Expression, purification, crystallization and X-ray diffraction studies of a novel root-induced secreted protein from Trichoderma virens

Small secreted cysteine-rich proteins (SSCPs) from fungi play an important role in fungi-host interactions. The plant-beneficial fungi Trichoderma spp. are in use worldwide as biocontrol agents and protect the host plant from soil-borne as well as foliar pathogens. Recently, a novel SSCP, Tsp1, has been identified in the secreted protein pool of T. virens and is overinduced upon its interaction with the roots of the maize plant. The protein was observed to be well conserved in the Ascomycota division of fungi, and its homologs are present in many plant-pathogenic fungi such as Fusarium oxysporum and Magnaporthe oryzae. However, none of these homologs have yet been characterized. Recombinant Tsp1 protein has been expressed and purified using an Escherichia coli expression system. The protein, with four conserved cysteines, forms a dimer in solution as observed by size-exclusion chromatography. The dimerization, however, does not involve disulfide bonds. Circular-dichroism data suggested that the protein has a β-strand-rich secondary structure that matched well with the secondary structure predicted using bioinformatics methods. The protein was crystallized using sodium malonate as a precipitant. The crystals diffracted X-rays to 1.7 Å resolution and belonged to the orthorhombic space group P212121 (Rmeas = 5.4%), with unit-cell parameters a = 46.3, b = 67.0, c = 173.2 Å. The Matthews coefficient (VM) of the crystal is 2.32 Å3 Da-1, which corresponds to nearly 47% solvent content with four subunits of Tsp1 protein in the asymmetric unit. This is the first report of the structural study of any homolog of the novel Tsp1 protein. These structural studies will help in understanding the classification and function of the protein.

New Furan and Cyclopentenone Derivatives from the Sponge-Associated Fungus Hypocrea Koningii PF04

Two new furan derivatives, hypofurans A and B (1 and 2), and three new cyclopentenone derivatives, hypocrenones A-C (3-5), along with seven known compounds (6-12), were isolated from a marine fungus Hypocrea koningii PF04 associated with the sponge Phakellia fusca. Among them, compounds 10 and 11 were obtained for the first time as natural products. The planar structures of compounds 1-5 were elucidated by analysis of their spectroscopic data. Meanwhile, the absolute configuration of 1 was determined as 2R,3R by the comparison of the experimental and calculated electronic circular dichroism (ECD) spectra. All the isolates were evaluated for their antibacterial and antioxidant activity. Compounds 1, 10, and 12 all showed modest antibacterial activity against Staphylococcus aureus ATCC25923 (MIC, 32 μg/mL). In addition, compounds 1, 10 and 11 exhibited moderate DPPH radical scavenging capacity with IC50 values of 27.4, 16.8, and 61.7 µg/mL, respectively.

Extra and intracellular synthesis of nickel oxide nanoparticles mediated by dead fungal biomass

The use of dead biomass of the fungus Hypocrea lixii as a biological system is a new, effective and environmentally friendly bioprocess for the production and uptake of nickel oxide nanoparticles (NPs), which has become a promising field in nanobiotechnology. Dead biomass of the fungus was successfully used to convert nickel ions into nickel oxide NPs in aqueous solution. These NPs accumulated intracellularly and extracellularly on the cell wall surface through biosorption. The average size, morphology and location of the NPs were characterized by transmission electron microscopy, high-resolution transmission electron microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The NPs were mainly spherical and extra and intracellular NPs had an average size of 3.8 nm and 1.25 nm, respectively. X-ray photoelectron spectroscopy analysis confirmed the formation of nickel oxide NPs. Infrared spectroscopy detected the presence of functional amide groups, which are probable involved in particle binding to the biomass. The production of the NPs by dead biomass was analyzed by determining physicochemical parameters and equilibrium concentrations. The present study opens new perspectives for the biosynthesis of nanomaterials, which could become a potential biosorbent for the removal of toxic metals from polluted sites.

Biocatalytic and antimicrobial activities of gold nanoparticles synthesized by Trichoderma sp

The aim of this work was to synthesize gold nanoparticles by Trichoderma viride and Hypocrea lixii. The biosynthesis of the nanoparticles was very rapid and took 10 min at 30 °C when cell-free extract of the T. viride was used, which was similar by H. lixii but at 100 °C. Biomolecules present in cell free extracts of both fungi were capable to synthesize and stabilize the formed particles. Synthesis procedure was very quick and environment friendly which did not require subsequent processing. The biosynthesized nanoparticles served as an efficient biocatalyst which reduced 4-nitrophenol to 4-aminophenol in the presence of NaBH₄ and had antimicrobial activity against pathogenic bacteria. To the best of our knowledge, this is the first report of such rapid biosynthesis of gold nanoparticles within 10 min by Trichoderma having plant growth promoting and plant pathogen control abilities, which served both, as an efficient biocatalyst, and a potent antimicrobial agent.

