An overview on current molecular tools for heterologous gene expression in Trichoderma

Recent advances in genetic engineering to enhance plant-polysaccharide-degrading enzyme expression in Penicillium oxalicum: A brief review

With the depletion of non-renewable fossil fuels, there has been an increasing emphasis on renewable biomass. Penicillium oxalicum is notable for its exceptional capacity to secrete a diverse array of enzymes that degrade plant polysaccharides into monosaccharides. These valuable monosaccharides can be harnessed in the production of bioethanol and other sustainable forms of energy. By enhancing the production of plant-polysaccharide-degrading enzymes (PPDEs) in P. oxalicum, we can optimize the utilization of plant biomass. This paper presents recent advances in augmenting PPDE expression in P. oxalicum through genetic engineering strategies involving protoplast preparation, transformation, and factors influencing PPDE gene expression.

Engineered and total biosynthesis of fungal specialized metabolites

Filamentous fungi produce a very wide range of complex and often bioactive metabolites, demonstrating their inherent ability as hosts of complex biosynthetic pathways. Recent advances in molecular sciences related to fungi have afforded the development of new tools that allow the rational total biosynthesis of highly complex specialized metabolites in a single process. Increasingly, these pathways can also be engineered to produce new metabolites. Engineering can be at the level of gene deletion, gene addition, formation of mixed pathways, engineering of scaffold synthases and engineering of tailoring enzymes. Combination of these approaches with hosts that can metabolize low-value waste streams opens the prospect of one-step syntheses from garbage.

Identification of mycoparasitism-related genes in Trichoderma harzianum T4 that are active against Colletotrichum musae

Trichoderma harzianum is a well-known biological control agent (BCA) that shows great potential in controlling many pathogenic fungi. To screen for genes associated with mycoparasitism, we sequenced and analyzed the transcriptome of T. harzianum T4 grown in dual culture with Colletotrichum musae. We analyzed differentially expressed genes (DEGs) of Trichoderma harzianum T4 in three different culture periods: before contact (BC), during contact (C) and after contact (AC). A total of 1453 genes were significantly differentially expressed compared to when T. harzianum T4 was cultured alone. During the three periods of double culture of T. harzianum T4 with C. musae, 74, 516, and 548 genes were up-regulated, respectively, and 11, 315, and 216 genes were down-regulated, respectively. The DEGs were screened using GO and KEGG enrichment analyses combined with differential expression multiples. Six gene categories related to mycoparasitism were screened: (a) pathogen recognition and signal transduction, (b) hydrolases, (c) ribosomal proteins and secreted proteins, (d) multidrug-resistant proteins and transporters, (e) heat shock proteins and detoxification, and (f) oxidative stress and antibiotics-related genes. The expression levels of 24 up-regulated genes during T. harzianum T4's antagonistic interaction with C. musae were detected via real-time fluorescence quantitative PCR (RT-qPCR). This study provided information on the transcriptional expression of T. harzianum T4 against C. musae. These results may help us to further understand the mechanism of mycoparasitism, which can provide a potential molecular target for improving the biological control capacity of T. harzianum T4.

Engineering the metabolism and morphology of the filamentous fungus Trichoderma reesei for efficient L-malic acid production

L-malic acid (MA) is a vital platform chemical with huge market demand because of its broad industrial applications. A cell factory for MA production was engineered by strengthening the intrinsic pathway without inserting foreign genes into Trichoderma reesei. The native MA transporter gene in the T. reesei genome was characterized (trmae1), and its overexpression significantly improved MA production, which increased from 2 to 56.24 g/L. Native pyruvate carboxylase, malate dehydrogenase, malic enzyme, and glucose transporter were overexpressed further to improve the titer and yield of MA production. Fungal morphology was adapted to produce MA in the fermenter by deleting gul1. A titer of 235.8 g/L MA was produced from the final engineered strain in a 5-L fermenter with a yield of 1.48 mol of MA per mol of glucose and productivity of 1.23 g/L/h. This study provides novel insights for understanding and remodeling the MA synthesis pathway.

