Purification and properties of a basic endo-beta-1,6-glucanase (BGN16.1) from the antagonistic fungus Trichoderma harzianum

Antifungal characterizations of a novel endo-β-1,6-glucanase from Flavobacterium sp. NAU1659

β-1,6-Glucan plays a crucial role in fungal cell walls by linking the outer layer of mannoproteins and the inner layer of β-1,3-glucan, contributing significantly to the maintenance of cell wall rigidity. Therefore, the hydrolysis of β-1,6-glucan by β-1,6-glucanase directly leads to the disintegration of the fungal cell wall. Here, a novel β-1,6-glucanase FlGlu30 was identified from the endophytic Flavobacterium sp. NAU1659 and heterologously expressed in Escherichia coli BL21 (DE3). The optimal reaction conditions of purified FlGlu30 were 50℃ and pH 6.0, resulting in a specific activity of 173.1 U/mg using pustulan as the substrate. The hydrolyzed products of FlGlu30 to pustulan were mainly gentianose within 1 h of reaction. With the extension of reaction time, gentianose was gradually hydrolyzed to glucose, indicating that FlGlu30 is an endo-β-1,6-glucanase. The germination of Magnaporthe oryzae Guy11 spores could not be inhibited by FlGlu30, but the appressorium formation of spores was completely inhibited under the concentration of 250.0 U/mL FlGlu30. The disruptions of cell wall and accumulation of intracellular reactive oxide species (ROS) were observed in FlGlu30-treated M. oryzae Guy11 cells, suggesting the significant importance of β-1,6-glucan as a potential antifungal target and the potential application of FlGlu30. KEY POINTS: • β-1,6-Glucan is a key component maintaining the rigid structure of fungal cell wall. • β-1,6-Glucanase is an antifungal protein with significant potential applications. • FlGlu30 is the first reported β-1, 6-glucanase derived from Flavobacterium.

Functional analysis of a novel endo-β-1,6-glucanase MoGlu16 and its application in detecting cell wall β-1,6-glucan of Magnaporthe oryzae

As an essential component of the fungal cell wall, β-1,6-glucan has an important role in the growth and development of fungi, but its distribution has not been investigated in Magnaporthe oryzae. Here, a novel β-1,6-glucanase from M. oryzae, MoGlu16, was cloned and expressed in Pichia pastoris. The enzyme was highly active on pustulan, with a specific activity of 219.0 U/mg at pH 5.0 and 50°C, and showed great selectivity for continuous β-1,6-glycosidic bonding polysaccharides. Based on this, β-1,6-glucan was selectively visualized in the vegetative hyphae, conidia and bud tubes of M. oryzae using a hydrolytically inactive GFP-tagged MoGlu16 with point mutations at the catalytic position (His-MoGlu16E236A-Gfp). The spore germination and appressorium formation were significantly inhibited after incubation of 105/ml conidia with 0.03 μg/μl MoGlu16. Mycelia treated with MoGlu16 produced reactive oxygen species and triggered the cell wall integrity pathway, increasing the expression levels of genes involved in cell wall polysaccharide synthesis. These results revealed that MoGlu16 participated in the remodeling of cell wall in M. oryzae, laying a foundation for the analysis of cell wall structure.

Strain improvement of Trichoderma harzianum for enhanced biocontrol capacity: Strategies and prospects

In the control of plant diseases, biocontrol has the advantages of being efficient and safe for human health and the environment. The filamentous fungus Trichoderma harzianum and its closely related species can inhibit the growth of many phytopathogenic fungi, and have been developed as commercial biocontrol agents for decades. In this review, we summarize studies on T. harzianum species complex from the perspective of strain improvement. To elevate the biocontrol ability, the production of extracellular proteins and compounds with antimicrobial or plant immunity-eliciting activities need to be enhanced. In addition, resistance to various environmental stressors should be strengthened. Engineering the gene regulatory system has the potential to modulate a variety of biological processes related to biocontrol. With the rapidly developing technologies for fungal genetic engineering, T. harzianum strains with increased biocontrol activities are expected to be constructed to promote the sustainable development of agriculture.