Biosynthesis and uptake of copper nanoparticles by dead biomass of Hypocrea lixii isolated from the metal mine in the Brazilian Amazon Region

A biological system for the biosynthesis of nanoparticles (NPs) and uptake of copper from wastewater, using dead biomass of Hypocrea lixii was analyzed and described for the first time. The equilibrium and kinetics investigation of the biosorption of copper onto dead, dried and live biomass of fungus were performed as a function of initial metal concentration, pH, temperature, agitation and inoculum volume. The high biosorption capacity was observed for dead biomass, completed within 60 min of contact, at pH 5.0, temperature of 40°C and agitation speed of 150 rpm with a maximum copper biosorption of 19.0 mg g⁻¹. The equilibrium data were better described using the Langmuir isotherm and kinetic analysis indicated that copper biosorption follows a pseudo-second-order model. The average size, morphology and location of NPs biosynthesized by the fungus were determined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). NPs were mainly spherical, with an average size of 24.5 nm, and were synthesized extracellularly. The X-ray diffraction (XRD) analysis confirms the presence of metallic copper particles. Infrared spectroscopy (FTIR) study revealed that the amide groups interact with the particles, which was accountable for the stability of NPs. This method further confirmed the presence of proteins as stabilizing and capping agents surrounding the copper NPs. These studies demonstrate that dead biomass of Hypocrea lixii provides an economic and technically feasible option for bioremediation of wastewater and is a potential candidate for industrial-scale production of copper NPs.

Enzymatic hydrolysis, adsorption, and recycling during hydrolysis of bagasse sulfite pulp

The high costs of enzymatic hydrolysis along with the high enzyme dosage are often considered as the major bottlenecks in lignocellulosic bioconversion. This study investigated the hydrolysis efficiency, cellulase adsorption and enzyme recycling during the hydrolysis of bagasse sulfite pulp (BSP). After 48 h of hydrolysis, more than 70% of the cellulose was hydrolyzed, while the protein concentration and cellulase activity in solution remained 31% and 17% of the initial value, respectively. The cellulase adsorption on the fresh BSP was better fitted by a Sips model, suggesting the occurrence of a multilayer adsorption at low cellulase concentration and monolayer adsorption at high concentration on the BSP surfaces. Desorption profile studies showed that the optimum desorption condition was at pH 4.8 and 40 °C. Moreover, considering the limited ability to desorption, directly empolying the bound enzyme with residual substrate is more effective method to recover cellulase during the hydrolysis of BSP.

Hypopulvins, novel peptaibiotics from the polyporicolous fungus Hypocrea pulvinata, are produced during infection of its natural hosts

In order to investigate the significance of antibiotics for the producing organism(s) in the natural habitat, we screened specimens of the polyporicolous fungus Hypocrea pulvinata growing on its natural hosts Piptoporus betulinus and Fomitopsis pinicola. Results showed that a particular group of nonribosomally biosynthesised antibiotic polypeptides, the peptaibiotics, which contain the nonproteinogenic marker amino acid α-aminoisobutyric acid (Aib), was produced in the natural habitat by the fungicolous producer and, consequently, released into the host. Using liquid chromatography coupled to electrospray high-resolution mass spectrometry we detected especially 19-, but also 11-, 18-, and 20-residue peptaibiotics in the five infected specimens analysed. Structures of peptaibiotics found were confirmed by analysing the peptaibiome of pure agar cultures obtained by single-ascospore isolation from the specimens. The 19-residue peptaibols were determined as deletion sequences of the trichosporins B lacking the Aib residue in position 6. Notably, 26 of the 28 peptaibiotics sequenced were novel; therefore the name 'hypopulvins' was introduced. Considering not only the ubiquity of both the two host species but also the highly specific association between H. pulvinata and P. betulinus/F. pinicola, and the abundance of this fungicolous species in north temperate regions of the world, a decisive role for the peptaibiotics detected in this study is predicted, which may act as mediators of the complex interactions between the basidiomycetous host and its fungicolous ascomycete 'partner'. Structural analogies of the hypopulvins, particularly with other 18-, 19-, and 20-residue peptaibiotics, suggest that the hypopulvins are forming transmembrane ion channels and could thus support the hypothesis of a parasitic lifestyle of the fungicolous producer.

