Structurally Uncommon Secondary Metabolites Derived from Endophytic Fungi

A Close View of the Production of Bioactive Fungal Metabolites Mediated by Chromatin Modifiers

Secondary metabolites produced by fungi are well known for their biological properties, which play important roles in medicine. These metabolites aid in managing infections and treating chronic illnesses, thereby contributing substantially to human health improvement. Despite this extensive knowledge, the vast biodiversity and biosynthetic potential of fungi is still largely unexplored, highlighting the need for further research in natural products. In this review, several secondary metabolites of fungal origin are described, emphasizing novel structures and skeletons. The detection and characterization of these metabolites have been significantly facilitated by advancements in analytical systems, particularly modern hyphenated liquid chromatography/mass spectrometry. These improvements have primarily enhanced sensitivity, resolution, and analysis flow velocity. Since the in vitro production of novel metabolites is often lower than the re-isolation of known metabolites, understanding chromatin-based alterations in fungal gene expression can elucidate potential pathways for discovering new metabolites. Several protocols for inducing metabolite production from different strains are discussed, demonstrating the need for uniformity in experimental procedures to achieve consistent biosynthetic activation.

Terricoxanthones A-E, unprecedented dihydropyran-containing dimeric xanthones from the endophytic fungus Neurospora terricola HDF-Br-2 associated with the vulnerable conifer Pseudotsuga gaussenii

An investigation on the secondary metabolites from a rice culture broth of the endophytic fungus Neurospora terricola HDF-Br-2 derived from the vulnerable conifer Pseudotsuga gaussenii led to the isolation and characterization of 34 structurally diverse polyketides (1-34). Seven of them are previously undescribed, including five unprecedented dihydropyran-containing (terricoxanthones A-E, 1-5, resp.) and one rare tetrahydrofuran-containing (terricoxanthone F, 6) dimeric xanthones. The structures were elucidated by spectroscopic methods and single-crystal X-ray diffraction analyses. Terricoxanthones each were obtained as a racemic mixture. Their plausible biosynthetic relationships were briefly proposed. Compounds 6, aspergillusone A (8), and alatinone (27) displayed considerable inhibition against Candida albicans with MIC values of 8-16 μg/mL. 4-Hydroxyvertixanthone (12) and 27 exhibited significant inhibitory activities against Staphylococcus aureus, with MIC values of 4-8 μg/mL. Furthermore, compounds 8 and 27 could disrupt biofilm of S. aureus and C. albicans at 128 μg/mL. The findings not only extend the skeletons of xanthone dimers and contribute to the diversity of metabolites of endophytes associated with the endangered Chinese conifer P. gaussenii, but could further reveal the important role of protecting plant species diversity in support of chemical diversity and potential sources of new therapeutics.

Aspertaichamide a, a novel cytotoxic prenylated indole alkaloid possessing a bicyclo[2.2.2]diazaoctane framework from a marine algal-derived endophytic fungus aspergillus taichungensis 299

Filamentous fungi belonging to the genus Aspergillus are prodigious producers of alkaloids, particularly prenylated indole alkaloids, that often exhibit structurally diversified skeletons and potent biological activities. In this study, five prenylated indole alkaloids possessing a bicyclo[2.2.2]diazaoctane core ring system, including a novel derivative, namely aspertaichamide A (1), as well as four known compounds, (+)-stephacidin A (2), sclerotiamide (3), (-)-versicolamide B (4), and (+)-versicolamide B (5), were isolated and identified from A. taichungensis 299, an endophytic fungus obtained from the marine red alga Gelidium amansii. The chemical structures of the compounds were elucidated by comprehensive NMR and HRESIMS spectroscopic analyses. In addition to the previously reported prenylated indole alkaloids, aspertaichamide A (1) was characterized as having an unusual ring structure with the fusion of a 3-pyrrolidone dimethylbenzopyran to the bicyclo[2.2.2]diazaoctane moiety, which was rare in these kinds of compounds. The absolute configuration of 1 was determined by TDDFT-ECD calculations. In vitro cytotoxic assays revealed that the novel compound 1 possessed selective cytotoxic activity against five human tumor cell lines (A549, HeLa, HepG2, HCT-116, and AGS), with IC50 values of 1.7-48.5 μM. Most importantly, compound 1 decreased the viability of AGS cells in a concentration-dependent manner with an IC50 value of 1.7 μM. Further studies indicated that 1 may induce AGS cells programmed cell death via the apoptotic pathway.