Heterologous protein production in filamentous fungi

Filamentous fungi are able to produce a wide range of valuable proteins and enzymes for many industrial applications. Recent advances in fungal genomics and experimental technologies are rapidly changing the approaches for the development and use of filamentous fungi as hosts for the production of both homologous and heterologous proteins. In this review, we highlight the benefits and challenges of using filamentous fungi for the production of heterologous proteins. We review various techniques commonly employed to improve the heterologous protein production in filamentous fungi, such as strong and inducible promoters, codon optimization, more efficient signal peptides for secretion, carrier proteins, engineering of glycosylation sites, regulation of the unfolded protein response and endoplasmic reticulum associated protein degradation, optimization of the intracellular transport process, regulation of unconventional protein secretion, and construction of protease-deficient strains. KEY POINTS: • This review updates the knowledge on heterologous protein production in filamentous fungi. • Several fungal cell factories and potential candidates are discussed. • Insights into improving heterologous gene expression are given.

RGS4 impacts carbohydrate and siderophore metabolism in Trichoderma reesei

BACKGROUND

Adaptation to complex, rapidly changing environments is crucial for evolutionary success of fungi. The heterotrimeric G-protein pathway belongs to the most important signaling cascades applied for this task. In Trichoderma reesei, enzyme production, growth and secondary metabolism are among the physiological traits influenced by the G-protein pathway in a light dependent manner.

RESULTS

Here, we investigated the function of the SNX/H-type regulator of G-protein signaling (RGS) protein RGS4 of T. reesei. We show that RGS4 is involved in regulation of cellulase production, growth, asexual development and oxidative stress response in darkness as well as in osmotic stress response in the presence of sodium chloride, particularly in light. Transcriptome analysis revealed regulation of several ribosomal genes, six genes mutated in RutC30 as well as several genes encoding transcription factors and transporters. Importantly, RGS4 positively regulates the siderophore cluster responsible for fusarinine C biosynthesis in light. The respective deletion mutant shows altered growth on nutrient sources related to siderophore production such as ornithine or proline in a BIOLOG phenotype microarray assay. Additionally, growth on storage carbohydrates as well as several intermediates of the D-galactose and D-arabinose catabolic pathway is decreased, predominantly in light.

CONCLUSIONS

We conclude that RGS4 mainly operates in light and targets plant cell wall degradation, siderophore production and storage compound metabolism in T. reesei.

Current genetic strategies to investigate gene functions in Trichoderma reesei

The filamentous fungus Trichoderma reesei (teleomorph Hypocrea jecorina, Ascomycota) is a well-known lignocellulolytic enzymes-producing strain in industry. To increase the fermentation titer of lignocellulolytic enzymes, random mutagenesis and rational genetic engineering in T. reesei were carried out since it was initially found in the Solomon Islands during the Second World War. Especially the continuous exploration of the underlying regulatory network during (hemi)cellulase gene expression in the post-genome era provided various strategies to develop an efficient fungal cell factory for these enzymes' production. Meanwhile, T. reesei emerges competitiveness potential as a filamentous fungal chassis to produce proteins from other species (e.g., human albumin and interferon α-2b, SARS-CoV-2 N antigen) in virtue of the excellent expression and secretion system acquired during the studies about (hemi)cellulase production. However, all the achievements in high yield of (hemi)cellulases are impossible to finish without high-efficiency genetic strategies to analyze the proper functions of those genes involved in (hemi)cellulase gene expression or secretion. Here, we in detail summarize the current strategies employed to investigate gene functions in T. reesei. These strategies are supposed to be beneficial for extending the potential of T. reesei in prospective strain engineering.

Microbial cellulase production and its potential application for textile industries

Purpose

The textile industry’s previous chemical use resulted in thousands of practical particulate emissions, such as machine component damage and drainage system blockage, both of which have practical implications. Enzyme-based textile processing is cost-effective, environmentally friendly, non-hazardous, and water-saving. The purpose of this review is to give evidence on the potential activity of microbial cellulase in the textile industry, which is mostly confined to the realm of research.

Methods

This review was progressive by considering peer-reviewed papers linked to microbial cellulase production, and its prospective application for textile industries was appraised and produced to develop this assessment. Articles were divided into two categories based on the results of trustworthy educational journals: methods used to produce the diversity of microorganisms through fermentation processes and such approaches used to produce the diversity of microbes through microbial fermentation. Submerged fermentation (SMF) and solid-state fermentation (SSF) techniques are currently being used to meet industrial demand for microbial cellulase production in the bio textile industry.