Blue light acts as a double-edged sword in regulating sexual development of Hypocrea jecorina (Trichoderma reesei)

The industrially important cellulolytic filamentous fungus Trichoderma reesei is the anamorph of the pantropical ascomycete Hypocrea jecorina. H. jecorina CBS999.97 strain undergoes a heterothallic reproductive cycle, and the mating yields fertilized perithecia imbedded in stromata. Asci in the perithecia contain 16 linearly arranged ascospores. Here, we investigated H. jecorina sexual development under different light regimes, and found that visible light was dispensable for sexual development (stroma formation and ascospore discharge). By contrast, constant illumination inhibited stroma formation, and an interruption of the darkness facilitated timely stroma formation in a 12 h/12 h light-dark photoperiod. The results of genetic analyses further revealed that H. jecorina blue-light photoreceptors (BLR1, BLR2) and the photoadaptation protein ENV1 were not essential for sexual development in general. BLR1, BLR2 and ENV1 are orthologues of the conserved Neurospora crassa WC-1, WC-2 and VVD, respectively. Moreover, BLR1 and BLR2 mediate both positive and negative light-dependent regulation on sexual development, whereas ENV1 is required for dampening the light-dependent inhibitory effect in response to changes in illumination. Comparative genome-wide microarray analysis demonstrated an overview of light-dependent gene expression versus sexual potency in CBS999.97 (MAT1-2) haploid cells. Constant illumination promotes abundant asexual conidiation and high levels of hpp1 transcripts. hpp1 encodes a h (hybrid)-type propheromone that exhibits features of both yeast a and a pheromone precursors. Deletion of hpp1 could rescue stroma formation but not ascospore generation under constant illumination. We inferred that the HPP1-dependent pheromone signaling system might directly prevent stroma formation or simply disallow the haploid cells to acquire sexual potency due to abundant asexual conidiation upon constant illumination.

Metal-resistant microorganisms and metal chelators synergistically enhance the phytoremediation efficiency of Solanum nigrum L. in Cd- and Pb-contaminated soil

The effects of metal-resistant microorganisms and metal chelators on the ability of Solanum nigrum L. to accumulate heavy metals were investigated. In the presence of multiple metal contaminants (Cd and Pb), citric acid (CA) significantly enhanced the biomass and Cd accumulation of S. nigrum, but these conditions decreased the accumulation of Pb. Application of Cd- or Pb-resistant microorganisms improved the ability of S. nigrum to accumulate heavy metals and increased plant yield, but the effects of microorganisms on phytoextraction were smaller than the effects of CA. When plants were grown in the presence of Cd contamination, the co-application of CA and metal-resistant strains enhanced biomass by 30-50% and increased Cd accumulation by 25-35%. However, these conditions decreased Pb accumulation in the presence of Pb pollution. S. nigrum could tolerate a combination of Cd and Pb pollution. In the presence of CA and the metal-resistant microorganisms, the plants were able to acquire 15-25% more Cd and 10-15% more Pb than control plants. We propose that the synergistic combination of plants, microorganisms and chelators can enhance phytoremediation efficiency in the presence of multiple metal contaminants.

Molecular regulation of arabinan and L-arabinose metabolism in Hypocrea jecorina (Trichoderma reesei)

Hypocrea jecorina (anamorph: Trichoderma reesei) can grow on plant arabinans by the aid of secreted arabinan-degrading enzymes. This growth on arabinan and its degradation product L-arabinose requires the operation of the aldose reductase XYL1 and the L-arabinitol dehydrogenase LAD1. Growth on arabinan and L-arabinose is also severely affected in a strain deficient in the general cellulase and hemicellulase regulator XYR1, but this impairment can be overcome by constitutive expression of the xyl1 encoding the aldose reductase. An inspection of the genome of H. jecorina reveals four genes capable of degrading arabinan, i.e., the alpha-L-arabinofuranosidase encoding genes abf1, abf2, and abf3 and also bxl1, which encodes a beta-xylosidase with a separate alpha-L-arabinofuranosidase domain and activity but no endo-arabinanase. Transcriptional analysis reveals that in the parent strain QM9414 the expression of all of these genes is induced by L-arabinose and to a lesser extent by L-arabinitol and absent on D-glucose. Induction by L-arabinitol, however, is strongly enhanced in a Deltalad1 strain lacking L-arabinitol dehydrogenase activity and severely impaired in an aldose reductase (Deltaxyl1) strain, suggesting a cross talk between L-arabinitol and the aldose reductase XYL1 in an alpha-L-arabinofuranosidase gene expression. Strains bearing a knockout in the cellulase regulator xyr1 do not show any induction of abf2 and bxl1, and this phenotype cannot be reverted by constitutive expression of xyl1. The loss of function of xyr1 has also a slight effect on the expression of abf1 and abf3. We conclude that the expression of the four alpha-L-arabinofuranosidases of H. jecorina for growth on arabinan requires an early pathway intermediate (L-arabinitol or L-arabinose), the first enzyme of the pathway XYL1, and in the case of abf2 and bxl1 also the function of the cellulase regulator XYR1.

