Elucidation of ligninolysis mechanism of a newly isolated white-rot basidiomycete Trametes hirsuta X-13

Jiangshan Ma,Yujie Wu,Gao-Qiang Liu,Yanghong Zhang,Huimin Yue,Jiashun Zhang,Qiang Li,Muling Shi,Sixian Wang

doi:10.1186/s13068-021-02040-7

Abstract

BackgroundLignin is a complex aromatic heteropolymer comprising 15–30% dry weight of the lignocellulose. The complex structural characteristic of lignin renders it difficult for value-added utilization. Exploring efficient lignin-degrading microorganisms and investigating their lignin-degradation mechanisms would be beneficial for promoting lignin valorization. In this study, a newly isolated white-rot basidiomycete, Trametes hirsuta X-13, with capacity to utilize alkaline lignin as the sole substrate was investigated.ResultsThe analysis of the fermentation properties of T. hirsuta X-13 using alkaline lignin as the sole substrate, including the mycelial growth, activities of ligninolytic enzymes and the rates of lignin degradation and decolorization confirmed its great ligninolysis capacity. The maximum lignin degradation rate reached 39.8% after 11 days of T. hirsuta X-13 treatment, which was higher than that of reported fungi under the same condition. Fourier transform infrared spectrometry (FTIR), gas chromatography–mass spectrometry (GC–MS) scanning electron micrographs (SEM), two-dimensional heteronuclear single quantum coherence NMR analysis (2D-HSQC NMR) collaborated with pyrolysis gas chromatography–mass spectrometry (py-GC/MS) analyses proved that lignin structure was severely deconstructed along with amounts of monomer aromatics generated. Furthermore, according to those chemical analysis, in addition to canonical Cα–Cβ breakage, the cleavage of lignin interunit linkages of β–β might also occur by T. hirsuta X-13.ConclusionsThis study characterized a newly isolated white-rot basidiomycete T. hirsuta X-13 with impressive alkaline lignin degradation ability and provided mechanistic insight into its ligninolysis mechanism, which will be valuable for the development of lignin valorization strategies.

Highlights

Lignin is a complex aromatic heteropolymer comprising 15–30% dry weight of the lignocellulose
The internal transcribed region sequence (ITS) region sequence of strain X-13 (GenBank: MT995079) showed 99% similarity with that of white-rot basidiomycete Trametes hirsuta JL-22-2 according to NCBI BLAST algorithm analysis
The strain X-13 was identified as Trametes hirsuta strain, which has since been deposited in the China General Microbiological Culture Collection (CGMCC No 18567)

Summary

Introduction

Lignin is a complex aromatic heteropolymer comprising 15–30% dry weight of the lignocellulose. The complex structural characteristic of lignin renders it difficult for value-added utilization. Lignin is a complex aromatic and optically inactive amorphous heteropolymer accounting for 15–30% dry weight of the lignocellulosic biomass, which is the most abundant source of renewable aromatic carbon on earth. It contains three different phenyl propane units (p-hydroxyphenyl, guaiacyl and syringyl units) connected by a multiplicity of C–O and C–C bonds, such as β-O4, β–β, 4-O-5, β-5 [1]. Lignin is embedded between cellulose and hemicellulose structures, forming a complex heterogeneous network that limits the accessibility of enzymes or chemicals [2]. The valorization of lignin by microorganisms which converted it into valuable chemicals such as vanillin, eugenol and other phenolics has attracted much attention [6,7,8]

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