Use of the volatile trichodiene to reduce Fusarium head blight and trichothecene contamination in wheat

Fusarium graminearum is the primary cause of Fusarium head blight (FHB), one of the most economically important diseases of wheat worldwide. FHB reduces yield and contaminates grain with the trichothecene mycotoxin deoxynivalenol (DON), which poses a risk to plant, human and animal health. The first committed step in trichothecene biosynthesis is formation of trichodiene (TD). The volatile nature of TD suggests that it could be a useful intra or interspecies signalling molecule, but little is known about the potential signalling role of TD during F. graminearum-wheat interactions. Previous work using a transgenic Trichoderma harzianum strain engineered to emit TD (Th + TRI5) indicated that TD can function as a signal that can modulate pathogen virulence and host plant resistance. Herein, we demonstrate that Th + TRI5 has enhanced biocontrol activity against F. graminearum and reduced DON contamination by 66% and 70% in a moderately resistant and a susceptible cultivar, respectively. While Th + TRI5 volatiles significantly influenced the expression of the pathogenesis-related 1 (PR1) gene, the effect was dependent on cultivar. Th + TRI5 volatiles strongly reduced DON production in F. graminearum plate cultures and downregulated the expression of TRI genes. Finally, we confirm that TD fumigation reduced DON accumulation in a detached wheat head assay.

Fungus-originated glucanase and monooxygenase genes in creeping bent grass (Agrostis stolonifera L.)

Recent studies have revealed presence of fungus-originated genes in genomes of cool-season grasses, suggesting occurrence of multiple ancestral gene transfer events between the two distant lineages. The current article describes identification of glucanase-like and monooxygenase-like genes from creeping bent grass, as lateral gene transfer candidates. An in silico analysis suggested presence of the glucanase-like gene in Agrostis, Deyeuxia, and Polypogon genera, but not in other species belonging to the clade 1 of the Poeae tribe. Similarly, the monooxygenase-like gene was confined to Agrostis and Deyeuxia genera. A consistent result was obtained from PCR-based screening. The glucanase-like gene was revealed to be ubiquitously expressed in young seedlings of creeping bent grass. Although expression of the monooxygenase-like gene was suggested in plant tissues, the levels were considerably lower than those of the glucanase-like gene. A phylogenetic analysis revealed close relationships of the two genes between the corresponding genes in fungal endophyte species of the Epichloë genus, suggesting that the genes originated from the Epichloë lineage.

Heterologous expression and characterization of a novel glycoside hydrolase family 55 β-1,3-glucanase, AcGluA, from Archangium sp. strain AC19

Some microbial-associated molecular patterns (MAMPs), like glucan oligosaccharides, can be recognized by pattern recognition receptors (PRRs) of plant to elicit further immunity response. In this study, a novel glycoside hydrolase family 55 β-1,3-glucanase (AcGluA) from Archangium sp. strain AC19 was cloned and expressed in Escherichia coli. Among the reported β-1, 3-glucanases from the glycoside hydrolase 55 family, the purified AcGluA exhibited the highest activity on laminarin at pH 6.0 and 60 °C with 112.3 U/mg. Activity of AcGluA was stable in the range of pH 4.0-9.0 and at temperatures below 60 °C. The K_m and V_max of AcGluA for laminarin were 3.5 mg/ml and 263.5 μmol/(ml·min). AcGluA hydrolyzed laminarin into a series of oligosaccharides, suggesting it was an endo-β-1,3-glucanase. The high dose of oligosaccharides (1600 mg/l) had conspicuous biocontrol efficacy on the defense of rice seedlings to Magnaporthe oryzae, which provided a new idea for the development of green biopesticide.Key points• The AcGluA was determined bacteria-derived β-1,3-glucanases in the GH55 family.• The AcGluA showed the highest activity towards laminarin among reported GH55 family.• The hydrolysates of laminarin showed conspicuous biocontrol efficacy to M. oryzae.

Properties of recombinant endo-β-1,6-glucanase from Trichoderma harzianum and its application in the pustulan hydrolysis

The gene encoding Trichoderma harzianum fungus pustulanase (ThBGL1.6, GH5 family, endo-β-1,6-glucanase, EC 3.2.1.75) was cloned and heterologously expressed by the highly productive Penicillium verruculosum fungus. The recombinant ThBGL1.6 was purified and its properties were studied. The ThBGL1.6 had an observed molecular mass of 46 kDa (SDS-PAGE data) and displayed maximum of the enzyme activity at pH 5.0 and 50 °C. At 45 °C, the ThBGL1.6 was stable for at least 3 h. The K_m was 1.0 g/L with pustulan as the substrate. Reaction product analysis by HPLC clearly indicated that ThBGL1.6 has an endo-hydrolytic mode of action against pustulan as specific substrate. It was also identified that gentiobiose is the main reaction product at studying of long-term pustulan hydrolysis.

