Production Of Fungal Metabolites Research Articles

The investigation of epigenetic modifiers in cultures of an endophytic fungus to enhance PPT production

Podophyllotoxin (PPT) is a natural plant lignan used for the semi-synthesis of anti-cancer drugs. Due to a variety of factors, PPT is becoming less available. An endophytic fungus, PPE7, from Podophyllum peltatum, can serve as an alternate source of PPT, but production declined over several generations of subculture, perhaps due to gene silencing. Small molecule epigenetic modifiers, such as DNA methyl transferase (DNMT) and histone deacytelase (HDAC) inhibitors, can activate silent fungal pathways and enhance the production of fungal metabolites. Re-activation of the PPT pathway may make it possible to identify the genes involved in PPT synthesis through cDNA analysis. The HDAC inhibitor, suberoylanilide hydroxamic acid (SAHA) and the DNMT inhibitor 5-azacytidine (5-aza) were used to treat cultures of PPE7. Extracts were prepared by solid phase extraction (SPE) and analyzed by HPLC. Cultures treated with SAHA and 5-aza showed gain of peaks, loss of peaks and altered amounts of individual peaks compared to the untreated cultures. Thus, both epigenetic modifiers are capable of affecting the compounds produced in cultures of PPE7. LC-MS analysis is in progress to further confirm these findings and explore the production of PPT and related lignans in the treated cultures.

A Practical Strategy to Discover New Antitumor Compounds by Activating Silent Metabolite Production in Fungi by Diethyl Sulphate Mutagenesis

Many fungal biosynthetic pathways are silent in standard culture conditions, and activation of the silent pathways may enable access to new metabolites with antitumor activities. The aim of the present study was to develop a practical strategy for microbial chemists to access silent metabolites in fungi. We demonstrated this strategy using a marine-derived fungus Penicillium purpurogenum G59 and a modified diethyl sulphate mutagenesis procedure. Using this strategy, we discovered four new antitumor compounds named penicimutanolone (1), penicimutanin A (2), penicimutanin B (3), and penicimutatin (4). Structures of the new compounds were elucidated by spectroscopic methods, especially extensive 2D NMR analysis. Antitumor activities were assayed by the MTT method using human cancer cell lines. Bioassays and HPLC-photodiode array detector (PDAD)-UV and HPLC-electron spray ionization (ESI)-MS analyses were used to estimate the activated secondary metabolite production. Compounds 2 and 3 had novel structures, and 1 was a new compound belonging to a class of very rare natural products from which only four members are so far known. Compounds 1–3 inhibited several human cancer cell lines with IC50 values lower than 20 μM, and 4 inhibited the cell lines to some extent. These results demonstrated the effectiveness of this strategy to discover new compounds by activating silent fungal metabolic pathways. These discoveries provide rationale for the increased use of chemical mutagenesis strategies in silent fungal metabolite studies.

A Novel Approach to Enhancing Ganoderic Acid Production by Ganoderma lucidum Using Apoptosis Induction

Ganoderma lucidum is one of most widely used herbal medicine and functional food in Asia, and ganoderic acids (GAs) are its active ingredients. Regulation of GA biosynthesis and enhancing GA production are critical to using G. lucidum as a medicine. However, regulation of GA biosynthesis by various signaling remains poorly understood. This study investigated the role of apoptosis signaling on GA biosynthesis and presented a novel approach, namely apoptosis induction, to increasing GA production. Aspirin was able to induce cell apoptosis in G. lucidum, which was identified by terminal deoxynucleotidyl transferase mediated dUPT nick end labeling assay positive staining and a condensed nuclear morphology. The maximum induction of lanosta-7,9(11), 24-trien-3α-01-26-oic acid (ganoderic acid 24, GA24) production and total GA production by aspirin were 2.7-fold and 2.8-fold, respectively, after 1 day. Significantly lower levels of GA 24 and total GAs were obtained after regular fungal culture for 1.5 months. ROS accumulation and phosphorylation of Hog-1 kinase, a putative homolog of MAPK p38 in mammals, occurred after aspirin treatment indicating that both factors may be involved in GA biosynthetic regulation. However, aspirin also reduced expression of the squalene synthase and lanosterol synthase coding genes, suggesting that these genes are not critical for GA induction. To the best of our knowledge, this is the first report showing that GA biosynthesis is linked to fungal apoptosis and provides a new approach to enhancing secondary metabolite production in fungi.

Order in the playground

In eukaryotes the arrangement of genes along the chromosome is not as random as it at first appeared, and distinctive clusters of functionally related but non-homologous genes can be found in the genomes of certain animals and fungi. These include the major histocompatibility complex in mammals and gene clusters for nutrient use and secondary metabolite production in fungi. A growing number of functional gene clusters for different types of secondary metabolite are now being discovered in plant genomes. However, the molecular mechanisms and evolutionary pressures behind their formation are poorly understood. Here we discuss the implications of our recent investigation into the origin of two functional gene clusters in the model plant Arabidopsis thaliana.

