Heterologous expression of an endo-β-1,4-glucanase gene from the anaerobic fungus Orpinomyces PC-2 in Trichoderma reesei

Carbohydrate active enzyme system in rumen fungi: a review

Hydrolysis and dehydration reactions of carbohydrates, which are used as energy raw materials by all living things in nature, are controlled by Carbohydrate Active Enzyme (CAZy) systems. These enzymes are also used in different industrial areas today. There are different types of microorganisms that have the CAZy system and are used in the industrial sector. Apart from current organisms, there are also rumen fungi within the group of candidate microorganisms with the CAZy system. It has been reported that xylanase (EC3.2.1.8 and EC3.2.1.37) enzyme, a member of the glycoside hydrolase enzyme family obtained from Trichoderma sp. and used especially in areas such as bread, paper, and feed industry, is more synthesized in rumen fungi such as Orpinomyces sp. and Neocallimastix sp. Therefore, this study reviews Neocallimastixsp., Orpinomyces sp., Caecomyces sp., Piromyces sp., and Anaeromyces sp., registered in the CAZy and Mycocosm database for rumen fungi to have both CAZy enzyme activity and to be an alternative microorganism in the industry. Furthermore the CAZy enzyme activities of the strains are investigated. The review shows thatNeocallimax sp. and Orpinomyces sp. areconsidered as candidate microorganisms.

The Anaerobic Fungi: Challenges and Opportunities for Industrial Lignocellulosic Biofuel Production

Lignocellulose is a promising feedstock for biofuel production as a renewable, carbohydrate-rich and globally abundant source of biomass. However, challenges faced include environmental and/or financial costs associated with typical lignocellulose pretreatments needed to overcome the natural recalcitrance of the material before conversion to biofuel. Anaerobic fungi are a group of underexplored microorganisms belonging to the early diverging phylum Neocallimastigomycota and are native to the intricately evolved digestive system of mammalian herbivores. Anaerobic fungi have promising potential for application in biofuel production processes due to the combination of their highly effective ability to hydrolyse lignocellulose and capability to convert this substrate to H2 and ethanol. Furthermore, they can produce volatile fatty acid precursors for subsequent biological conversion to H2 or CH4 by other microorganisms. The complex biological characteristics of their natural habitat are described, and these features are contextualised towards the development of suitable industrial systems for in vitro growth. Moreover, progress towards achieving that goal is reviewed in terms of process and genetic engineering. In addition, emerging opportunities are presented for the use of anaerobic fungi for lignocellulose pretreatment; dark fermentation; bioethanol production; and the potential for integration with methanogenesis, microbial electrolysis cells and photofermentation.

Combined strategy of transcription factor manipulation and β-glucosidase gene overexpression in Trichoderma reesei and its application in lignocellulose bioconversion

The industrial application of Trichoderma reesei has been greatly limited by insufficient β-glucosidase activity in its cellulase system. In this study, a novel β-glucosidase expression cassette was constructed and integrated at the target site in T. reesei ZU-02, which achieved the overexpression of β-glucosidase gene and in situ disruption of the cellulase transcriptional repressor ACE1. The resulting transformants showed significant increase in both β-glucosidase activity (BGA) and filter paper activity (FPA). The BGA and FPA increased to 25.13 IU/mL and 20.06 FPU/mL, respectively, 167- and 2.45-fold higher than that of the host strain. Meanwhile, the obtained cellulase system exhibited improved ratio of BGA to FPA, leading to better synergistic effect between cellulase components. Furthermore, submerged fermentation of the transformant was established in 50 m3 fermenter yielding 112.2 IU/mL β-glucosidase and 89.76 FPU/mL total cellulase. The newly constructed T. reesei transformant achieved improved hydrolysis yield (90.6%) with reduced enzyme loading (15 FPU/g substrate).

Expression of Talaromyces thermophilus lipase gene in Trichoderma reesei by homologous recombination at the cbh1 locus

CBH1 (cellobiohydrolase) comprises the majority of secreted proteins by Trichoderma reesei. For expression of Talaromyces thermophilus lipase gene in T. reesei, a self-designed CBH1 promoter was applied to drive the lipase gene expression cassette which was bracketed by flanking sequences of cbh1 gene for homologous recombination. Protoplast and Agrobacterium-mediated plasmid transformations were performed and compared, resultantly, transformation mediated by Agrobacterium was overall proved to be more efficient. Stable integration of lipase gene into chromosomal DNA of T. reesei transformants was verified by PCR. After shaking flask fermentation, lipase activity of transformant reached 375 IU mL^-1, whereas no cellobiohydrolase activity was detected. SDS-PAGE analysis further showed an obvious protein band about 39 kDa and no CBH1 band in fermentation broth, implying lipase gene was successfully extracellularly expressed in T. reesei via homologous recombination at cbh1 locus. This study herein would benefit genetic engineering of filamentous fungi and industrial application of thermo-alkaline lipase like in paper making and detergents addition.

Heterologous protein expression in Hypocrea jecorina: a historical perspective and new developments

Hypocrea jecorina, the sexual teleomorph of Trichoderma reesei, has long been favored as an industrial cellulase producer, first utilizing its native cellulase system and later augmented by the introduction of heterologous enzymatic activities or improved variants of native enzymes. Expression of heterologous proteins in H. jecorina was once considered difficult when the target was an improved variant of a native cellulase. Developments over the past nearly 30 years have produced strains, vectors, and selection mechanisms that have continued to simplify and streamline heterologous protein expression in this fungus. More recent developments in fungal molecular biology have pointed the way toward a fundamental transformation in the ease and efficiency of heterologous protein expression in this important industrial host. Here, 1) we provide a historical perspective on advances in H. jecorina molecular biology, 2) outline host strain engineering, transformation, selection, and expression strategies, 3) detail potential pitfalls when working with this organism, and 4) provide consolidated examples of successful cellulase expression outcomes from our laboratory.

High activity cellulase production by recombinant Trichoderma reesei ZU-02 with the enhanced cellobiohydrolase production

The cbh1 strong promoter was employed to over-express the cbh2 gene for enhancing cellobiohydrolase (CBH) production in Trichoderma reesei because CBH II component has higher specific activity than CBH I and is an important component in cellulase. The recombinant plasmid pCAMBIA1300-hph-PsCT containing strong expression cassette was constructed and transformed into T. reesei via optimized Agrobacterium-mediated transformation, producing 324 positive T. reesei transformants for the two steps of screening. Ten fast-growing T. reesei transformants were selected, amongst which C10 was found to have the highest filter paper activity 28.92±2.45 IU/mL, 4.3-fold higher than that of ZU-02, 6.71±0.79 IU/mL. C10 also has the highest cellobiohydrolase activity 122.44±7.42 U/mL, 5.4 times higher than that of ZU-02, 22.49±2.27 U/mL. The cellulase from C10 performed better (93.06±2.83%) than the one from ZU-02 in enzymatic hydrolysis because the exo-exo-synergism played a role.