Molecular characterization of β-endoglucanase from antagonistic Trichoderma saturnisporum isolate GITX-Panog (C) induced under mycoparasitic conditions

The endoglucanase belonging to glycoside hydrolase family 61 are little studied. In present study, a β-endoglucanase of ~37 kDa induced on autoclaved mycelium of Fusarium oxysporum was cloned and characterized. The molecular characterization of β-endoglucanase encoding gene revealed presence of a single intron and an open reading frame of 1044-bp which encoded a protein of 347 amino acid residues. The phylogenetic analysis of Eglu revealed its similarity to endo-β-glucanases of other Trichoderma spp. The catalytic site of β-endoglucanase contained Asp, Asn, His and Tyr residues. The cDNA encoding β-glucanase was cloned into E. coli and Pichia pastoris using pQUA-30 and pPIC9K vector system, respectively. The comparison of structure revealed that most similar structure to Eglu is Hypocrea jecorina template 5o2w.1.A of glycoside hydrolase family 61.The biochemical characterization of β-endoglucanase purified from T. saturnisporum isolate and the recombinant protein expressed in E. coli and P. pastoris was active under acidic conditions with a pH optima of 5 and temperature optima of 60 °C. The purified and expressed enzyme preparation was able to inhibit growth of F.oxysporum at 1 × 10⁵ spores/mL which clearly revealed its significance in plant pathogen suppression.

Biochemical Characterization of Recombinant Thermostable Cohnella sp. A01 β-Glucanase

Background

Typically, non-cellulytic glucanase, including fungi and yeast cell wall hydrolyzing enzymes, are released by some symbiotic fungi and plants during the mycoparasitic fungi attack on plants. These enzymes are known as the defense mechanisms of plants. This study intends to investigate the biochemical properties of β-1,6-glucanase (bg16M) from native thermophilic bacteria, Cohnella A01.

Methods

bg16M gene was cloned and expressed in E. coli BL21 (DE3). The enzyme was purified utilizing Ni-NTA nikcle sepharose column. Pustulan and laminarin were selected as substrates in enzyme assay. The purified bg16M enzyme was treated with different pH, temperature, metal ions, and detergents.

Results

The expressed protein, including 639 amino acids, showed a high similarity with the hydrolytic glycosylated family 30. The molecular weight of enzyme was 64 kDa, and purification yield was 46%. The bg16M demonstrated activity as 4.83 U/ml on laminarin and 2.88 U/ml on pustulan. The optimum pH and temperature of the enzyme were 8 and 50 °C, respectively. The enzyme had an appropriate stability at high temperatures and in the pH range of 7 to 9, showing acceptable stability, while it did not lose enzymatic activity completely at acidic or basic pH. None of the studied metal ions and chemical compounds was the activator of bg16M, and urea, SDS, and copper acted as enzyme inhibitors.

Conclusion

Biochemical characterization of this enzyme revealed that bg16M can be applied in beverage industries and medical sectors because of its high activity, as well as thermal and alkaline stability.

Isolation and characterization of the bioactive metabolites from the soil derived fungus Trichoderma viride

The aim of the present study was to evaluate different biological activities of Trichoderma viride fungus (Family Hypocreaceae). Trichoderma viride isolated for the first time from the cucumber soil (rhizosphere). It was tested as antimicrobial, antioxidant and anticancer agent. Trichoderma viride from the cucumber soil (rhizosphere) caused inhibition of the mycelial growth of Fusarium solani, Rhizoctonia solani and Sclerotium rolfsii. Also, the alcoholic extract of the fungal mycelia proved a potent antibacterial activity against Bacillus subtilis, Escherichia coli and Pseudomonas fluorescens. In addition, it exhibited a significant antifungal activity against Candida albicans, Fusarium solani, Fusarium oxysporium, Rhizoctonia solani and Pythium ultimum at 100 µg/disc. Study of the antimicrobial and antioxidant activities of the volatile constituents had been done. The in vitro antioxidant, anticancer and antiviral activities of the isolated proteins, and carbohydrates were determined. Furthermore, the volatile constituents were isolated from fresh mycelia of Trichoderma viride and subjected to GC/MS analysis. Total protein (10%), carbohydrate (19.57%), steroidal (13.95%) and triterpenoidal content (38.34%) were determined in the alcoholic extract of Trichoderma viride mycelia. In conclusion, this fungus showed antioxidant, anticancer, antiviral and antibacterial effects. Further studies must be done to identify the molecules responsible for its effect and to consider its application in the pharmacological and medicinal purposes.