Two pairs of 2-pyrone enantiomers and a benzophenone analogue from the endophytic fungus Penicillium egyptiacum

Four new 2-pyrone derivatives, two pairs of enantiomers, (±)-egypyrone A [(±)-1] and (±)-egypyrone B [(±)-2], together with a new benzophenone analogue, orbiophenone B (3), were isolated from the endophytic fungus Penicillium egyptiacum. The enantiomeric mixtures (±)-1 and (±)-2 were separated through chiral HPLC, respectively. Their structures were elucidated by extensive analysis of spectroscopic data and the absolute configuration was determined by comparing the optical rotation of structurally similar molecule. Subsequently, the cytotoxic activities of (±)-1, (±)-2, and 3 against the U87 cell line were tested and no activity was observed at a concentration of 10 µM.

Antibacterial, antibiofilm, and antivirulence effects of nanoparticles synthesized from Colletotrichum gloeosporioides in pathogenic E.coli

Antimicrobial resistance is a global problem and antibiotics are becoming ineffective due to the resistance developed by bacteria. In this current research, silver nanoparticles were synthesized from aqueous extract of endophytic fungi Colletotrichum gloeosporioides (CgAgNPs) and characterized by various methods. CgAgNPs efficacy was analyzed by performing antimicrobial assays in Escherichia coli ATCC 25922 and antibiotic resistant pathogenic strains. Upon treatment with CgAgNPs biofilm formation was reduced in all E.coli strains. In vitro cytotoxicity assays revealed that CgAgNPs were able to increase the membrane permeability and induced leakage of sugars and proteins. CgAgNPs induced oxidative stress in E. coli strains led to lipid peroxidation and release of malonaldehyde. The CgAgNPs were able to modulate the anti-oxidant system of cells hence there was a reduction in Glutathione reductase, Catalase and Superoxide dismutase enzymes activities. Analysis of expression of gene encoding CTX-M-15 showed the down regulation upon treatment with ampicillin and CgAgNPs. Overall, the results suggest that CgAgNPs control growth, biofilm formation in E. coli through induction of oxidative stress, interference with antioxidant enzymes, cell content leakage and finally downregulating the virulence gene by interfering with transcription and translation in E. coli. In future, CgAgNPs can be incorporated in formulations to break antibiotic resistance in antibiotic resistant pathogenic E. coli.

Biochemical Screening, Fabrication of Green Nanoparticles and Its Antimicrobial, and Antioxidant Studies of Endophytic Fungus Phlebia Species

Endophytes are organism dwelling totally dynamic and novel biotopes this makes them able to produce novel biochemicals that may become assets to the future. This study aims at understanding the biochemical components of the endophytic fungus Phlebia sp. synthesis of gold and silver nanoparticles from it, and the antimicrobial as well as antioxidant ability of these green synthesised nanoparticles. Aqueous fungal extract was subjected for HRLCMS analysis which revealed 34 biochemicals within the extract. Silver and gold nanoparticles were also produced from the fungal extract. UV-vis analysis revealed a peak at 450 nm for silver nanoparticle and 550 nm for gold nanoparticles. FESEM analysis confirmed the presence of these nanoparticles with its spherical shape. Both of these nanoparticles were able to produce a conspicuous zone of inhibition in the antimicrobial tests against Escherichia coli, Salmonella paratyphi. For both of the organisms under study, a concentration-dependent expansion of the zone of inhibition was discovered in the nanoparticles. However, with silver nanoparticles, a relatively high zone of inhibition and vulnerability of the organism was discovered. Four in vitro free radical scavenging assays, including the DPPH, Hydroxyl, Superoxide, and Nitric oxide radical scavenging assays, were used for antioxidant analysis. The results of every test demonstrated that green synthesised silver nanoparticles had higher activity than gold nanoparticles. All of the tests showed that silver nanoparticles were more active than gold nanoparticles with the maximum value of 86.254 ± 0.296% being discovered at the greatest concentration of superoxide radical scavenging assay.

Recent Updates on the Antimicrobial Compounds from Marine-Derived Penicillium fungi

In this review, 72 compounds isolated from marine-derived Penicillium fungi and their antimicrobial activities are reviewed from 2020 to 2023. According to their structures, these compounds can be divided into terpenoids, polyketides, alkaloids and other structural compounds, among which terpenoids and polyketides are relatively large in number. Some compounds have powerful inhibitory effects against different pathogenic bacteria and fungi. This review aims to provide more useful information and enlightenment for further efficient utilization of Penicillium spp. and their secondary metabolites.

