Secondary Metabolites and PI3K Inhibitory Activity of Colletotrichum gloeosporioides, a Fungal Endophyte of Uncaria rhynchophylla

Chemical Diversity, Pharmacology, Synthesis and Detection of Naturally Occurring Peroxides

Natural occurring peroxides are interesting bioprospecting targets due to their molecular structural diversity and the wide range of pharmacological activities. In this systematic review, a total of 123 peroxide compounds were analysed from 99 published papers with the compounds distributed in 31 plants, 18 animals and 41 microorganisms living in land and water ecosystems. The peroxide moiety exists as both cyclic and acyclic entities and can include 1,2-dioxolanes, 1,2-dioxane rings and common secondary metabolites with a peroxo group. These peroxides possessed diverse bioactivities including anticancer, antimalarial, antimicrobial, anti-inflammatory, neuroprotective, adipogenic suppressor, antituberculosis, anti-melanogenic and anti-coagulant agents. Biosynthetic pathways and mechanisms of most endoperoxides have not been well established. Method development in peroxide detection has been a challenging task requiring multidisciplinary investigation and exploration on peroxy-containing secondary metabolites are necessary.

Exploring the antioxidant potential of endophytic fungi: a review on methods for extraction and quantification of total antioxidant capacity (TAC)

Endophytic fungi have emerged as a significant source of natural products with remarkable bioactivities. Recent research has identified numerous antioxidant molecules among the secondary metabolites of endophytic fungi. These organisms, whether unicellular or micro-multicellular, offer the potential for genetic manipulation to enhance the production of these valuable antioxidant compounds, which hold promise for promoting health, vitality, and various biotechnological applications. In this study, we provide a critical review of methods for extracting, purifying, characterizing, and estimating the total antioxidant capacity (TAC) of endophytic fungi metabolites. While many endophytes produce metabolites similar to those found in plants with established symbiotic associations, we also highlight the existence of novel metabolites with potential scientific interest. Additionally, we discuss how advancements in nanotechnology have opened new avenues for exploring nanoformulations of endophytic metabolites in future studies, offering opportunities for diverse biological and industrial applications.

Secondary metabolites and transcriptomic analysis of novel pulcherrimin producer Metschnikowia persimmonesis KIOM G15050: A potent and safe food biocontrol agent

Metschnikowia persimmonesis, a novel endophytic yeast strain isolated from Diospyros kaki calyx, possesses strong antimicrobial activity. We investigated its potential use as an environmentally safe food biocontrol agent through genomics, transcriptomics, and metabolomics. Secondary metabolites were isolated from M. persimmonesis, followed by chemical structure elucidation, PUL gene cluster identification, and RNA sequencing. Pulcherrimin was isolated using 2 M NaOH, its structure was confirmed, and the yield was quantified. Biocontrol efficacy of M. persimmonesis on persimmon fruits and calyx was evaluated by assessing lesion diameter and disease incidence. Following compounds were isolated from M. persimmonesis co-culture with Botrytis cinerea and Fusarium oxysporum: fusaric acid, benzoic acid, benzeneacetic acid, 4-hydroxybenzeneacetic acid, 4-(-2-hydoxyethyl)-benzoic acid, cyclo (Leu-Leu), benzenemethanol, 4-hydroxy-benzaldehide, 2-hydroxy-4-methoxy-benzoic acid, 4-hydroxy-benzoic acid, lumichrome, heptadecanoic acid, and nonadecanoic acid. Exposing M. persimmonesis to different growth media conditions (with or without sugar) resulted in the isolation of five compounds: Tyrosol, Cyclo (Pro-Val), cyclo(L-Pro-L-Tyr), cyclo(Leu-Leu), and cyclo(l-tyrosilylicine). Differentially expressed gene analysis revealed 3264 genes that were significantly expressed (fold change ≥2 and p-value ≤0.05) during M. persimmonesis growth in different media, of which only 270 (8.27%) showed altered expression in all sample combinations with Luria-Bertani Agar as control. Minimal media with ferric ions and tween-80 triggered the most gene expression changes, with the highest levels of PUL gene expression and pulcherrimin yield (262.166 mg/L) among all media treatments. M. persimmonesis also produced a higher amount of pulcherrimin (209.733 mg/L) than Metschnikowia pulcherrima (152.8 mg/L). M. persimmonesis inhibited the growth of Fusarium oxysporum in persimmon fruit and calyx. Toxicity evaluation of M. persimmonesis extracts showed no harmful effects on the liver and mitochondria of zebrafish, and no potential risk of cardiotoxicity in hERG-HEK293 cell lines. Thus, M. persimmonesis can be commercialized as a potent and safe biocontrol agent for preserving food products.