Integrated Translatome and Proteome: Approach for Accurate Portraying of Widespread Multifunctional Aspects of Trichoderma

Genome-wide studies of transcripts expression help in systematic monitoring of genes and allow targeting of candidate genes for future research. In contrast to relatively stable genomic data, the expression of genes is dynamic and regulated both at time and space level at different level in. The variation in the rate of translation is specific for each protein. Both the inherent nature of an mRNA molecule to be translated and the external environmental stimuli can affect the efficiency of the translation process. In biocontrol agents (BCAs), the molecular response at translational level may represents noise-like response of absolute transcript level and an adaptive response to physiological and pathological situations representing subset of mRNAs population actively translated in a cell. The molecular responses of biocontrol are complex and involve multistage regulation of number of genes. The use of high-throughput techniques has led to rapid increase in volume of transcriptomics data of Trichoderma. In general, almost half of the variations of transcriptome and protein level are due to translational control. Thus, studies are required to integrate raw information from different “omics” approaches for accurate depiction of translational response of BCAs in interaction with plants and plant pathogens. The studies on translational status of only active mRNAs bridging with proteome data will help in accurate characterization of only a subset of mRNAs actively engaged in translation. This review highlights the associated bottlenecks and use of state-of-the-art procedures in addressing the gap to accelerate future accomplishment of biocontrol mechanisms.

Horizontal transfer of a ß-1,6-glucanase gene from an ancestral species of fungal endophyte to a cool-season grass host

Molecular characterisation has convincingly demonstrated some types of horizontal gene transfer in eukaryotes, but nuclear gene transfer between distantly related eukaryotic groups appears to have been rare. For angiosperms (flowering plants), nuclear gene transfer events identified to date have been confined to genes originating from prokaryotes or other plant species. In this report, evidence for ancient horizontal transfer of a fungal nuclear gene, encoding a ß-1,6-glucanase enzyme for fungal cell wall degradation, into an angiosperm lineage is presented for the first time. The gene was identified from de novo sequencing and assembly of the genome and transcriptome of perennial ryegrass, a cool-season grass species. Molecular analysis confirmed the presence of the complete gene in the genome of perennial ryegrass. No corresponding sequence was found in other plant species, apart from members of the Poeae sub-tribes Loliinae and Dactylidinae. Evidence suggests that a common ancestor of the two sub-tribes acquired the gene from a species ancestral to contemporary grass-associated fungal endophytes around 9-13 million years ago. This first report of horizontal transfer of a nuclear gene from a taxonomically distant eukaryote to modern flowering plants provides evidence for a novel adaptation mechanism in angiosperms.

Secretome analysis of the mycoparasitic fungus Trichoderma harzianum ALL 42 cultivated in different media supplemented with Fusarium solani cell wall or glucose

Trichoderma harzianum is a fungus well known for its potential as a biocontrol agent against many fungal phytopathogens. The aim of this study was to characterize the proteins secreted by T. harzianum ALL42 when its spores were inoculated and incubated for 48 h in culture media supplemented with glucose (GLU) or with cell walls from Fusarium solani (FSCW), a phytopathogen that causes severe losses in common bean and soy crops in Brazil, as well as other crop diseases around the world. Trichoderma harzianum was able to grow in Trichoderma Liquid Enzyme Production medium (TLE) and Minimal medium (MM) supplemented with FSCW and in TLE+GLU, but was unable to grow in MM+GLU medium. Protein quantification showed that TLE+FSCW and MM+FSCW had 45- and 30- fold, respectively, higher protein concentration on supernatant when compared to TLE+GLU, and this difference was observable on 2D gel electrophoresis (2DE). A total of 94 out of 105 proteins excised from 2DE maps were identified. The only protein observed in all three conditions was epl1. In the media supplemented with FSCW, different hydrolases such as chitinases, β-1,3-glucanases, glucoamylases, α-1,3-glucanases and proteases were identified, along with other proteins with no known functions in mycoparasitism, such as npp1 and cys. Trichoderma harzianum showed a complex and diverse arsenal of proteins that are secreted in response to the presence of FSCW, with novel proteins not previously described in mycoparasitic-related studies.

Biological control of wood decay against fungal infection

Wood (timber) is an important raw material for various purposes, and having biological composition it is susceptible to deterioration by various agents. The history of wood protection by impregnation with synthetic chemicals is almost two hundred years old. However, the ever-increasing public concern and the new environmental regulations on the use of chemicals have created the need for the development and the use of alternative methods for wood protection. Biological wood protection by antagonistic microbes alone or in combination with (bio)chemicals, is one of the most promising ways for the environmentally sound wood protection. The most effective biocontrol antagonists belong to genera Trichoderma, Gliocladium, Bacillus, Pseudomonas and Streptomyces. They compete for an ecological niche by consuming available nutrients as well as by secreting a spectrum of biochemicals effective against various fungal pathogens. The biochemicals include cell wall-degrading enzymes, siderophores, chelating iron and a wide variety of volatile and non-volatile antibiotics. In this review, the nature and the function of the antagonistic microbes in wood protection are discussed.