The antifungal properties of terpenoids from the endophytic fungus Bipolaris eleusines

A series of terpenoids (1-17), comprising six new compounds designated bipolariterpenes A-F (1-6) and eleven recognized compounds (7-17), were isolated from the wheat culture of the potato endophytic fungus Bipolaris eleusines. Their structures and stereochemistry were clarified by HRESIMS, NMR, DP4 + probability analyses, and computations for electronic circular dichroism (ECD). All compounds are made up of six meroterpenoids, four sesterterpenes and seven sesquiterpenes. Among them, four sesterterpenes (4, 5, 10, 11) were investigated for their antifungal, antibacterial and cytotoxic properties, and six meroterpenoids (1-3, 7-9) were evaluated for their antifungal properties. The compounds 7, 9, and 10 had substantial antifungal activity against Epidermophyton floccosum at a concentration of 100 µM. No antibacterial and cytotoxic activities were observed.

Structurally diverse indole alkaloids with cytotoxicity from Lonicera Japonica-associated endophytic fungus Penicillium ochrochloron YT2022-65

Natural products, especially fungal secondary metabolites, have been served as valuable sources of drug leads in pharmaceutical industry. Medicinal plants-associated endophytic fungi possess a well-developed secondary metabolism. In this study, chemical investigation on Penicillium ochrochloron YT2022-65, an endophytic fungus associated with Lonicera Japonica, led to the isolation of six structurally diversified indole alkaloids, including a new one, namely peniochroloid A (1), as well as five previously reported alkaloids, flavonoid B (2), brocaeloid C (3), isoroquefortine C (4), roquefortine C (5), and dihydrocarneamide A (6). Their structures, including the absolute configuration of 1, were determined by a combined analysis of HRESIMS, NMR spectroscopic data, and calculation of the optical rotation. Their cytotoxicity against A549, HepG2, MCF-7, and THP-1 cell lines were evaluated in vitro. The new compound 1 was found to possess considerable cytotoxicity against MCF-7 and THP-1 cell lines with IC50 values of 10.2 and 11.0 μM, respectively.

Steccherins A-D, chamigrane-type sesquiterpenes from the fungus Steccherinum ochraceum with selective inhibition on B lymphocyte proliferation

Four previously undescribed chamigrane sesquiterpenes, namely steccherins A-D, have been isolated from the fungus Steccherinum ochraceum. Their structures were elucidated by extensive spectroscopic analysis, as well as computational methods and single crystal X-ray diffraction. Steccherins A and B possess previously undescribed backbones which might be derived from normal chamigrane sesquiterpenes, especially that steccherin A possesses a spiro[5.6]dodecane carbon skeleton via a ring-rearrangement. Steccherins A, C, and D showed immunosuppressive activity with IC50 values ranging from 6.2 to 37.8 μM. The data suggested that these chamigrane sesquiterpenes have potential selective inhibition on LPS-induced B lymphocyte proliferation.

Bioactive Steroids Bearing Oxirane Ring

This review explores the biological activity and structural diversity of steroids and related isoprenoid lipids, with a particular focus on compounds containing an oxirane ring. These natural compounds are derived from fungi, fungal endophytes, as well as extracts of plants, algae, and marine invertebrates. To evaluate their biological activity, an extensive examination of refereed literature sources was conducted, including in vivo and in vitro studies and the utilization of the QSAR method. Notable properties observed among these compounds include strong anti-inflammatory, antineoplastic, antiproliferative, anti-hypercholesterolemic, antiparkinsonian, diuretic, anti-eczematic, anti-psoriatic, and various other activities. Throughout this review, 3D graphs illustrating the activity of individual steroids are presented, accompanied by images of selected terrestrial or marine organisms. Furthermore, this review provides explanations for specific types of biological activity associated with these compounds. The data presented in this review are of scientific interest to the academic community and carry practical implications in the fields of pharmacology and medicine. By analyzing the biological activity and structural diversity of steroids and related isoprenoid lipids, this review offers valuable insights that contribute to both theoretical understanding and applied research. This review draws upon data from various authors to compile information on the biological activity of natural steroids containing an oxirane ring.

