A New N-methoxypyridone from the Co-Cultivation of Hawaiian Endophytic Fungi Camporesia sambuci FT1061 and Epicoccum sorghinum FT1062

The Potential Use of Fungal Co-Culture Strategy for Discovery of New Secondary Metabolites

Fungi are an important and prolific source of secondary metabolites (SMs) with diverse chemical structures and a wide array of biological properties. In the past two decades, however, the number of new fungal SMs by traditional monoculture method had been greatly decreasing. Fortunately, a growing number of studies have shown that co-culture strategy is an effective approach to awakening silent SM biosynthetic gene clusters (BGCs) in fungal strains to produce cryptic SMs. To enrich our knowledge of this approach and better exploit fungal biosynthetic potential for new drug discovery, this review comprehensively summarizes all fungal co-culture methods and their derived new SMs as well as bioactivities on the basis of an extensive literature search and data analysis. Future perspective on fungal co-culture study, as well as its interaction mechanism, is supplied.

Fungal-fungal co-culture: a primer for generating chemical diversity

Covering: 2002 to 2020In their natural environment, fungi must compete for resources. It has been hypothesized that this competition likely induces the biosynthesis of secondary metabolites for defence. In a quest to discover new chemical diversity from fungal cultures, a growing trend has been to recapitulate this competitive environment in the laboratory, essentially growing fungi in co-culture. This review covers fungal-fungal co-culture studies beginning with the first literature report in 2002. Since then, there has been a growing number of new secondary metabolites reported as a result of fungal co-culture studies. Specifically, this review discusses and provides insights into (1) rationale for pairing fungal strains, (2) ways to grow fungi for co-culture, (3) different approaches to screening fungal co-cultures for chemical diversity, (4) determining the secondary metabolite-producing strain, and (5) final thoughts regarding the fungal-fungal co-culture approach. Our goal is to provide a set of practical strategies for fungal co-culture studies to generate unique chemical diversity that the natural products research community can utilize.

Oxic and Anoxic Organic Polymer Degradation Potential of Endophytic Fungi From the Marine Macroalga, Ecklonia radiata

Cellulose and chitin are the most abundant polymeric, organic carbon source globally. Thus, microbes degrading these polymers significantly influence global carbon cycling and greenhouse gas production. Fungi are recognized as important for cellulose decomposition in terrestrial environments, but are far less studied in marine environments, where bacterial organic matter degradation pathways tend to receive more attention. In this study, we investigated the potential of fungi to degrade kelp detritus, which is a major source of cellulose in marine systems. Given that kelp detritus can be transported considerable distances in the marine environment, we were specifically interested in the capability of endophytic fungi, which are transported with detritus, to ultimately contribute to kelp detritus degradation. We isolated 10 species and two strains of endophytic fungi from the kelp Ecklonia radiata. We then used a dye decolorization assay to assess their ability to degrade organic polymers (lignin, cellulose, and hemicellulose) under both oxic and anoxic conditions and compared their degradation ability with common terrestrial fungi. Under oxic conditions, there was evidence that Ascomycota isolates produced cellulose-degrading extracellular enzymes (associated with manganese peroxidase and sulfur-containing lignin peroxidase), while Mucoromycota isolates appeared to produce both lignin and cellulose-degrading extracellular enzymes, and all Basidiomycota isolates produced lignin-degrading enzymes (associated with laccase and lignin peroxidase). Under anoxic conditions, only three kelp endophytes degraded cellulose. We concluded that kelp fungal endophytes can contribute to cellulose degradation in both oxic and anoxic environments. Thus, endophytic kelp fungi may play a significant role in marine carbon cycling via polymeric organic matter degradation.