An endo-β-1,6-glucanase involved in Lentinula edodes fruiting body autolysis

A β-1,6-glucanase, LePus30A, was purified and cloned from fruiting bodies of the basidiomycete Lentinula edodes. β-1,6-glucanases degrade β-1,6-glucan polysaccharides, a unique and essential component of fungal cell walls. The complementary DNA of LePus30A includes an open reading frame of 1,575 bp encoding an 18 amino acid signal peptide and the 506 amino acid mature protein. Sequence analysis indicated that LePus30A is a member of glycoside hydrolase family 30, and highly similar genes are broadly conserved among basidiomycetes. The purified LePus30A catalyzed depolymerization of β-1,6-glucan endolytically and was highly specific toward β-1,6-glucan polysaccharide. It is known that the cell walls of fruiting bodies of basidiomycetes are autodegraded after harvesting by means of enzymatic hydrolysis. The transcript level of LePus30A gene (lepus30a) was significantly increased in fruiting bodies after harvesting. Moreover, LePus30A showed hydrolyzing activity against the cell wall components of L. edodes fruiting bodies. These results suggest that LePus30A is responsible for the degradation of the cell wall components during fruiting body autolysis after harvest.

Heterologous expression and characterization of a beta-1,6-glucanase from Aspergillus fumigatus

The cell wall of Candida albicans is composed of mannoproteins associated to glycan polymers. Most of these proteins are retained in this compartment through a phosphodiester linkage between a remnant of their glycosylphosphatidylinositol anchor and the beta-1,6-glucan polymer. A pure beta-1,6-glucanase is thus required in order to release them. In this paper, we report the expression/secretion by the yeast Yarrowia lipolytica of an Aspergillus fumigatus enzyme homologous to previously described beta-1,6-glucanases. The coding sequence was expressed under the control of a strong promoter and the recombinant enzyme was targeted to the secretory pathway using the signal sequence of a well-known major secretory protein in this host. Addition of a FLAG epitope at the C-terminus allowed its efficient purification from culture supernatant following batch adsorption. The purified enzyme was characterized as a beta-1,6-glucanase and was shown to be active on C. albicans cell walls allowing the release of a previously described cell wall protein.

Proteomic study of biocontrol mechanisms of Trichoderma harzianum ETS 323 in response to Rhizoctonia solani

To elucidate the entire range of proteins that are secreted by Trichoderma harzianum ETS 323 in its antagonism with Rhizoctonia solani, an in vivo interaction between them was mimicked and not only the secreted cell wall-degrading enzymes (CWDEs) but also all of the proteome were investigated. Seven CWDEs, chitinase, cellulase, xylanase, beta-1,3-glucanase, beta-1,6-glucanase, mannanase, and protease,were revealed by activity assay, in-gel activity stain, 2-DE, and LC-MS/MS analysis. Extracellular protein extracts from media that contained R. solani exhibited much higher CWDE activities than media that did not contain R. solani. Cellulase and mannanase activity, however, were insignificant. Activity stain also revealed that beta-1,3-glucanase, beta-1,6-glucanase, and xylanase activity occurred exclusively in media that contained R. solani. Furthermore, 35 of the 43 excised spots on the 2-DE gel were successfully analyzed by LC-MS/MS, and eight proteins were identified. They were two glycoside hydrolases, two proteases, two beta-glucosidases, one endochitinase and, interestingly, one amino acid oxidase. Additionally, a possible mechanism was proposed to elucidate how the cell walls of R. solani are systematically enveloped and disintegrated.

Cloning and characterization ofbgn16·3, coding for a β-1,6-glucanase expressed duringTrichoderma harzianummycoparasitism

AIMS

To clone and characterize the gene coding for BGN16.3, a beta-1,6-glucanase putatively implicated in mycoparasitism by Trichoderma harzianum, a biocontrol agent used against plant pathogenic fungi.

METHODS AND RESULTS

Using degenerate primed PCR and cDNA library screening, we have cloned the cDNA coding BGN16.3. bgn16.3 showed a significant sequence identity (50%) to bgn16.1; however, they both have low identity to the previously cloned bgn16.2, allowing the identification of amino acid sequences putatively involved in the common catalytic activity of the three proteins. bgn16.3 is a single-copy gene and highly homologous sequences are present in all tested Trichoderma species. bgn16.3 expression pattern is analysed by Northern blot, finding that it is expressed during the interaction of T. harzianum CECT 2413 with Botrytis cinerea, supporting the implication of the enzyme in the mycoparasitic process.