Antifungal Effects on Metabolite Profiles of Medically Important Yeast Species Measured by Nuclear Magnetic Resonance Spectroscopy

Drug-induced inhibition of fungal growth is used in the diagnostic laboratory to predict therapeutic efficacy but is relatively slow, and determination of endpoints can be problematic. Nuclear magnetic resonance (NMR) spectroscopy identifies the metabolic complement of microorganisms while monitoring utilization of constituents of the incubation medium. This technique may provide a rapid and objective indicator of antifungal effects. We evaluated the effects of caspofungin, amphotericin B (AMB), and voriconazole on metabolic profiles of yeast species cultured in RPMI-2% glucose-morpholinepropanesulfonic acid buffer in microtiter plates in a proof-of-principle study. 1H NMR spectra were obtained using Bruker NMR spectrometers at 1H frequencies of 600 and 360 MHz. Metabolites were identified by two-dimensional correlation NMR spectra, and relative peak integrals were calculated from one-dimensional 1H NMR spectra. MICs were determined by a modification of the Clinical and Laboratory Standards Institute broth microdilution method M27-A. Utilization of glucose and branched-chain and aromatic amino acid substrates was accompanied by fungal production of acetate, acetaldehyde, ethanol, formate, fumarate, glycerol, lactate, pyruvate, and succinate. Clear-cut metabolic endpoints indicating a greater than 50% reduction in substrate utilization and fungal metabolite production which correlated with MICs were noted at 16 and 24 h for all three drugs. At 8 h, reductions of greater than 50% for selected metabolites were noted for caspofungin and AMB. Direct NMR-based observation of metabolic alterations in yeast cultures reveals changes in key metabolic pathways and should be evaluated formally as a rapid technique for determining susceptibility to antifungal drugs.

Regulatory elements in aflatoxin biosynthesis

This review provides a synopsis of factors involved in the regulation of aflatoxin inAspergillus species at the molecular level. Much of the knowledge available today on the regulation of secondary metabolite production in fungi has been gleaned from studies of the aflatoxin gene cluster inA. flavus andA. parasiticus and the sterigmatocystin gene cluster inA. nidulans. Regulation of these two gene clusters is under the control of both pathway-specific transcription factors such as AflR and AflJ and global or broad-domain transcription factors such as AreA and PacC. Study of secondary metabolite (sec-) mutants inA. parasiticus first identified an association between mycotoxin production and fungal development. This linkage has been extended at the molecular level by the characterization of a G-protein/cAMP/Protein kinase A signaling pathway that regulates sporulation via the transcription factor BrlA and aflatoxin/sterigmatocystin production via AflR. Another global regulator of mycotoxin production, VeA, mediates a developmental light-response inA. nidulans andA. flavus. Though not similar to any known fungal transcriptional regulators, VeA controls aflatoxin/sterigmatocystin production via transcriptional control of AflR and it also regulates development of sexual structures such as cleistothecia inA. nidulans and sclerotia inA. flavus.

Micro-scale extraction procedure for standardized screening of fungal metabolite production in cultures

A simple and rapid standardized micro-scale extraction procedure has been developed to prepare extracts from fungal cultures for high-performance liquid chromatographic (HPLC) analysis. The method is based on ultrasonic extraction of three 6-mm plugs cut from a culture using 0.5 ml of solvent followed by a simple solvent change, filtration and injection. Approximately 5 min of work is involved in the extraction and work-up process and the extract can prepared for HPLC analysis within 60–70 min. The method has been used for determination of chromatographic metabolite profiles from 395 fungal isolates, including all terverticillate Penicillium species, cultivated on both Czapek Yeast Autolysate agar and Yeast Extract Sucrose agar. The concentration of the extracts proved to be sufficient to determine all secondary metabolites reported to be produced by these species using HPLC with diode array detection. These findings were confirmed by analyses of 132 pure metabolite standards.

In vivo development of the entomogeneous hyphomycetePaecilomyces farinosus in hostSpodoptera exigua (beet armyworm) larvae

The in vivo development of the entomogenous hyphomycetePaecilomyces farinosus inSpodoptera exigua (beet armyworm) larvae was examined using light and electron microscopic techniques. Blastospores injected into larval hemocoels (500 blastospores/larva) were immediately ingested by phagocytic hemocytes, and no fungal cells were detected in the hemolymph until ∼36 h post-injection. As indicated by immunocytochemical methods, the in vivo-produced blastosopres, in contrast to in vitro blastospores, lacked a galacto-mannan surface layer required for opsonization by aS. exigua humoral lectin. Therefore, these in vivo cells were not recognized by phagocytic granulocytes and were freely-circulating in the hemolymph. Hyphae differentiating from the blastospores were recognized by the hemocytes and induced formation of multicellular hemocytic nodules. By 72 h post-injection, mycelia were observed emerging from the nodules and by 96 h, larvae had become mummified due to extensive proliferation of the fungus throughout host tissues. Neither phagocytosis of the initially injected in vitro-produced blastospores nor nodule formation around hyphal cells later in the infection process was effective in stopping fungal growth. The in vivo development ofP. farinosus was similar to that of another hyphomycete,Beauveria bassiana except that in the latter case, extensive nodule formation was inhibited by the production of fungal metabolites.

Differentiation and secondary metabolism in some prokaryotes and fungi

Relationships between growth and differentiation and secondary metabolism in microorganisms are reviewed and discussed. The trophophase/idiophase concept is illustrated by patulin biosynthesis. Other features of the biosynthesis of secondary metabolites (such as β-lactams, mycophenolic acid, rubratoxin, enniatin, tentoxin and citrinin) are also presented. Examples of secondary metabolism in relation to differentiation of selected prokaryotes (bacteria and actinomycetes) are also given. The major part of the review concerns relationships of differentiation and secondary metabolite production in fungi. The following metabolites are discussed: cephalosporin C, brefeldin A, ergot alkaloids, solanopyrone phytotoxins, verruculogen, griseofulvin, penitrems, paxilline, patulin, anthraquinones, mycosporines, P-factor, cyclopenin, cyclopenol, zearalenone, and sex hormones of lower fungi (trisporic acid, antheridiol and sirenin).

Design of solid state fermentor for production of fungal metabolites on large scale

A large scale solid state fermentor of 150 tray capacity is designed with appropriate control system. It gave better productivity even at higher scale of operation as compared to lab and large scale units of similar type and largely overcomes some operational problems.