Fungal Endophytes: A Promising Frontier for Discovery of Novel Bioactive Compounds

For years, fungi have served as repositories of bioactive secondary metabolites that form the backbone of many existing drugs. With the global rise in infections associated with antimicrobial resistance, in addition to the growing burden of non-communicable disease, such as cancer, diabetes and cardiovascular ailments, the demand for new drugs that can provide an improved therapeutic outcome has become the utmost priority. The exploration of microbes from understudied and specialized niches is one of the promising ways of discovering promising lead molecules for drug discovery. In recent years, a special class of plant-associated fungi, namely, fungal endophytes, have emerged as an important source of bioactive compounds with unique chemistry and interesting biological activities. The present review focuses on endophytic fungi and their classification, rationale for selection and prioritization of host plants for fungal isolation and examples of strategies that have been adopted to induce the activation of cryptic biosynthetic gene clusters to enhance the biosynthetic potential of fungal endophytes.

Effect of precursor feeding, dietary supplementation, chemical elicitors and co-culturing on resveratrol production by Arcopilus aureus

Resveratrol is an important stilbene, initially identified from red wine possessing immense therapeutic, cosmeceutical and nutraceutical applications. In the present study, endophytic fungus Arcopilus aureus(#12VVLMP) which produces resveratrol extracellularly was selected as a candidate for epigenetic modulation using natural supplements, precursor feeding, chemical elicitors and co-culturing to enhance resveratrol production. The present study highlighted the role of natural supplements i.e. grape seed extract and grape skin extract which constitute grape pomace to enhance resveratrol production by 27.7 and 13.65% respectively. Co-culturing also impacted the resveratrol production by A. aureus, enhancing it by 9.4%. Chemical elicitors and precursor feeding did not induce significant enhancement in resveratrol production. Enhancement of anti-oxidant effect was also observed in the case of use of natural supplements assayed by DPPH and ABTS^• radical scavenging assays. Similarly anti-staphylococcal and anti-candida activities were potentially higher when natural supplements were used followed by co-culturing. These findings indicate that the use of natural supplement which is a by-product of wine industry may be used as a modulator of resveratrol production by A. aureus. This shall lead to a cost-effective fermentation process of resveratrol production, the global demand of which is continuously increasing.

NF-κB inhibitory, antimicrobial and antiproliferative potentials of compounds from Hawaiian fungus Aspergillus polyporicola FS910

Bioassay-guided experimental design and chromatographic analysis led to the isolation and identification of ten compounds (1-10) including two unusual sulfur-containing curvularin macrolides (1 and 2) from a Hawaiian fungal strain Aspergillus polyporicola FS910. Compounds 1 and 2 are rare curvularin macrolides each with a five-membered cyclic sulfur-containing moiety. The structures of the compounds were identified by HRESIMS, NMR spectroscopy, X-ray crystallography, ECD and DFT energy calculation, as well as comparing with previous literatures. Compounds 4, 6 and 8 were active against TNF-α-induced NF-κB inhibitory activity with IC₅₀ values of 26.45, 5.41 and 15.8 µM, respectively. Compounds 3 and 5-8 exhibited anti-proliferative activity against HT1080, T46D, and A2780S cell lines, with IC₅₀ values ranging from 2.48 to 29.17 μM. Additionally, Compound 3 showed promising antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA), Bacillus subtilis, Escherichia coli and Candida albicans. Moreover, when tested in combination with antibiotic adjuvant disulfiram [4 µg/mL], compounds 4, 5 and 10 also displayed significant antibacterial activity against S. aureus.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02877-7.

Discovery and investigation of natural Diels-Alderases

It has been proposed that biosyntheses of many natural products involve pericyclic reactions, including Diels-Alder (DA) reaction. However, only a small set of enzymes have been proposed to catalyze pericyclic reactions. Most surprisingly, there has been no formal identification of natural enzymes that can be defined to catalyze DA reactions (DAases), despite the wide application of the reaction in chemical syntheses of complex organic compounds. However, recent studies began to accumulate a growing body of evidence that supports the notion that enzymes that formally catalyze DA reactions, in fact exist. In this review, I will begin by describing a short history behind the discovery and characterization of macrophomate synthase, one of the earliest enzymes that was proposed to catalyze an intermolecular DA reaction during the biosynthesis of a substituted benzoic acid in a phytopathogenic fungus Macrophoma commelinae. Then, I will discuss representative enzymes that have been chemically authenticated to catalyze DA reactions, with emphasis on more recent discoveries of DAases involved mainly in fungal secondary metabolite biosynthesis except for one example from a marine streptomycete. The current success in identification of a series of DAases and enzymes that catalyze other pericyclic reactions owes to the combined efforts from both the experimental and theoretical approaches in discovering natural products. Such efforts typically involve identifying the chemical features derived from cycloaddition reactions, isolating the biosynthetic genes that encode enzymes that generate such chemical features and deciphering the reaction mechanisms for the enzyme-catalyzed pericyclic reactions.

