Abstract
BackgroundBiomass-degrading enzymes with improved activity and stability can increase substrate saccharification and make biorefineries economically feasible. Filamentous fungi are a rich source of carbohydrate-active enzymes (CAZymes) for biomass degradation. The newly isolated LPH172 strain of the thermophilic Ascomycete Thielavia terrestris has been shown to possess high xylanase and cellulase activities and tolerate low pH and high temperatures. Here, we aimed to illuminate the lignocellulose-degrading machinery and novel carbohydrate-active enzymes in LPH172 in detail.ResultsWe sequenced and analyzed the 36.6-Mb genome and transcriptome of LPH172 during growth on glucose, cellulose, rice straw, and beechwood xylan. 10,128 predicted genes were found in total, which included 411 CAZy domains. Compared to other fungi, auxiliary activity (AA) domains were particularly enriched. A higher GC content was found in coding sequences compared to the overall genome, as well as a high GC3 content, which is hypothesized to contribute to thermophilicity. Primarily auxiliary activity (AA) family 9 lytic polysaccharide monooxygenase (LPMO) and glycoside hydrolase (GH) family 7 glucanase encoding genes were upregulated when LPH172 was cultivated on cellulosic substrates. Conventional hemicellulose encoding genes (GH10, GH11 and various CEs), as well as AA9 LPMOs, were upregulated when LPH172 was cultivated on xylan. The observed co-expression and co-upregulation of genes encoding AA9 LPMOs, other AA CAZymes, and (hemi)cellulases point to a complex and nuanced degradation strategy.ConclusionsOur analysis of the genome and transcriptome of T. terrestris LPH172 elucidates the enzyme arsenal that the fungus uses to degrade lignocellulosic substrates. The study provides the basis for future characterization of potential new enzymes for industrial biomass saccharification.
Highlights
Biomass-degrading enzymes with improved activity and stability can increase substrate saccharification and make biorefineries economically feasible
Even though the genome of T. terrestris NRRL 8126 (GenBank assembly nr GCA_000226115), sequenced in 2010, was slightly larger than that of LPH172, our analysis suggested LPH172 contained approximately 200 more genes
To identify which carbohydrate-active enzymes (CAZymes)-encoding genes were the most highly expressed on each chosen substrate, we looked at the top 20 candidates under each growth condition, ranked by their average transcripts per million (TPM) value
Summary
Biomass-degrading enzymes with improved activity and stability can increase substrate saccharification and make biorefineries economically feasible. Filamentous fungi are a rich source of carbohydrate-active enzymes (CAZymes) for biomass degradation. We aimed to illuminate the lignocellulose-degrading machinery and novel carbohydrate-active enzymes in LPH172 in detail. The biorefinery concept represents the basis for a more sustainable bio-based economy aimed at converting abundant renewable biomass sources into energy and value-added products. Even though lignocellulose is a potential biomass resource, its degradation is impeded by high lignin content and heterogeneity. Biomass saccharification into fermentable monomeric sugars by enzymatic hydrolysis is a crucial step in a biorefinery, but it is hindered by the high cost of enzymes. There is strong demand for improved enzyme activity and stability [4]
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