Microbial transformation of a monoterpene, geraniol, by the marine-derived fungus Hypocrea sp

Geraniol (1) is the biogenetic precursor of a number of monoterpenes. We tested various marine-derived microorganisms to determine their ability to biotransform 1. Only Hypocrea sp. was capable of transforming 1 into its oxidized derivative, 1,7-dihydroxy-3,7-dimethyl-(E)-oct- 2-ene (2). The structure of the metabolite obtained was assigned on the basis of detailed spectroscopic data analyses.

Lack of aldose 1-epimerase in Hypocrea jecorina (anamorph Trichoderma reesei): a key to cellulase gene expression on lactose

The heterodisaccharide lactose (1,4-O-beta-D-galactopyranosyl-D-glucose) induces cellulase formation in the ascomycete Hypocrea jecorina (= Trichoderma reesei). Lactose assimilation is slow, and the assimilation of its beta-D-galactose moiety depends mainly on the operation of a recently described reductive pathway and depends less on the Leloir pathway, which accepts only alpha-D-galactose. We therefore reasoned whether galactomutarotase [aldose 1-epimerase (AEP)] activity might limit lactose assimilation and thus influence cellulase formation. We identified three putative AEP-encoding genes (aep1, aep2, aep3) in H. jecorina, of which two encoded intracellular protein (AEP1 and AEP2) and one encoded an extracellular protein (AEP3). Although all three were transcribed, only the aep3 transcript was detected on lactose. However, no mutarotase activity was detected in the mycelia, their cell walls, or the extracellular medium during growth on lactose. Therefore, the effect of galactomutarotase activity on lactose assimilation was studied with H. jecorina strains expressing the C-terminal galactose mutarotase part of the Saccharomyces cerevisiae Gal10. These strains showed increased growth on lactose in a gene copy number-dependent manner, although their formation of extracellular beta-galactosidase activity and transcription of the genes encoding the first steps in the Leloir and the reductive pathway was similar to the parental strain QM9414. Cellulase gene transcription on lactose dramatically decreased in these strains, but remained unaffected during growth on cellulose. Our data show that cellulase induction in H. jecorina by lactose requires the beta-anomer of D-galactose and reveal the lack of mutarotase activity during growth on lactose as an important key for cellulase formation on this sugar.

Xyr1 receives the lactose induction signal and regulates lactose metabolism in Hypocrea jecorina

This study reports the vital regulatory influence of Xyr1 (xylanase regulator 1) on the transcription of hydrolytic enzyme-encoding genes and hydrolase formation on lactose in Hypocrea jecorina. While the transcription of the xyr1 gene itself is achieved by release of carbon catabolite repression, the transcript formation of xyn1 (xylanase 1) is regulated by an additional induction mechanism mediated by lactose. Xyr1 has an important impact on lactose metabolism by directly activating xyl1 (xylose reductase 1) transcription and indirectly influencing transcription of bga1 (beta-galactosidase 1). The latter is achieved by regulating the conversion of D-galactose to the inducing carbon source galactitol.

Harzianums A and B produced by a fungal strain, Hypocrea sp. F000527, and their cytotoxicity against tumor cell lines

A new compound, harzianum B (1), was isolated from the culture broth of a fungal strain, Hypocrea sp. F000527, together with a known trichothecene, harzianum A (2). Its structure was determined by spectroscopic analyses including HRFAB-MS and various (1)H NMR and (13)C NMR spectral data. Harzianum B (1) was characterised as (E,Z,E)-2', 4', 6'-octatriendioic acid esterified on the 4beta-hydroxyl group of trichodermol. Harzianums A (2) and B (1) showed cytotoxicity against several human cancer cell lines.