Diversity of Mycotoxins and Other Secondary Metabolites Recovered from Blood Oranges Infected by Colletotrichum, Alternaria, and Penicillium Species

This study identified secondary metabolites produced by Alternaria alternata, Colletotrichum gloeosporioides, and Penicillium digitatum in fruits of two blood orange cultivars before harvest. Analysis was performed by UHPLC-Q-TOF-MS. Three types of fruits were selected, asymptomatic, symptomatic showing necrotic lesions caused by hail, and mummified. Extracts from peel and juice were analyzed separately. Penicillium digitatum was the prevalent species recovered from mummified and hail-injured fruits. Among 47 secondary metabolites identified, 16, 18, and 13 were of A. alternata, C. gloeosporioides, and P. digitatum, respectively. Consistently with isolations, indicating the presence of these fungi also in asymptomatic fruits, the metabolic profiles of the peel of hail-injured and asymptomatic fruits did not differ substantially. Major differences were found in the profiles of juice from hail-injured and mummified fruits, such as a significant higher presence of 5,4-dihydroxy-3,7,8-trimethoxy-6C-methylflavone and Atrovenetin, particularly in the juice of mummified fruits of the Tarocco Lempso cultivar. Moreover, the mycotoxins patulin and Rubratoxin B were detected exclusively in mummified fruits. Patulin was detected in both the juice and peel, with a higher relative abundance in the juice, while Rubratoxin B was detected only in the juice. These findings provide basic information for evaluating and preventing the risk of contamination by mycotoxins in the citrus fresh fruit supply chain and juice industry.

Endophytic fungi mediates production of bioactive secondary metabolites via modulation of genes involved in key metabolic pathways and their contribution in different biotechnological sector

Endophytic fungi stimulate the production of an enormous number of bioactive metabolites in medicinal plants and affect the different steps of biosynthetic pathways of these secondary metabolites. Endophytic fungi possess a number of biosynthetic gene clusters that possess genes for various enzymes, transcription factors, etc., in their genome responsible for the production of secondary metabolites. Additionally, endophytic fungi also modulate the expression of various genes responsible for the synthesis of key enzymes involved in metabolic pathways of such as HMGR, DXR, etc. involved in the production of a large number of phenolic compounds as well as regulate the expression of genes involved in the production of alkaloids and terpenoids in different plants. This review aims to provide a comprehensive overview of gene expression related to endophytes and their impact on metabolic pathways. Additionally, this review will emphasize the studies done to isolate these secondary metabolites from endophytic fungi in large quantities and assess their bioactivity. Due to ease in synthesis of secondary metabolites and their huge application in the medical industry, these bioactive metabolites are now being extracted from strains of these endophytic fungi commercially. Apart from their application in the pharmaceutical industry, most of these metabolites extracted from endophytic fungi also possess plant growth-promoting ability, bioremediation potential, novel bio control agents, sources of anti-oxidants, etc. The review will comprehensively shed a light on the biotechnological application of these fungal metabolites at the industrial level.

Lentinuses A-B, two alkaloids from the marine-derived fungus Lentinus sajor-caju with potent anti-pulmonary fibrosis activity

By adding natural amino acids into the medium as sole nitrogen source, twenty-four compounds, including two new alkaloids lentinuses A-B (1-2) with a rare oxazinone core in marine natural products, one new natural product 3-acetamido-4-phenylfurazan (3), 9β-ergosterol (22) were firstly discovered from a marine fungus, and twenty known compounds (4-21, 23-24) were isolated from the marine-derived fungus Lentinus sajor-caju. The chemical structures of all these compounds were elucidated by HRMS, NMR spectroscopy and X-ray diffraction. Compounds 1-24 were evaluated for their inhibitory activity against TGF-β1-induced collagen accumulation in human fetal lung fibroblasts (HFL1). Compounds 2, 3, 12, 22, and 23 showed potent activity against TGF-β1-induced collagen accumulation and low toxicity to HFL1 cells. The binding mode of lentinus B (2) with TGF-β1 receptor was then performed by using Schrödinger software, and the result showed that lentinus B possesses a strong binding force such as hydrogen bonding and hydrophobic interactions to the protein, which may provide a theoretical basis to design more potent anti-fibrotic drugs in the future.