CONCLUSIONS

The cloned bgn16.3 completes the knowledge on the beta-1,6-glucanase isozyme system from T. harzianum CECT 2413. A highly homologous gene is present in all analysed Trichoderma strains. bgn16.3 is expressed under few specific conditions, including the mycoparasitic process.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study contributes to the knowledge of beta-1,6-glucanases. It implicates this group of enzymes in the mycoparasitism by some biocontrol agents such as T. harzianum.

Functional analysis of a β-1,6-glucanase gene from the grass endophytic fungus Epichloë festucae

beta-1,6-glucanases degrade the polysaccharide beta-1,6-glucan, a cell wall component in some filamentous fungi. A single copy of a beta-1,6-glucanase gene, designated gcnA, was identified in each of the grass endophytic fungi Neotyphodium lolii and Epichloë festucae. Phylogenetic analysis indicates that the GcnA protein is a member of glycosyl hydrolase family 5, and is closely related to fungal beta-1,6-glucanases implicated in mycoparasitism. The E. festucae gcnA gene was expressed in mycelium grown in culture and in both vegetative and reproductive tissues of perennial ryegrass. A gcnA replacement mutant had reduced beta-1,6-glucanase activity when grown in media containing pustulan as the major carbon source. beta-1,6-glucanase activity was restored in the replacement mutant by introducing multiple copies of the gcnA gene. Growth of DeltagcnA and gcnA-overexpressing strains in vegetative grass tissues was indistinguishable from wild type strains.

Partial silencing of a hydroxy-methylglutaryl-CoA reductase-encoding gene in Trichoderma harzianum CECT 2413 results in a lower level of resistance to lovastatin and lower antifungal activity

In the present article, we describe the cloning and characterization of the Trichoderma harzianum hmgR gene encoding a hydroxymethylglutaryl CoA reductase (HMGR), a key enzyme in the biosynthesis of terpene compounds. In T. harzianum, partial silencing of the hmgR gene gave rise to transformants with a higher level of sensitivity to lovastatin, a competitive inhibitor of the HMGR enzyme. In addition, these hmgR-silenced transformants produced lower levels of ergosterol than the wild-type strain in a minimal medium containing lovastatin. The silenced transformants showed a decrease in hmgR gene expression (up to a 8.4-fold, after 72h of incubation), together with an increase in the expression of erg7 (up to a 15.8-fold, after 72h of incubation), a gene involved in the biosynthesis of triterpenes. Finally, hmgR-silenced transformants showed a reduction in their antifungal activity against the plant-pathogen fungi Rhizoctonia solani and Fusarium oxysporum.

Biochemistry and molecular biology of exocellular fungal beta-(1,3)- and beta-(1,6)-glucanases

Many fungi produce exocellular beta-glucan-degrading enzymes, the beta-glucanases including the noncellulolytic beta-(1,3)- and beta-(1,6)-glucanases, degrading beta-(1,3)- and beta-(1,6)-glucans. An ability to purify several exocellular beta-glucanases attacking the same linkage type from a single fungus is common, although unlike the beta-1,3-glucanases, production of multiple beta-1,6-glucanases is quite rare in fungi. Reasons for this multiplicity remain unclear and the multiple forms may not be genetically different but arise by posttranslational glycosylation or proteolytic degradation of the single enzyme. How their synthesis is regulated, and whether each form is regulated differentially also needs clarifying. Their industrial potential will only be realized when the genes encoding them are cloned and expressed in large quantities. This review considers what is known in molecular terms about their multiplicity of occurrence, regulation of synthesis and phylogenetic diversity. It discusses how this information assists in understanding their functions in the fungi producing them. It deals largely with exocellular beta-glucanases which here refers to those recoverable after the cells are removed, since those associated with fungal cell walls have been reviewed recently by Adams (2004). It also updates the earlier review by Pitson et al. (1993).

Tvbgn3, a beta-1,6-glucanase from the biocontrol fungus Trichoderma virens, is involved in mycoparasitism and control of Pythium ultimum

Even though beta-1,6-glucanases have been purified from several filamentous fungi, the physiological function has not been conclusively established for any species. In the present study, the role of Tvbgn3, a beta-1,6-glucanase from Trichoderma virens, was examined by comparison of wild-type (WT) and transformant strains in which Tvbgn3 was disrupted (GKO) or constitutively overexpressed (GOE). Gene expression analysis revealed induction of Tvbgn3 in the presence of host fungal cell walls, indicating regulation during mycoparasitism. Indeed, while deletion or overexpression of Tvbgn3 had no evident effect on growth and development, GOE and GKO strains showed an enhanced or reduced ability, respectively, to inhibit the growth of the plant pathogen Pythium ultimum compared to results with the WT. The relevance of this activity in the biocontrol ability of T. virens was confirmed in plant bioassays. Deletion of the gene resulted in levels of disease protection that were significantly reduced from WT levels, while GOE strains showed a significantly increased biocontrol capability. These results demonstrate the involvement of beta-1,6-glucanase in mycoparasitism and its relevance in the biocontrol activity of T. virens, opening a new avenue for biotechnological applications.