An investigation of the substrate specificity of the xyloglucanase Cel74A from Hypocrea jecorina

The substrate specificity of the xyloglucanase Cel74A from Hypocrea jecorina (Trichoderma reesei) was examined using several polysaccharides and oligosaccharides. Our results revealed that xyloglucan chains are hydrolyzed at substituted Glc residues, in contrast to the action of all known xyloglucan endoglucanases (EC 3.2.1.151). The building block of xyloglucan, XXXG (where X is a substituted Glc residue, and G is an unsubstituted Glc residue), was rapidly degraded to XX and XG (k(cat) = 7.2 s(-1) and Km = 120 microM at 37 degrees C and pH 5), which has only been observed before with the oligoxyloglucan-reducing-end-specific cellobiohydrolase from Geotrichum (EC 3.2.1.150). However, the cellobiohydrolase can only release XG from XXXGXXXG, whereas Cel74A hydrolyzed this substrate at both chain ends, resulting in XGXX. Differences in the length of a specific loop at subsite + 2 are discussed as being the basis for the divergent specificity of these xyloglucanases.

Induction of extracellular β-galactosidase (Bga1) formation by d-galactose in Hypocrea jecorina is mediated by galactitol

The ability of Hypocrea jecorina (Trichoderma reesei) to grow on lactose strongly depends on the formation of an extracellular glycoside hydrolase (GH) family 35 beta-galactosidase, encoded by the bga1 gene. Previous studies, using batch or transfer cultures of pregrown cells, had shown that bga1 is induced by lactose and d-galactose, but to a lesser extent by galactitol. To test whether the induction level is influenced by the different growth rates attainable on these carbon sources, bga1 expression was compared in carbon-limited chemostat cultivations at defined dilution (=specific growth) rates. The data showed that bga1 expression by lactose, d-galactose and galactitol positively correlated with the dilution rate, and that galactitol and d-galactose induced the highest activities of beta-galactosidase at comparable growth rates. To know more about the actual inducer for beta-galactosidase formation, its expression in H. jecorina strains impaired in the first steps of the two d-galactose-degrading pathways was compared. Induction by d-galactose and galactitol was still found in strains deleted in the galactokinase-encoding gene gal1, which is responsible for the first step of the Leloir pathway of d-galactose catabolism. However, in a strain deleted in the aldose/d-xylose reductase gene xyl1, which performs the reduction of d-galactose to galactitol in a recently identified second pathway, induction by d-galactose, but not by galactitol, was impaired. On the other hand, induction by d-galactose and galactitol was not affected in an l-arabinitol 4-dehydrogenase (lad1)-deleted strain which is impaired in the subsequent step of galactitol degradation. These results indicate that galactitol is the actual inducer of Bga1 formation during growth on d-galactose in H. jecorina.

Direct identification of hydrophobins and their processing in Trichoderma using intact-cell MALDI-TOF MS

Intact-cell MS (ICMS) was applied for the direct detection of hydrophobins in various species and strains of Hypocrea/Trichoderma. In both mycelia and spores, dominating peaks were identified as hydrophobins by detecting mass shifts of 8 Da of reduced and unreduced forms, the analysis of knockout mutants, and comparison with protein databases. Strain-specific processing was observed in the case of Hypocrea jecorina (anamorph Trichoderma reesei). An analysis of 32 strains comprising 29 different species of Trichoderma and Hypocrea showed hydrophobin patterns that were specific at both at the species and isolate (subspecies) levels. The method therefore permits rapid and direct detection of hydrophobin class II compositions and may also provide a means to identify Trichoderma (and other fungal) species and strains from microgram amounts of biomass without prior cultivation.