Isolation, purification, and structural elucidation of Mellein from endophytic fungus Lasiodiplodia theobromae strain (SJF-1) and its broad-spectrum antimicrobial and pharmacological properties

In an ongoing investigation of bioactive metabolites producing potential endophytic fungi, the strain Lasiodiplodia theobromae (SJF-1) was isolated from a medicinal plant Syzygium cumini. The cultural, morphological, and molecular identification was done with the SJF-1 strain. The obtained gene sequence was deposited in NCBI with accession number MG 938644. The methanolic extract of SJF-1 strain possessed one major bioactive fraction and it was purified by column chromatography. Further, it was identified as Mellein by various spectroscopic studies (¹ H, ¹³ C, DEPT-135°, FT-IR, ESI-HR-MS, and 2D NMR). Biologically, Mellein showed potent anti-Xanthomonas activity with MIC values ranging from 1.9-62.5 μgml^-1 against eleven Xanthomonas strains; a broad-spectrum antimicrobial activity with MIC 7.8-31.25 μgml^-1 and 1.9-31.25 μgml^-1 towards both bacterial and fungal strains respectively. The SEM analysis proved the anti-microbial efficacy of a Mellein by rupturing the cell walls of Xanthomonas sp. Molecular docking studies further supported that the Mellein showed good binding interactions with the proteins of Xanthomonas sp. to reduce pathogenicity. Further, in silico pharmacological studies showed that this metabolite exhibited high gastrointestinal absorption properties and promising oral drug bioavailability. We report, anti-Xanthomonas, in silico docking, and pharmacological studies of Mellein from (SJF-1) strain for the first time.

α-Glucosidase inhibitory effect of an anthraquinonoid produced by Fusarium incarnatum GDZZ-G2

α-Glucosidase is the key enzyme on carbohydrate metabolism, and its bioactive inhibitors are supposed to be an effective therapeutic for type 2 diabetes mellitus. During our continuing study for discovering α-glucosidase inhibitors, a fungus GDZZ-G2 which is derived from a medicinal plant Callicarpa kwangtungensis Chun, exhibited significant inhibition on α-glucosidase. The strain was identified as Fusarium incarnatum by morphological and molecular methods. Further bioassay-guided fractionation result in six known secondary metabolites (1-6). All the compounds except 4 were isolated from F. incarnatum for the first time. Among them, an anthraquinonoid (S)-1,3,6-trihydroxy-7-(1-hydroxyethyl)anthracene-9,10-dione (compound 1) exhibited strong inhibitory effect against α-glucosidase (IC₅₀  = 77.67 ± 0.67 μΜ), compared with acarbose (IC₅₀  = 711.8 ± 5 μΜ). An enzyme kinetics analysis revealed that compound 1 was an uncompetitive inhibitor. Besides, docking simulations predicted that compound 1 inhibited α-glucosidase substrate complex by binding Gln322, Gly306, Thr307, and Ser329 through hydrogen-bond interactions. Our findings suggested that compound 1 can be considered a lead compound for further modifications and the development of a new effective drug candidate in the treatment of type 2 diabetes mellitus.

Secondary metabolites with diversified structures from an endophytic fungus Colletotrichum gloeosporioides associated with a toxic medicinal plant Tylophora ovata

Six new secondary metabolites, including two new nor-triterpenes (1 and 2), one new sesquiterpene (4), two new α-pyrone derivatives (6 and 7), and one new natural product (5) along with two known compounds (3 and 8) were isolated from an endophytic fungus Colletotrichum gloeosporioides obtained from a toxic medicinal plant Tylophora ovata. Their structures were elucidated by spectroscopic data analyses, while their absolute configurations were determined by CD and X-ray diffraction analyses. The in vitro anti-inflammatory activities of these compounds were evaluated.

