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

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.

Investigating Aspergillus nidulans secretome during colonisation of cork cell walls

“…The -1,3-endoglucanase EngA (AN0472) plays also a major role during autolysis and its expression is tightly correlated with that of ChiB [49]. EngA was herein detected in one spot in the cork secretome, in agreement with the aforementioned studies [46][47][48].…”

“…The genome of A. nidulans contains genes putatively encoding for peroxidases [42,67]. However, none of these protein species were identified in the cork secretome, in agreement with that observed on comparable secretomes [46][47][48].…”

“…High spectral counts of ChiB peptides have been reported in A. nidulans secretomes after prolonged growth on different lignocellulosic substrates (sorghum stover [46], leaf litter [47] and maize bran [48]). Similar to our finding, ChiB high abundance in the sorghum stover secretome was related to autolysis [46].…”

“…All these enzymes have been previously identified in A. nidulans secretomes during colonisation of sorghum stover [46], leaf litter [47] and maize bran [48]. Even if not all the polysaccharide degrading enzymes identified in the previous studies (gel free proteomics)…”

“…The accumulation of a set of A. nidulans substrate-specific proteins becomes apparent when different secretomes are compared (172, 1 and 19 in sorghum stover [46], leaf litter [47] and maize bran [48], respectively). Most of the dissimilarities in the corresponding secretomes have been associated with differences in substrate composition and incubation conditions.…”