Epl1, the major secreted protein of Hypocrea atroviridis on glucose, is a member of a strongly conserved protein family comprising plant defense response elicitors

We used a proteomic approach to identify constitutively formed extracellular proteins of Hypocrea atroviridis (Trichoderma atroviride), a known biocontrol agent. The fungus was cultivated on glucose and the secretome was examined by two-dimensional gel electrophoresis. The two predominant spots were identified by MALDI MS utilizing peptide mass fingerprints and amino acid sequence tags obtained by postsource decay and/or high-energy collision-induced dissociation (MS/MS) experiments, and turned out to be the same protein (12 629 Da as determined with MS, pI 5.5-5.7), probably representing the monomer and the dimer. The corresponding gene was subsequently cloned from H. atroviridis and named epl1 (eliciting plant response-like), because it encodes a protein that exhibits high similarity to the cerato-platanin family, which comprises proteins such as cerato-platanin from Ceratocystis fimbriata f. sp. platani and Snodprot1 of Phaeosphaeria nodorum, which have been reported to be involved in plant pathogenesis and elicitation of plant defense responses. Additionally, based on the similarity of the N-terminus to that of H. atroviridis Epl1, we conclude that a previously identified 18 kDa plant response elicitor isolated from T. virens is an ortholog of epl1. Our results showed that epl1 transcript was present under all growth conditions tested, which included the carbon sources glucose, glycerol, l-arabinose, d-xylose, colloidal chitin and cell walls of the plant pathogen Rhizoctonia solani, and also plate confrontation assays with R. solani. Epl1 transcript could even be detected under osmotic stress, and carbon and nitrogen starvation.

Xyr1 (xylanase regulator 1) regulates both the hydrolytic enzyme system and D-xylose metabolism in Hypocrea jecorina

Xyr1 (xylanase regulator 1) of the ascomycete Hypocrea jecorina (anamorph Trichoderma reesei) was recently demonstrated to play an essential role in the transcriptional regulation of the xyn1 (xylanase 1-encoding) gene expression. Consequently, this study reports on the deletion of the xyr1 gene from the H. jecorina genome. Comparative studies of the growth behavior of the different mutant strains (deleted and retransformed xyr1) grown on various carbon sources pointed to the strongly reduced ability of the xyr1 deletion strain to utilize D-xylose and xylan. Transcriptional analysis of the xyl1 (D-xylose reductase 1-encoding) gene as well as measurements of corresponding enzymatic activities gave evidence that Xyr1 takes part in the control of the fungal D-xylose pathway, in particular in the regulation of D-xylose reductase. It could be demonstrated that the uptake of D-xylose into the fungal cell is uninfluenced in the Deltaxyr1 strain. Furthermore, transcriptional regulation of the major hydrolytic enzyme-encoding genes xyn1 and xyn2 (xylanases 1 and 2), cbh1 and cbh2 (cellobiohydrolases 1 and 2), and egl1 (endoglucanase 1) is strictly dependent on Xyr1. Regulation of the respective genes via Xyr1 is not affected by the substances mediating induction (xylose, xylobiose, and sophorose) and is indispensable for all modes of gene expression (basal, derepressed, and induced). Moreover, Xyr1, it was revealed, activated transcriptional regulation of inducer-providing enzymes such as beta-xylosidase BXLI and beta-glucosidase BGLI but was not shown to be involved in the regulation of BGLII.

L-galactonate dehydratase is part of the fungal path for D-galacturonic acid catabolism

An L-galactonate dehydratase and the corresponding gene were identified from the mould Hypocrea jecorina (Trichoderma reesei). This novel enzyme converts L-galactonate to L-threo-3-deoxy-hexulosonate (2-keto-3-deoxy-L-galactonate). The enzyme is part of the fungal pathway for D-galacturonic acid catabolism, a pathway which is only partly known. It is the second enzyme of this pathway after the D-galacturonic acid reductase. L-galactonate dehydratase activity is present in H. jecorina cells grown on D-galacturonic acid but absent when other carbon sources are used for growth. A deletion of the L-galactonate dehydratase gene in H. jecorina results in a strain with no growth on D-galacturonic acid. The active enzyme was produced in the heterologous host Saccharomyces cerevisiae and characterized. It exhibited activity with L-galactonate and D-arabonate where the hydroxyl group of the C2 is in L- and the hydroxyl group of the C3 is in D-configuration in the Fischer projection. However, it did not exhibit activity with D-galactonate, D-gluconate, L-gulonate or D-xylonate where the hydroxyl groups of the C2 and C3 are in different configuration.