Bioprospecting of fungal endophytes from Oroxylum indicum (L.) Kurz with antioxidant and cytotoxic activity

Oroxylum indicum (L.) Kurz, a medicinal plant, shows numerous pharmacological properties which may be attributed to the bioactive compounds produced by O. indicum or due to associated endophytes. In the present study, leaf of O. indicum was evaluated for the presence of associated fungal endophytes, and antioxidant and cytotoxic activities of bioactive compounds produced from them. Using culture-dependent approach, eight fungal endophytes belonging to five different genera were identified. Two endophytes Daldinia eschscholtzii and Ectophoma multirostrata have been reported for the first time from the leaf of O. indicum plant. High-performance thin-layer chromatography (HPTLC) of ethyl acetate (EA) extract of isolated fungal endophytes showed a distinct fingerprinting profile in EA extract of Colletotrichum gloeosporioides. Among identified endophytes, EA extract of C. gloeosporioides showed significant antioxidant activity against DPPH free radical, superoxide anion radical, nitric oxide radical and hydroxyl radical with EC50 values of 22.24±1.302 μg/mL, 67.46±0.576 μg/mL, 80.10±0.706 μg/mL and 61.55±1.360 μg/mL, respectively. EA extract of C. gloeosporioides exhibited potential cytotoxicity against HCT116, HeLa and HepG2 cancer cell lines with IC50 values of 76.59 μg/mL, 176.20 μg/mL and 1750.70 μg/mL, respectively. A comparative HPTLC fingerprinting and the antioxidant activity of C. gloeosporioides associated with two different hosts (leaf of O. indicum and dead twigs of other plant) showed that C. gloeosporioides produces bioactive compounds in a host-dependent manner.

Determination of Community Structure and Diversity of Seed-Vectored Endophytic Fungi in Alpinia zerumbet

Endophytic fungi act as seed endosymbiont, thereby playing a very crucial role in the growth and development of seeds. Seed-vectored endophytic fungi establish an everlasting association with seeds and travel from generation to generation. To explore the composition and diversity of endophytic fungi in Alpinia zerumbet seeds, high-throughput Illumina MiSeq sequencing was employed for the following stages: fruit formation period (YSJ1), young fruit period (YSJ2), early mature period (YSJ3), middle mature period (YSJ4), and late mature period (YSJ5). A total of 906,694 sequence reads and 745 operational taxonomic units (OTUs) were obtained and further classified into 8 phyla, 30 classes, 73 orders, 163 families, 302 genera, and 449 species. The highest endophytic fungal diversity was observed at YSJ5. The genera with the highest abundance were Cladosporium, Kodamaea, Hannaella, Mycothermus, Gibberella, Sarocladium, and Neopestalotiopsis. Functional Guild (FUNGuild) analysis revealed that endophytic fungi were undefined saprotroph, plant pathogens, animal pathogen–endophyte–lichen parasite–plant pathogen–wood saprotroph, and soil saprotrophs. Alternaria, Fusarium, Cladosporium, and Sarocladium, which are potential probiotics and can be used as biocontrol agents, were also abundant. This study is part of the Sustainable Development Goals of United Nations Organization (UNO) to “Establish Good Health and Well-Being.”

Isolation of Taxol and Flavin-like fluorochrome from Endophytic Fungi of Mangifera indica

Scouting for novel and plant-derived biomolecules from endophytic microbial sources draws greater focus on the discovery of novel bioactive metabolites. With this rationale, we scouted the endophytic fungi for taxol, an anticancer diterpenoid and fluorescent biomolecules. In the present study, about 31 endophytic fungal isolates recovered from the Mangifera indica leaves were screened for taxol production in M1D medium. About five isolates were shortlisted based on the thin layer chromatographic analysis of the fungal extracts. Among them Colletotrichum sp. MIP-5 has been identified as a producer of fungal taxol based on UV, FTIR, TLC and HPLC analysis. The partially purified fungal taxol showed similar spectral and chromatographic features of commercially available paclitaxel. In addition to this, we also report the production of a fluorescent compound by Penicillium sp. MIP-3. The Flavin-like compound exhibited a bright greenish-yellow fluorescence with an emission maximum in the range of 505 – 545nm. GC-MS analysis showed the occurrence of Latia luciferin, primarily associated with the bioluminescence of freshwater limpet Latia neritoides. This is the first report of this compound from Penicillium sp. In addition, therapeutically active steroid (β-Sitosterol, Stigmasterol, Campesterol), quinones (Benzo[h]quinoline, 2,4-dimethyl-) and phloroglucinol (Aspidinol) derivatives were also identified from Penicillium sp. MIP-3 based on GC-MS analysis. These molecules could potentially be used in biological and pharmaceutical applications in future.

