enzymes in T. reesei opens opportunities to generate more competitive enzyme cocktails

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