Identification of Secondary Metabolites from the Mangrove-Endophyte Lasiodiplodia iranensis F0619 by UPLC-ESI-MS/MS

Lasiodiplodia is a widely distributed fungal genus, frequently found in tropical and subtropical regions where it can cause disease in important crops. It represents a promising source of active secondary metabolites with uses in chemical, pharmaceutical, and agrochemical processes. In this study, the strain Lasiodiplodia iranensis F0619 was isolated from the mangrove Avicennia ger-minans, collected from Sarigua National Park in the Republic of Panama. Fractions of crude extract were analyzed by UPLC-ESI-MS/MS, and five compounds, previously reported from Lasiodiplodia genus were identified, including 11,12-didehydro-7-iso-jasmonic acid (1), 4,5-didehydro-7-iso-jasmonic acid (2), cyclo-(L-Leu-L-Pro) (3), jasmonate-threonine (4), and abscisic acid (5). We describe and analyze their MS/MS fragmentation patterns to confirm the compounds 'chemical structures.

Discovery and Characterization of a Myxobacterial Lanthipeptide with Unique Biosynthetic Features and Anti-inflammatory Activity

The genomes of myxobacteria harbor a variety of biosynthetic gene clusters encoding numerous secondary metabolites, including ribosomally synthesized and post-translationally modified peptides (RiPPs) with diverse chemical structures and biological activities. However, the biosynthetic potential of RiPPs from myxobacteria remains barely explored. Herein, we report a novel myxobacteria lanthipeptide myxococin identified from Myxococcus fulvus. Myxococins represent the first example of lanthipeptides, of which the characteristic multiple thioether rings are installed by employing a Class II lanthipeptide synthetase MfuM and a Class I lanthipeptide cyclase MfuC in a cascaded way. Unprecedentedly, we biochemically characterized the first M61 family aminopeptidase MfuP involved in RiPP biosynthesis, demonstrating that MfuP showed the activity of an endopeptidase activity. MfuP is leader-independent but strictly selective for the multibridge structure of myxococin A and responsible for unwrapping two rings via amide bond hydrolysis, yielding myxococin B. Furthermore, the X-ray crystal structure of MfuP and structural analysis, including active-site mutations, are reported. Finally, myxococins are evaluated to exhibit anti-inflammatory activity in lipopolysaccharide-induced macrophages without detectable cytotoxicity.

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.

Natural epidithiodiketopiperazine alkaloids as potential anticancer agents: Recent mechanisms of action, structural modification, and synthetic strategies

Cancer has become a grave health crisis that threatens the lives of millions of people worldwide. Because of the drawbacks of the available anticancer drugs, the development of novel and efficient anticancer agents should be encouraged. Epidithiodiketopiperazine (ETP) alkaloids with a 2,5-diketopiperazine (DKP) ring equipped with transannular disulfide or polysulfide bridges or S-methyl moieties constitute a special subclass of fungal natural products. Owing to their privileged sulfur units and intriguing architectural structures, ETP alkaloids exhibit excellent anticancer activities by regulating multiple cancer proteins/signaling pathways, including HIF-1, NF-κB, NOTCH, Wnt, and PI3K/AKT/mTOR, or by inducing cell-cycle arrest, apoptosis, and autophagy. Furthermore, a series of ETP alkaloid derivatives obtained via structural modification showed more potent anticancer activity than natural ETP alkaloids. To solve supply difficulties from natural resources, the total synthetic routes for several ETP alkaloids have been designed. In this review, we summarized several ETP alkaloids with anticancer properties with particular emphasis on their underlying mechanisms of action, structural modifications, and synthetic strategies, which will offer guidance to design and innovate potential anticancer drugs.

Genome Mining and Screening for Secondary Metabolite Production in the Endophytic Fungus Dactylonectria alcacerensis CT-6

Endophytic fungi are a treasure trove of natural products with great chemical diversity that is largely unexploited. As an alternative to the traditional bioactivity-guided screening approach, the genome-mining-based approach provides a new methodology for obtaining novel natural products from endophytes. In our study, the whole genome of an endophyte, Dactylonectria alcacerensis CT-6, was obtained for the first time. Genomic analysis indicated that D. alcacerensis CT-6 has one 61.8 Mb genome with a G+C content of 49.86%. Gene annotation was extensively carried out using various BLAST databases. Genome collinearity analysis revealed that D. alcacerensis CT-6 has high homology with three other strains of the Dactylonectria genus. AntiSMASH analysis displayed 45 secondary metabolite biosynthetic gene clusters (BGCs) in D. alcacerensis CT-6, and most of them were unknown and yet to be unveiled. Furthermore, only six known substances had been isolated from the fermented products of D. alcacerensis CT-6, suggesting that a great number of cryptic BGCs in D. alcacerensis CT-6 are silent and/or expressed at low levels under conventional conditions. Therefore, our study provides an important basis for further chemical study of D. alcacerensis CT-6 using the gene-mining strategy to awaken these cryptic BGCs for the production of bioactive secondary metabolites.