Crystal structure at 1.45-Å resolution of the major allergen endo-β-1,3-glucanase of banana as a molecular basis for the latex-fruit syndrome

Resolution of the crystal structure of the banana fruit endo-beta-1,3-glucanase by synchrotron X-ray diffraction at 1.45-A resolution revealed that the enzyme possesses the eightfold beta/alpha architecture typical for family 17 glycoside hydrolases. The electronegatively charged catalytic central cleft harbors the two glutamate residues (Glu94 and Glu236) acting as hydrogen donor and nucleophile residue, respectively. Modeling using a beta-1,3 linked glucan trisaccharide as a substrate confirmed that the enzyme readily accommodates a beta-1,3-glycosidic linkage in the slightly curved catalytic groove between the glucose units in positions -2 and -1 because of the particular orientation of residue Tyr33 delimiting subsite -2. The location of Phe177 in the proximity of subsite +1 suggested that the banana glucanase might also cleave beta-1,6-branched glucans. Enzymatic assays using pustulan as a substrate demonstrated that the banana glucanase can also cleave beta-1,6-glucans as was predicted from docking experiments. Similar to many other plant endo-beta-1,3-glucanases, the banana glucanase exhibits allergenic properties because of the occurrence of well-conserved IgE-binding epitopes on the surface of the enzyme. These epitopes might trigger some cross-reactions toward IgE antibodies and thus account for the IgE-binding cross-reactivity frequently reported in patients with the latex-fruit syndrome.

BGN16.3, a novel acidic β-1,6-glucanase from mycoparasitic fungus Trichoderma harzianum CECT 2413

A new component of the beta-1,6-glucanase (EC 3.2.1.75) multienzymatic complex secreted by Trichoderma harzianum has been identified and fully characterized. The protein, namely BGN16.3, is the third isozyme displaying endo-beta-1,6-glucanase activity described up to now in T. harzianum CECT 2413. BGN16.3 is an acidic beta-1,6-glucanase that is specifically induced by the presence of fungal cell walls in T. harzianum growth media. The protein was purified to electrophoretical homogenity using its affinity to beta-1,6-glucan as first purification step, followed by chomatofocusing and gel filtration. BGN16.3 has a molecular mass of 46 kDa in SDS/PAGE and a pI of 4.5. The enzyme only showed activity against substrates with beta-1,6-glycosidic linkages, and it has an endohydrolytic mode of action as shown by HPLC analysis of the products of pustulan hydrolysis. The expression profile analysis of BGN16.3 showed a carbon source control of the accumulation of the enzyme, which is fast and strongly induced by fungal cell walls, a condition often regarded as mycoparasitic simulation. The likely involvement beta-1,6-glucanases in this process is discussed.

Detection of putative peptide synthetase genes inTrichodermaspecies: Application of this method to the cloning of a gene fromT. harzianumCECT 2413

Some of the secondary metabolites produced by Trichoderma, such as the peptaibols and other antibiotics, have a peptide structure and in their biosynthesis are involved proteins belonging to the Non-Ribosomal Peptide Synthetase family. In the present work, a PCR-mediated strategy was used to clone a region corresponding to an adenylation domain of a peptide synthetase (PS) gene from 10 different strains of Trichoderma. In addition, and using the fragment isolated by PCR from T. harzianum CECT 2413 as a probe, a fragment of 19.0 kb corresponding to a PS-encoding gene named salps1, including a 1.5 kb fragment of the promoter, was cloned and sequenced. The cloned region of salps1 contains four complete, and a fifth incomplete, modules, in which are found the adenylation, thiolation and condensation domains, but also an additional epimerization domain at the C-terminal end of the first module. The analysis of the Salps1 protein sequence, taking into consideration published data, suggests that it is neither a peptaibol synthetase nor a protein involved in siderophore biosynthesis. The presence of two breaks in the open reading frame and the expression of this gene under nitrogen starvation conditions suggest that salps1 could be a pseudogene.