Global carbon utilization profiles of wild-type, mutant, and transformant strains of Hypocrea jecorina

The ascomycete Hypocrea jecorina (Trichoderma reesei), an industrial producer of cellulases and hemicellulases, can efficiently degrade plant polysaccharides. However, the catabolic pathways for the resulting monomers and their relationship to enzyme induction are not well known. Here we used the Biolog Phenotype MicroArrays technique to evaluate the growth of H. jecorina on 95 carbon sources. For this purpose, we compared several wild-type isolates, mutants producing different amounts of cellulases, and strains transformed with a heterologous antibiotic resistance marker gene. The wild-type isolates and transformed strains had the highest variation in growth patterns on individual carbon sources. The cellulase mutants were relatively similar to their parental strains. Both in the mutant and in the transformed strains, the most significant changes occurred in utilization of xylitol, erythritol, D-sorbitol, D-ribose, D-galactose, L-arabinose, N-acetyl-D-glucosamine, maltotriose, and beta-methyl-glucoside. Increased production of cellulases was negatively correlated with the ability to grow on gamma-aminobutyrate, adonitol, and 2-ketogluconate; and positively correlated with that on d-sorbitol and saccharic acid. The reproducibility, relative simplicity, and high resolution (+/-10% of increase in mycelial density) of the phenotypic microarrays make them a useful tool for the characterization of mutant and transformed strains and for a global analysis of gene function.

d-Galactose induces cellulase gene expression in Hypocrea jecorina at low growth rates

Lactose (1,4-O-β-d-galactopyranosyl-d-glucose) is a soluble and economic carbon source for the industrial production of cellulases or recombinant proteins by Hypocrea jecorina (anamorph Trichoderma reesei). The mechanism by which lactose induces cellulase formation is not understood. Recent data showed that the galactokinase step is essential for cellulase induction by lactose, but growth on d-galactose alone does not induce cellulases. Consequently, the hypothesis was tested that d-galactose may be an inducer only at a low growth rate, which is typically observed when growing on lactose. Carbon-limited chemostat cultivations of H. jecorina were therefore performed at different dilution rates with d-galactose, lactose, galactitol and d-glucose. Cellulase gene expression was monitored by using a strain carrying a fusion between the cbh2 (encoding cellobiohydrolase 2, Cel6A) promoter region and the Aspergillus niger glucose oxidase gene and by identification of the two major cellobiohydrolases Cel7A and Cel6A. The results show that d-galactose indeed induces cbh2 gene transcription and leads to Cel7A and Cel6A accumulation at a low (D=0·015 h−1) but not at higher dilution rates. At the same dilution rate, growth on d-glucose did not lead to cbh2 promoter activation or Cel6A formation but a basal level, lower than that observed on d-galactose, was detected for the carbon-catabolite-derepressible Cel7A. Lactose induced significantly higher cellulase levels at 0·015 h−1 than d-galactose and induced cellulases even at growth rates up to 0·042 h−1. Results of chemostats with an equimolar mixture of d-galactose and d-glucose essentially mimicked the behaviour on d-galactose alone, whereas an equimolar mixture of d-galactose and galactitol, the first intermediate of a recently described second pathway of d-galactose catabolism, led to cellulase induction at D=0·030 h−1. It is concluded that d-galactose indeed induces cellulases at low growth rate and that the operation of the alternative pathway further increases this induction. However, under those conditions lactose is still a superior inducer for which the mechanism remains to be clarified.

A new Hypocrea strain producing harzianum A cytotoxic to tumour cell lines

AIMS

To identify a new fungal strain, Hypocrea sp. F000527 producing a trichothecene metabolite, harzianum A, and to evaluate its cytotoxicity to tumour cell lines.

METHODS AND RESULTS

A fungal strain, F000527, with cytotoxic activity was identified as a new Hypocrea strain based on morphological characteristics and internal transcribed spacers rDNA sequence data. Harzianum A was isolated from wheat bran culture by 50% acetone extraction, silica gel chromatography, Sephadex LH-20 chromatography and HPLC. The chemical structures were determined by ESI- or HRFAB-MS and (1)H and (13)C-NMR analyses. Harzianum A showed cytotoxicity to HT1080 and HeLa cell lines with IC(50) value of 0.65 and 5.07 Łg ml(-1) respectively.

CONCLUSIONS

Harzianum A with a chemical formula of C(23)H(28)O(6) was isolated from a new Hypocrea strain and showed moderate to strong cytotoxicity to human cancer cell lines.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of the production of cytotoxic harzianum A by a new Hypocrea strain.

