Myceliophthora thermophila Xyr1 is predominantly involved in xylan degradation and xylose catabolism

Ana Carolina Dos Santos Gomes,Ronald P De Vries,Mao Peng,Nancy Coconi Linares,Maira Nicolau De Almeida,Jean-Paul Meijnen,Evy Battaglia,Daniel Falkoski,Jaap Visser

doi:10.1186/s13068-019-1556-y

Ana Carolina Dos Santos Gomes, Ronald P De Vries + Show 7 more

Open Access

https://doi.org/10.1186/s13068-019-1556-y

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Abstract

BackgroundMyceliophthora thermophila is a thermophilic ascomycete fungus that is used as a producer of enzyme cocktails used in plant biomass saccharification. Further development of this species as an industrial enzyme factory requires a detailed understanding of its regulatory systems driving the production of plant biomass-degrading enzymes. In this study, we analyzed the function of MtXlr1, an ortholog of the (hemi-)cellulolytic regulator XlnR first identified in another industrially relevant fungus, Aspergillus niger.ResultsThe Mtxlr1 gene was deleted and the resulting strain was compared to the wild type using growth profiling and transcriptomics. The deletion strain was unable to grow on xylan and d-xylose, but showed only a small growth reduction on l-arabinose, and grew similar to the wild type on Avicel and cellulose. These results were supported by the transcriptome analyses which revealed reduction of genes encoding xylan-degrading enzymes, enzymes of the pentose catabolic pathway and putative pentose transporters. In contrast, no or minimal effects were observed for the expression of cellulolytic genes.ConclusionsMyceliophthora thermophila MtXlr1 controls the expression of xylanolytic genes and genes involved in pentose transport and catabolism, but has no significant effects on the production of cellulases. It therefore resembles more the role of its ortholog in Neurospora crassa, rather than the broader role described for this regulator in A. niger and Trichoderma reesei. By revealing the range of genes controlled by MtXlr1, our results provide the basic knowledge for targeted strain improvement by overproducing or constitutively activating this regulator, to further improve the biotechnological value of M. thermophila.

Highlights

Myceliophthora thermophila is a thermophilic ascomycete fungus that is used as a producer of enzyme cocktails used in plant biomass saccharification
In this paper we focus on the xylanolytic activator XlnR (Xyr1/Xlr1), which far is the most extensively studied transcription factor involved in lignocellulose degradation in ascomycete filamentous fungi
To determine whether deletion of Mtxyr1 has an effect on uptake of d-xylose and l-arabinose, the wild-type and ΔMtxyr1 were pre-grown in minimal medium with d-fructose for 48 h in liquid shake flask cultures and aliquots of mycelium were transferred to shake flask cultures with l-arabinose or d-xylose. d-xylose and l-arabinose concentrations were measured in the extracellular medium over time (Fig. 2)

Summary

Introduction

Myceliophthora thermophila is a thermophilic ascomycete fungus that is used as a producer of enzyme cocktails used in plant biomass saccharification. Applying thermostable enzymes in lignocellulose saccharification may lead to a decrease in enzyme dosage, faster conversion rates and higher sugar yields, reducing the overall production costs Myceliophthora thermophila is such a thermophilic ascomycete fungus, which is soilborne and occurs in self-heated compost [10]. This powerful potential for lignocellulose conversion has been shown when the fungus was grown on various untreated agricultural substrates [10, 19,20,21] and on pretreated plant biomass [19, 22] For this reason, the industrial M. thermophila strain C1 was developed into an enzyme production platform, optimized for commercialscale production of xylanolytic and cellulolytic enzymes to release both C5 and C6 sugars efficiently [23]

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