Bio-Guided Isolation of Antimalarial Metabolites from the Coculture of Two Red Sea Sponge-Derived Actinokineospora and Rhodococcus spp

Coculture is a productive technique to trigger microbes’ biosynthetic capacity by mimicking the natural habitats’ features principally by competition for food and space and interspecies cross-talks. Mixed cultivation of two Red Sea-derived actinobacteria, Actinokineospora spheciospongiae strain EG49 and Rhodococcus sp. UR59, resulted in the induction of several non-traced metabolites in their axenic cultures, which were detected using LC–HRMS metabolomics analysis. Antimalarial guided isolation of the cocultured fermentation led to the isolation of the angucyclines actinosporins E (1), H (2), G (3), tetragulol (5) and the anthraquinone capillasterquinone B (6), which were not reported under axenic conditions. Interestingly, actinosporins were previously induced when the axenic culture of the Actinokineospora spheciospongiae strain EG49 was treated with signalling molecule N-acetyl-d-glucosamine (GluNAc); this finding confirmed the effectiveness of coculture in the discovery of microbial metabolites yet to be discovered in the axenic fermentation with the potential that could be comparable to adding chemical signalling molecules in the fermentation flask. The isolated angucycline and anthraquinone compounds exhibited in vitro antimalarial activity and good biding affinity against lysyl-tRNA synthetase (PfKRS1), highlighting their potential developability as new antimalarial structural motif.

Biological Activities of Some New Secondary Metabolites Isolated from Endophytic Fungi: A Review Study

Secondary metabolites isolated from plant endophytic fungi have been getting more and more attention. Some secondary metabolites exhibit high biological activities, hence, they have potential to be used for promising lead compounds in drug discovery. In this review, a total of 134 journal articles (from 2017 to 2019) were reviewed and the chemical structures of 449 new metabolites, including polyketides, terpenoids, steroids and so on, were summarized. Besides, various biological activities and structure-activity relationship of some compounds were aslo described.

An enzymatic Alder-ene reaction

An ongoing challenge in chemical research is to design catalysts that select the outcomes of the reactions of complex molecules. Chemists rely on organo- or transition metal catalysts to control stereo-, regio-, and periselectivity (selectivity among possible pericyclic reactions). Nature achieves these types of selectivity with a variety of enzymes such as the recently discovered pericyclases – a family of enzymes that catalyze pericyclic reactions.¹ To date, the majority of characterized enzymatic pericyclic reactions are cycloadditions and it has been difficult to rationalize how observed selectivities are achieved.^2-13 We report here the discovery of two homologous groups of pericyclases that catalyze distinct reactions: one group catalyzes an Alder-ene reaction, previously unknown in biology; the second catalyzes a stereoselective hetero-Diels–Alder reaction. Guided by computational studies, we rationalized the observed differences in reactivities and designed mutants that reverse periselectivities from Alder-ene to hetero-Diels–Alder and vice versa. A combination of in vitro biochemical characterizations, computational studies, enzyme co-crystal structures, and mutational studies provide a picture of how high regio- and periselectivities are achieved in nearly identical active sites.