Results

Microbial cellulase is vital for increasing day to day due to its no side effect on the environment and human health becoming increasingly important. In conventional textile processing, the gray cloth was subjected to a series of chemical treatments that involved breaking the dye molecule’s amino group with Cl − , which started and accelerated dye(-resistant) bond cracking. A cellulase enzyme is primarily derived from a variety of microbial species found in various ecological settings as a biotextile/bio-based product technology for future needs in industrial applications.

Conclusion

Cellulase has been produced for its advantages in cellulose-based textiles, as well as for quality enhancement and fabric maintenance over traditional approaches. Cellulase’s role in the industry was microbial fermentation processes in textile processing which was chosen as an appropriate and environmentally sound solution for a long and healthy lifestyle.

Use of CRISPR-Cas tools to engineer Trichoderma species

Given their lignocellulose degradability and biocontrol activities, fungi of the ubiquitously distributed genus Trichoderma have multiple industrial and agricultural applications. Genetic manipulation plays a valuable role in tailoring novel engineered strains with enhanced target traits. Nevertheless, as applied to fungi, the classic tools of genetic manipulation tend to be time-consuming and tedious. However, the recent development of the CRISPR-Cas system for gene editing has enabled researchers to achieve genome-wide gene disruptions, gene replacements, and precise editing, and this technology has emerged as a primary focus for novel developments in engineered strains of Trichoderma. Here, we provide a brief overview of the traditional approaches to genetic manipulation, the different strategies employed in establishing CRSIPR-Cas systems, the utilization of these systems to develop engineered strains of Trichoderma for desired applications, and the future trends in biotechnology.

A novel salt-tolerant strain Trichoderma atroviride HN082102.1 isolated from marine habitat alleviates salt stress and diminishes cucumber root rot caused by Fusarium oxysporum

Background

Salt stress threaten the growth of plants, and even aggravate plant disease. In this article, salt-tolerant Trichoderma strain was isolated, and its potential to alleviate salt stress and diminish cucumber root rot caused by Fusarium oxysporum was evaluated.

Results

Twenty-seven Trichoderma isolates were isolated from samples of sea muds and algae collected from the South Sea of China. Among these, the isolate HN082102.1 showed the most excellent salt tolerance and antagonistic activity against F. oxysporum causing root rot in cucumber and was identified as T. atroviride. Its antagonism ability may be due to mycoparasitism and inhibition effect of volatile substances. The application of Trichoderma mitigated the adverse effects of salt stress and promoted the growth of cucumber under 100 mM and 200 mM NaCl, especially for the root. When T. atroviride HN082102.1 was applied, root fresh weights increased by 92.55 and 84.86%, respectively, and root dry weights increased by 75.71 and 53.31%, respectively. Meanwhile, the application of HN082102.1 reduced the disease index of cucumber root rot by 63.64 and 71.01% under 100- and 0-mM saline conditions, respectively, indicating that this isolate could inhibit cucumber root rot under salt stress.

Conclusions

This is the first report of salt-tolerant T. atroviride isolated from marine habitat showing antagonistic activity to F. oxysporum, and the results provide evidence for the novel strain T. atroviride HN082102.1 in alleviating salt stress and diminishing cucumber root rot, indicating that T. atroviride strain HN082102.1 can be used as biological control agent in saline alkali land.

Engineering multifunctional enzymes for agro-biomass utilization

Lignocellulosic biomass is a plentiful renewable resource that can be converted into a wide range of high-value-added industrial products. However, the complexity of its structural integrity is one of the major constraints and requires combinations of different fibrolytic enzymes for the cost-effective, industrially and environmentally feasible transformation. An interesting approach is constructing multifunctional enzymes, either in a single polypeptide or by joining multiple domains with linkers and performing diverse reactions simultaneously, in a single host. The production of such chimera proteins multiplies the advantages of different enzymatic reactions in a single setup, in lesser time, at lower production cost and with desirable and improved catalytic activities. This review embodies the various domain-tailoring and extracellular secretion strategies, possible solutions to their challenges, and efforts to experimentally connect different catalytic activities in a single host, as well as their applications.