Specific PCR assays for the detection and quantification of DNA from the biocontrol strain Trichoderma harzianum 2413 in soil

Strain identification in situ is an important factor in the monitoring of microorganisms used in the field. In this study, we demonstrated the use of sequence-characterized amplified region (SCAR) markers to detect genomic DNA from Trichoderma harzianum 2413 from soil. Two primers (SCAR A1/SCAR A1c) were tested against DNA of 27 isolates of Trichoderma spp. and amplified a 990-bp fragment from T. atroviride 11 and a 1.5-kb fragment from T. harzianum 2413, using an annealing temperature of 68 degrees C. These fragments showed no significant homology to any sequence deposited in the databases. The primer pair, BR1 and BR2, was designed to the 1.5-kb fragment amplified from T. harzianum 2413, generating a SCAR marker. To test the specificity of these primers, experiments were conducted using the DNA from 27 Trichoderma spp. strains and 22 field soil samples obtained from four different countries. PCR results showed that BR1 and BR2 amplified an 837-bp fragment unique to T. harzianum 2413. Assays in which total DNA was extracted from sterile and nonsterile soil samples, inoculated with spore or mycelium combinations of Trichoderma spp. strains, indicated that the BR1 and BR2 primers could specifically detect T. harzianum 2413 in a pool of mixed DNA. No other soil-microorganisms containing these sequences were amplified using these primers. To test whether the 837-bp SCAR marker of T. harzianum 2413 could be used in real-time PCR experiments, new primers (Q2413f and Q2413r) conjugated with a TaqMan fluorogenic probe were designed. Real-time PCR assays were applied using DNA from sterile and nonsterile soil samples inoculated with a known quantity of spores of Trichoderma spp. strains.

Endophytic fungal beta-1,6-glucanase expression in the infected host grass

Mutualistic fungal endophytes infect many grass species and often confer benefits to the hosts such as reduced herbivory by insects and animals. The physiological interactions between the endophytes and their hosts have not been well characterized. Fungal-secreted proteins are likely to be important components of the interaction. In the interaction between Poa ampla and the endophyte Neotyphodium sp., a fungal beta-1,6-glucanase is secreted into the apoplast, and activity of the enzyme is detectable in endophyte-infected plants. Sequence analysis indicates the beta-1,6-glucanase is homologous to enzymes secreted by the mycoparasitic fungi Trichoderma harzianum and Trichoderma virens. DNA gel-blot analysis indicated the beta-1,6-glucanase was encoded by a single gene. As a secreted protein, the beta-1,6-glucanase may have a nutritional role for the fungus. In culture, beta-1,6-glucanase activity was induced in the presence of beta-1,6-glucans. From RNA gel blots, similar beta-1,6-glucanases were expressed in tall fescue (Festuca arundinacea Schreb.) and Chewings fescue (Festuca rubra L. subsp. fallax [Thuill] Nyman) infected with the endophyte species Neotyphodium coenophialum and Epichloë festucae, respectively.

Purification and characterization of beta-1,6-glucanase of Streptomyces rochei application in the study of yeast cell wall proteins

A beta-1,6-glucanase was purified to apparent homogeneity from a commercial yeast digestive enzyme prepared from Streptomyces rochei by a series of column chromatographies. The molecular mass of the purified enzyme was 60 kDa by SDS-PAGE. The purified enzyme had an optimum pH range from 4.0 to 6.0 and was stable in the same pH range. The enzyme was stable under 50 degrees C but lost almost all activity at 60 degrees C. The enzyme was specific to beta-1,6-glucan and had little activity towards beta-1,3-glucan and beta-1,4-glucan. When the beta-1,6-glucan was hydrolyzed with the purified enzyme for 5 h, the reaction products contained 20% glucose, 36% gentiobiose, and 44% other oligosaccharides, suggesting that the enzyme is an endo-type glucanase. When the purified enzyme was used for the digestion of the cell wall of Saccharomyces cerevisiae, cell-wall proteins covalently bound to the cell-wall glucan were recovered as soluble forms, suggesting that this enzyme is useful for analysis of yeast-cell wall proteins.

An antifungal exo-alpha-1,3-glucanase (AGN13.1) from the biocontrol fungus Trichoderma harzianum

Trichoderma harzianum secretes alpha-1,3-glucanases when it is grown on polysaccharides, fungal cell walls, or autoclaved mycelium as a carbon source (simulated antagonistic conditions). We have purified and characterized one of these enzymes, named AGN13.1. The enzyme was monomeric and slightly basic. AGN13.1 was an exo-type alpha-1,3-glucanase and showed lytic and antifungal activity against fungal plant pathogens. Northern and Western analyses indicated that AGN13.1 is induced by conditions that simulated antagonism. We propose that AGN13.1 contributes to the antagonistic response of T. harzianum.