Antibacterial and NF-κB Inhibitory Lumazine Peptides, Aspochalasin, γ-Butyrolactone Derivatives, and Cyclic Peptides from a Hawaiian Aspergillus flavipes

Five new lumazine peptides (1-5), a new aspochalasin derivative (6), and a new γ-butyrolactone derivative (7), together with seven known compounds (8-14), were isolated from a Hawaiian fungal strain, Aspergillus flavipes FS888. Compound 1 is an uncommon natural product containing an isocyano group. The structures of the new compounds 1-7 were elucidated by NMR spectroscopy, HRESIMS, chemical derivatization, and ECD analysis. Compounds 12-14 showed significant antibacterial activity against S. aureus when in combination with disulfiram. Additionally, compounds 9 and 13 showed NF-κB inhibitory activity with IC₅₀ values of 3.1 ± 1.0 and 10.3 ± 2.0 μM, respectively.

Anti-inflammatory, Antiplatelet Aggregation, and Antiangiogenesis Polyketides from Epicoccum sorghinum: Toward an Understating of Its Biological Activities and Potential Applications

The ethyl acetate extract of an endophyte Epicoccum sorghinum exhibited anti-inflammatory activity at a concentration of <10 μg/mL. By bioassay-guided fractionation, one new compound, named epicorepoxydon A (1), and one unusual bioactive compound, 6-(hydroxymethyl)benzene-1,2,4-triol (6), together with six known compounds, were isolated from E. sorghinum. The structures of all isolates were established by spectroscopic analyses. The relative configuration of 1 was deduced by the NOESY spectrum and its absolute configuration was determined by X-ray single-crystal analysis. The biological activities of all isolates were evaluated using four types of bioassays including cytotoxicity, anti-inflammatory, antiplatelet aggregation, and antiangiogenesis activities. Compounds 4 and 6 showed potent anti-inflammatory activity, compound 2 possessed potent antiplatelet aggregation and antiangiogenesis activities, and compound 6 demonstrated antiangiogenesis activity. This fungal species can cause a human hemorrhagic disorder known as onyalai. In this study, we identified the active components with antiplatelet aggregation and antiangiogenesis activities, which may be related to the hemorrhagic disorder caused by this fungus. Moreover, we proposed a biosynthetic pathway of the isolated polyketide secondary metabolites and investigated their structure-activity relationship (SAR). Our results suggested that E. sorghinum is a potent source of biologically active compounds that can be developed as antiplatelet aggregation and anti-inflammatory agents.

Tryptoquivalines W and X, two new compounds from a Hawaiian fungal strain and their biological activities

Two new compounds tryptoquivalines W (1) and X (2) were isolated from a Hawaiian soil fungal strain Aspergillus terreus FS107. The soil sample was collected on the top of Mauna Kea, the tallest mountain in Hawaii. The structures of compounds 1 and 2 were determined on the basis of MS spectroscopic and NMR analysis, and NMR calculation. The absolute configuration (AC) was determined by ECD calculations. Compounds 4 and 5 showed inhibition against NF-κB with IC50 values of 3.45 and 6.76 μM, respectively.

NF-κB Inhibitory and Antibacterial Helvolic and Fumagillin Derivatives from Aspergillus terreus

Two new helvolic acid analogues (1 and 2) and one new fumagillin derivative containing an octahydroisobenzofuran moiety (3), together with four known compounds (4-7), were isolated from an Aspergillus terreus, isolated from soil collected from Mauna Kea, the highest mountain in Hawaii. Compound 4 was recorded in SciFinder with a CAS Registry Number of 1379525-35-5, but it was not documented in the cited reference (ACS Chem. Biol. 2012, 7, 137). The structures of compounds 1-4 were elucidated by NMR spectroscopy and HRMS and ECD analysis. Compounds 5 and 6 showed significant inhibitory activity against NF-κB with IC₅₀ values of 2.7 ± 2.6 and 6.5 ± 0.8 μM, respectively. Compounds 1 and 2 were active against S. aureus with MICs of 6.25 and 6.25 μg/mL, respectively, while compound 5 inhibited E. coli with an MIC of 3.12 μg/mL.

