Genetic engineering of Trichoderma reesei cellulases and their production

Abstract

SummaryLignocellulosic biomass, which mainly consists of cellulose, hemicellulose and lignin, is the most abundant renewable source for production of biofuel and biorefinery products. The industrial use of plant biomass involves mechanical milling or chipping, followed by chemical or physicochemical pretreatment steps to make the material more susceptible to enzymatic hydrolysis. Thereby the cost of enzyme production still presents the major bottleneck, mostly because some of the produced enzymes have low catalytic activity under industrial conditions and/or because the rate of hydrolysis of some enzymes in the secreted enzyme mixture is limiting. Almost all of the lignocellulolytic enzyme cocktails needed for the hydrolysis step are produced by fermentation of the ascomycete Trichoderma reesei (Hypocreales). For this reason, the structure and mechanism of the enzymes involved, the regulation of their expression and the pathways of their formation and secretion have been investigated in T. reesei in considerable details. Several of the findings thereby obtained have been used to improve the formation of the T. reesei cellulases and their properties. In this article, we will review the achievements that have already been made and also show promising fields for further progress.

Effect of Humicola insolens recombinant endoglucanase on the performance of commercial cellulase in oil palm biomass hydrolysis

“…Celluclast® showed higher affinity to CMC compared with recombinant CMC3 enzyme. The reason may be that Celluclast® contains five different endoglucanases (Gruno et al 2004;Druzhinina and Kubicek, 2017) that can bind to CMC more tightly than CMC3. ISSN (print) The degradation of crystalline cellulose to glucose requires at least three cellulases, such as endoglucanase (EC 3.1.2.4), cellobiohydrolase (exoglucanase) (EC 3.1.2.91) and β-glucosidase (EC 3.1.1.21) (Nazir et al, 2009;Sajith et al, 2016).…”

Upgrading of efficient and scalable CRISPR–Cas-mediated technology for genetic engineering in thermophilic fungus Myceliophthora thermophila

“…In saprophytic fungi, lignocellulolytic enzyme production is mainly regulated at both the transcriptional and post-translational levels which involves combinatorial action of several transcriptional activators and repressors [1,2,[64][65][66][67]. Genetically engineering the regulatory network at both levels, such as overexpression of transcriptional activators and deletion of repressors, represents an efficient and promising strategy for significantly improving cellulases production in cellulolytic fungi including T. reesei, Penicillium oxalicum, N. crassa and M. thermophila [1,7,20,68]. Generally, the cellulase production is induced by cellulose-derived oligosaccharides (e.g., cellobiose) and repressed by preferentially utilized saccharides (e.g., glucose), a phenomenon called carbon catabolite repression (CCR).…”

“…Generally, the cellulase production is induced by cellulose-derived oligosaccharides (e.g., cellobiose) and repressed by preferentially utilized saccharides (e.g., glucose), a phenomenon called carbon catabolite repression (CCR). Therefore, the carbon catabolite repressor CreA/Cre1 is a well-known highly conserved cellulase repressor throughout the fungal kingdom and elimination of the function of CreA/Cre1 resulted in significantly improved lignocellulolytic enzyme production in Aspergillus spp., T. reesei, N. crassa, P. oxalicum and M. thermophila [1,2,7,20,68]. Additionally, elimination of β-glucosidases which hydrolyze cellobiose to glucose is able to improve the expression and production of cellulolytic enzymes.…”

CRZ1 regulator and calcium cooperatively modulate holocellulases gene expression in Trichoderma reesei QM6a

“…Cellulases and hemicellulases are key enzymes for the production of second generation ethanol production worldwide [1]. The promising utilization of agroindustrial residues as energy source has triggered a tremendous interest for engineering microorganisms for the low cost production of these enzymes aiming the conversion of complex plant biomass into fermentable sugars, which in turn could be used for ethanol production [2–4]. In this sense, the saprophyte organism T. reesei is one of the the main filamentous fungus used in industry to produce these enzymes [2].…”

“…The promising utilization of agroindustrial residues as energy source has triggered a tremendous interest for engineering microorganisms for the low cost production of these enzymes aiming the conversion of complex plant biomass into fermentable sugars, which in turn could be used for ethanol production [2–4]. In this sense, the saprophyte organism T. reesei is one of the the main filamentous fungus used in industry to produce these enzymes [2]. Despite the great potential of this fungus for high performance cellulase and hemicellulase production, the regulatory network controlling this system is a relevant field of study and not fully understood yet.…”