The galactokinase of Hypocrea jecorina is essential for cellulase induction by lactose but dispensable for growth on d-galactose

Lactose is the only soluble carbon source which can be used economically for the production of cellulases or heterologous proteins under cellulase expression signals by Hypocrea jecorina (=Trichoderma reesei). Towards an understanding of lactose metabolism and its role in cellulase formation, we have cloned and characterized the gal1 (galactokinase) gene of H. jecorina, which catalyses the first step in d-galactose catabolism. It exhibits a calculated Mr of 57 kDa, and shows moderate identity (about 40%) to its putative homologues of Saccharomyces cerevisiae and Kluyveromyces lactis. Gal1 is a member of the GHMP family, shows conservation of a Gly/Ser rich region involved in ATP binding and of amino acids (Arg 51, Glu 57, Asp 60, Asp 214, Tyr 270) responsible for galactose binding. A single transcript was formed constitutively during the rapid growth phase on all carbon sources investigated and accumulated to about twice this level during growth on d-galactose, l-arabinose and their corresponding polyols. Deletion of gal1 reduces growth on d-galactose but does only slightly affect growth on lactose. This is the result of the operation of a second pathway for d-galactose catabolism, which involves galactitol as an intermediate, and whose transient concentration is strongly enhanced in the delta-gal1 strain. In this pathway, galactitol is catabolised by the lad1-encoded l-arabinitol-4-dehydrogenase, because a gal1/lad1 double delta-mutant failed to grow on d-galactose. In the delta-gal1 strain, induction of the Leloir pathway gene gal7 (encoding galactose-1-phosphate uridylyltransferase) by d-galactose, but not by l-arabinose, is impaired. Induction of cellulase gene expression by lactose is also impaired in a gal1 deleted strain, whereas their induction by sophorose (the putative cellulose-derived inducer) was shown to be normal, thus demonstrating that galactokinase is a key enzyme for cellulase induction during growth on lactose, and that induction by lactose and sophorose involves different mechanisms.

Heterogeneity of homologously expressed Hypocrea jecorina (Trichoderma reesei) Cel7B catalytic module

The catalytic module of Hypocrea jecorina (previously Trichoderma reesei) Cel7B was homologously expressed by transformation of strain QM9414. Post-translational modifications in purified Cel7B preparations were analysed by enzymatic digestions, high performance chromatography, mass spectrometry and site-directed mutagenesis. Of the five potential sites found in the wild-type enzyme, only Asn56 and Asn182 were found to be N-glycosylated. GlcNAc(2)Man(5) was identified as the predominant N-glycan, although lesser amounts of GlcNAc(2)Man(7) and glycans carrying a mannophosphodiester bond were also detected. Repartition of neutral and charged glycan structures over the two glycosylation sites mainly accounts for the observed microheterogeneity of the protein. However, partial deamidation of Asn259 and a partially occupied O-glycosylation site give rise to further complexity in enzyme preparations.

D-xylose metabolism in Hypocrea jecorina: loss of the xylitol dehydrogenase step can be partially compensated for by lad1-encoded L-arabinitol-4-dehydrogenase

With the goal of the genetic characterization of the D-xylose pathway in Hypocrea jecorina (anamorph: Trichoderma reesei), we cloned the xdh1 gene, encoding NAD-xylitol dehydrogenase, which catalyzes the second step of fungal D-xylose catabolism. This gene encodes a 363-amino-acid protein which has a mass of 38 kDa, belongs to the zinc-containing alcohol dehydrogenase family, exhibits high sequence identity to the published sequences of xylitol dehydrogenases from yeast origins, but contains a second, additional binding site for Zn2+. The enzyme catalyzed the NAD-dependent oxidation of xylitol and D-sorbitol and the NADH-dependent reduction of D-xylulose and D-fructose. No activity was observed with NADP, L-arabinose, or L-arabinitol. A single 1.4-kb transcript was formed during growth on xylan, D-xylose, L-arabinose, L-arabinitol and, at a lower abundance, xylitol, D-galactose, galactitol, and lactose but not on D-glucose and glycerol. xdh1 deletion mutants exhibited 50% reduced growth rates on D-xylose, whereas growth rates on xylitol remained unaltered. These mutants contained 30% of the xylitol dehydrogenase activity of the parent strain, indicating the presence of a second xylitol dehydrogenase. This activity was shown to be due to lad1-encoded L-arabinitol-4-dehydrogenase, because H. jecorina xdh1 lad1 double-deletion strains failed to grow on D-xylose or xylitol. In contrast, lad1 deletion strains of H. jecorina grew normally on these carbon sources. These results show that H. jecorina contains a single xylitol dehydrogenase which is encoded by xdh1 and is involved in the metabolism of D-xylose and that lad1-encoded L-arabinitol-4-dehydrogenase can compensate for it partially in mutants with a loss of xdh1 function.