Expanding the chemical diversity through microorganisms co-culture: Current status and outlook

Natural products (NPs) are considered as a cornerstone for the generation of bioactive leads in drug discovery programs. However, one of the major limitations of NP drug discovery program is "rediscovery" of known compounds, thereby hindering the rate of drug discovery efficiency. Therefore, in recent years, to overcome these limitations, a great deal of attention has been drawn towards understanding the role of microorganisms' co-culture in inducing novel chemical entities. Such induction could be related to activation of genes which might be silent or expressed at very low levels (below detection limit) in pure-strain cultures under normal laboratory conditions. In this review, chemical diversity of compounds isolated from microbial co-cultures, is discussed. For this purpose, chemodiversity has been represented as a chemical-structure network based on the "Tanimoto Structural Similarity Index". This highlights the huge structural diversity induced by microbial co-culture. In addition, the current trends in microbial co-culture research are highlighted. Finally, the current challenges (1 - induction monitoring, 2 - reproducibility, 3 - growth time effect and 4 - up-scaling for isolation purposes) are discussed. The information in this review will support researchers to design microbial co-culture strategies for future research efforts. In addition, guidelines for co-culture induction reporting are also provided to strengthen future reporting in this NP field.

Toxic, but beneficial compounds from endophytic fungi of Carica papaya

Fungi remain a promising source of novel biologically active compounds with potentials in drug discovery and development. This study was aimed at investigating the secondary metabolites from endophytic Fusarium equiseti and Epicoccum sorghinum associated with leaves of Carica papaya collected from Agulu, Anambra State, Nigeria. Isolation of the endophytic fungi, taxonomic identification, fermentation, extraction and isolation of fungal secondary metabolites were carried out using standard procedures. Chromatographic separation and spectroscopic analyses of the fungal secondary metabolites yielded three toxigenic compounds - equisetin and its epimer 5’- epiequisetin from F. equiseti and tenuazonic acid from E. sorghinum These compounds are known to possess several beneficial biological properties that can be explored for pharmaceutical, agricultural or industrial purposes.

An Unusual Benzoisoquinoline-9-one Derivative and Other Related Compounds with Antiproliferative Activity from Hawaiian Endophytic Fungus Peyronellaea sp. FT431

A new polyketide containing the benzoisoquinoline-9-one moiety, peyronetide A (1), and three other new derivatives peyronetides B–D (2–4), as well as one known compound (5) were purified from the cultured broth of the endophytic fungus Peyronellaea sp. FT431, which was isolated from the Hawaiian indigenous plant, Verbena sp. The structures of the new compounds were determined through the analysis of HRMS and NMR spectroscopic data. Compounds 1, 2, and 5 showed cytotoxic activities against TK-10 (human kidney adenocarcinoma cells), cisplatin sensitive A2780S (human ovarian carcinoma cells), and cisplatin resistant A2780CisR cell lines, with IC₅₀ values between 6.7 to 29.2 μM.

Bacillus amyloliquefaciens induces production of a novel blennolide K in coculture of Setophoma terrestris

AIMS

The discovery of known bioactive chemical leads from microbial monocultures hinders the efficiency of drug discovery programmes. Therefore, in recent years, the use of fungal-bacterial coculture experiments has gained considerable attention due to their ability to generate new bioactive leads. In this work, fungal strain Setophoma terrestris was cocultured with Bacillus amyloliquifaciens to discover novel bioactive compounds.

MATERIALS AND METHODS

The bioactive methanolic coculture extract was chosen for the isolation of compounds by chromatographic methods. The isolated compounds were characterized by NMR and mass spectrometric techniques.

CONCLUSION

Coculture extract has resulted in the production of five blennolides. The novel compound, blennolide K was found active against PC-3 (prostate) and MCF-7 (breast) cell lines with an IC₅₀ value of 3·7 ± 0·6 and 4·8 ± 0·4 μmol l^-1 respectively. Furthermore, the nuclear morphology study in PC-3 cells after treatment with blennolide K, demonstrated chromatin condensation, formation of apoptotic bodies and shrinkage of cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

To our knowledge, only few studies have reported the induction of bioactive compounds by coculture having long-distance inhibition morphology. This is principally due to the low occurrences of such morphology. Our study demonstrates the impact of coculture on production of new chemical leads in drug discovery programmes.