Simultaneous Determination of Six Uncaria Alkaloids in Mouse Blood by UPLC-MS/MS and Its Application in Pharmacokinetics and Bioavailability

A specific ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method has been developed for the simultaneous determination of six Uncaria alkaloids in mouse blood with midazolam as the internal standard (IS). Only 20 μL blood was needed for sample preparation, and the protein was precipitated with acetonitrile. The UPLC BEH C18 column (2.1 mm × 100 mm, 1.7 μm) was used for chromatographic separation. The mobile phase consisted of 0.1% formic acid and acetonitrile with gradient elution within 5.5 min. Multiple reaction monitoring (MRM) and the positive electrospray ionization model were used for quantitative analysis. The accuracy of the UPLC-MS/MS method ranged from 86.5% to 110.4%. The precision for intraday and interday was ≤15% each. The mean recovery and the matrix effects were found to be 64.4-86.8% and 94.1-109.4%, respectively. The calibration curves in blood were linear in the range of 1-1000 ng/mL with a favorable correlation coefficient (r²) of 0.995. The pharmacokinetic results showed that six Uncaria alkaloids metabolized rapidly in mice with a half-life between 0.6 h and 4.4 h. The bioavailability of corynoxeine, isocorynoxeine, rhynchophylline, isorhynchophylline, hirsutine, and hirsuteine was 27.3%, 32.7%, 49.4%, 29.5%, 68.9%, and 51.0%, respectively, which showed satisfactory oral absorption of each alkaloid.

Natural Products from Endophytic Fungi Associated with Rubiaceae Species

This review presents the chemical diversity and pharmacological properties of secondary metabolites produced by endophytic fungi associated with various genera of Rubiaceae. Several classes of natural products are described for these endophytes, although, this study highlights the importance of some metabolites, which are involved in antifungal, antibacterial, anti-protozoal activities; neurodegenerative diseases; cytotoxic activity; anti-inflammatory and antioxidant activity; and hyperglycemic control.

Melleins-Intriguing Natural Compounds

Melleins are 3,4-dihydroisocoumarins mainly produced by fungi, but also by plants, insects and bacteria. These specialized metabolites play important roles in the life cycles of the producers and they are involved in many biochemical and ecological processes. This review outlines the isolation and chemical and biological characterizations of natural-occurring melleins from the first report of (R)-mellein in 1933 to the most recent advances in their characterization in 2019. In addition, the pathways that could be involved in mellein biosynthesis are discussed, along with the enzymes and genes involved.

Metabolites from Two Dominant Thermophilic Fungal Species Thermomyces lanuginosus and Scytalidium thermophilum

Thermomyces lanuginosus and Scytalidium thermophilum are among the most ubiquitous thermophilic fungi in compost and soil. Chemical study on these two prevalent strains collected from Yunnan led to isolation of 23 metabolites, including one new metabolite, therlanubutanolide, and 15 known compounds, isolated from the YGP culture broth of Thermomyces lanuginosus and 7 known compounds isolated from Scytalidium thermophilum, respectively. Therlanubutanolide shared the quite similar features of the same carbon skeleton and saturation as natural hexadecanoic acids. This was the first reported discovery of such a lactone as natural occurring metabolite. All the compounds were reported for the first time from thermophilic fungi. Among them, N-[(2S,3R,4E,8E)-1,3-dihydroxy-9-methyloctadeca-4,8-dien-2-yl]acetamide was for the first time reported to be a naturally occurring metabolite and its NMR data was first provided in this study. A type of PKS-derived metabolites, three 3,4-dihydronaphthalen-1(2H)-ones, which were widely found in plant pathogenic fungi as phytotoxins and reported to have antimicrobial activity, were obtained from both dominant thermophilic fungi. The frequent occurrence of such PKS phytotoxins in these two thermophilic fungi might suggest particular ecological interest.

Uncarialins A-I, Monoterpenoid Indole Alkaloids from Uncaria rhynchophylla as Natural Agonists of the 5-HT1A Receptor

Nine new monoterpenoid indole alkaloids, uncarialins A-I (1-9), were isolated from Uncaria rhynchophylla as well as 14 known analogues (10-23). Their structures were determined by HRESIMS, 1D and 2D NMR, and experimental and calculated electronic circular dichroism data. Compounds 5, 7, 15, and 22 displayed significant agonistic effects against the 5-HT_1A receptor with EC₅₀ values of 2.2 ± 0.1, 0.1 ± 0.1, 1.6 ± 0.3, and 2.0 ± 0.5 μM, respectively. The mechanisms of action of these four compounds with the 5-HT_1A receptor were investigated by molecular docking, and the results suggested that amino acid residues Asp116, Thr196, Asn386, and Tyr390 played critical roles in the observed activity of the above-mentioned compounds.