Diversity of Cellulase-Producing Filamentous Fungi From Tibet and Transcriptomic Analysis of a Superior Cellulase Producer Trichoderma harzianum LZ117.

Jia-Xiang Li,Jun Li,Xin-Qing Zhao,Dan-Dan Jiang,Zhang Zhang,Fei Zhang,Feng-Lou Wang,Wei Wang

doi:10.3389/fmicb.2020.01617

Abstract

Filamentous fungi are widely used for producing cellulolytic enzymes to degrade lignocellulosic biomass. Microbial resources from Tibet have received great attention due to the unique geographic and climatic conditions in the Qinghai-Tibet Plateau. However, studies on cellulase producing fungal strains originated from Tibet remain very limited, and so far no studies have been focused on regulation of cellulase production of the specific strains thereof. Here, filamentous fungal strains were isolated from soil, plant, and other environments in Tibet, and cellulase-producing strains were further investigated. A total of 88 filamentous fungal strains were identified, and screening of cellulase-producing fungi revealed that 16 strains affiliated with the genera Penicillium, Trichoderma, Aspergillus, and Talaromyces exhibited varying cellulolytic activities. Among these strains, T. harzianum isolate LZ117 is the most potent producer. Comparative transcriptome analysis using T. harzianum LZ117 and the control strain T. harzianum K223452 cultured on cellulose indicated an intensive modulation of gene transcription related to protein synthesis and quality control. Furthermore, transcription of xyr1 which encodes the global transcriptional activator for cellulase expression was significantly up-regulated. Transcription of cre1 and other predicted repressors controlling cellulase gene expression was decreased in T. harzianum LZ117, which may contribute to enhancing formation of primary cellulases. To our knowledge, this is the first report that the transcription landscape at the early enzyme production stage of T. harzianum was comprehensively described, and detailed analysis on modulation of transporters, regulatory proteins as well as protein synthesis and processing was presented. Our study contributes to increasing the catalog of publicly available transcriptome data from T. harzianum, and provides useful clues for unraveling the biotechnological potential of this species for lignocellulosic biorefinery.

Highlights

Lignocellulose biomass is abundant in nature, and represents more than half of the organic matter produced globally via plant photosynthesis
Industrial cellulase preparations for biomass degradation are generally produced from filamentous fungi (Payne et al, 2015) and comprise a mixture of glycoside hydrolases (GHs) as well as other accessory proteins that are required to work synergistically with cellulases (Champreda et al, 2019)
Fungal cultures were incubated at 28◦C for 3–5 days, and putative filamentous fungal colonies from the primary isolation agar plates were purified by two rounds of subculture on potato-dextrose agar (PDA) and cultured at 28◦C

Summary

Introduction

Lignocellulose biomass is abundant in nature, and represents more than half of the organic matter produced globally via plant photosynthesis. Bioconversion of relatively inexpensive lignocellulosic biomass into biofuels and value-added products can effectively alleviate pressure of energy supply and benefit sustainable development. Industrial cellulase preparations for biomass degradation are generally produced from filamentous fungi (Payne et al, 2015) and comprise a mixture of glycoside hydrolases (GHs) as well as other accessory proteins that are required to work synergistically with cellulases (Champreda et al, 2019). Diversity of cultivable Trichoderma strains in Tibet soil samples and diverse fungal strains from permafrost at Qinghai-Tibet Plateau were reported (Sun et al, 2012; Hu et al, 2014), but cellulase producers were not described. It will be of great interest to explore novel filamentous fungal strains from Tibet for cellulase production and biomass degradation

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Conclusion