Metabolic profiling for the discovery of two rare fusidane-type heterodimers from the fungal endophyte Acremonium pilosum F47

In our process of studying fusidane-type antibiotics, metabolomics-guided chemical investigation on the endophytic Acremonium pilosum F47 led to the isolation of two unique heterodimers, acremonidiols B and C (1 and 2) consisting of a fusidane-type triterpenoid motif and a steroid unit. Four biosynthetically related known natural products including fusidic acid (FA, 3), as well as ergosterol derivatives (4-6) were also obtained. Their structures were determined by the analyses of ESI-HRMS and NMR data. Compounds 1 and 2, as hybrid molecules comprising the fusidane triterpenoid and steroid, are rare in nature. Compared with the clinically used antibiotic FA (3), new compounds 1 and 2 showed no obvious antibiotic activity, indicating the importance of free C-21 carboxyl group for antibacterial activity.

Aspergillus nidulans—Natural Metabolites Powerhouse: Structures, Biosynthesis, Bioactivities, and Biotechnological Potential

Nowadays, finding out new natural scaffolds of microbial origin increases at a higher rate than in the past decades and represents an auspicious route for reinvigorating the pool of compounds entering pharmaceutical industries. Fungi serve as a depository of fascinating, structurally unique metabolites with considerable therapeutic significance. Aspergillus genus represents one of the most prolific genera of filamentous fungi. Aspergillus nidulans Winter G. is a well-known and plentiful source of bioactive metabolites with abundant structural diversity, including terpenoids, benzophenones, sterols, alkaloids, xanthones, and polyketides, many of which display various bioactivities, such as cytotoxicity, antioxidant, anti-inflammatory, antiviral, and antimicrobial activities. The current work is targeted to survey the reported literature on A. nidulans, particularly its metabolites, biosynthesis, and bioactivities, in addition to recent reports on its biotechnological potential. From 1953 till November 2022, relying on the stated data, 206 metabolites were listed, with more than 100 references.

Alteration of gut microbiome and metabolome by Clostridium butyricum can repair the intestinal dysbiosis caused by antibiotics in mice

This study evaluated the repair effects of Clostridium butyricum (CBX 2021) on the antibiotic (ABX)-induced intestinal dysbiosis in mice by the multi-omics method. Results showed that ABX eliminated more than 90% of cecal bacteria and also exerted adverse effects on the intestinal structure and overall health in mice after 10 days of the treatment. Of interest, supplementing CBX 2021 in the mice for the next 10 days colonized more butyrate-producing bacteria and accelerated butyrate production compared with the mice by natural recovery. The reconstruction of intestinal microbiota efficiently promoted the improvement of the damaged gut morphology and physical barrier in the mice. In addition, CBX 2021 significantly reduced the content of disease-related metabolites and meanwhile promoted carbohydrate digestion and absorption in mice followed the microbiome alternation. In conclusion, CBX 2021 can repair the intestinal ecology of mice damaged by the antibiotics through reconstructing gut microbiota and optimizing metabolic functions.

Anti-multidrug-resistant Staphylococcus aureus and anti-dermatophyte activities of secondary metabolites of the endophytic fungus Penicillium brevicompactum ANT13 associated with the Algerian endemic plant Abies numidica

This study aims to identify and assess the antimicrobial activity of endophytic fungi found in the endemic plant Abies numidica. Among all isolates, the ANT13 isolate demonstrated significant antimicrobial activity in the preliminary screening, particularly Staphylococcus aureus ATCC 25923 and Candida albicans ATCC 1024, with inhibition zones of 22 and 21.5 mm, respectively. Based on its morphological and molecular features, this isolate was identified as Penicillium brevicompactum. The maximum activity was observed in the ethyl acetate extract, followed by the dichloromethane extract; however, the n-hexane extract exhibited no activity. The ethyl acetate extract demonstrated very significant activity against the five strains of multidrug-resistant Staphylococcus aureus used, with average zones of inhibition ranging from 21 to 26 mm, in contrast to more resistant Enterococcus faecalis ATCC 49452 and Bacillus cereus ATCC 10876. The ethyl acetate extract was also very active against dermatophytes, where the zones of inhibition for Candida albicans, Microsporum canis, Trichophyton mentagrophytes, Trichophyton rubrum, and Epidermophyton floccosum were 23.5, 31, 43, 47, and 53.5 mm, respectively. The MIC values for dermatophytes ranged between 100 and 3200 µg/mL. The wild isolate of Penicillium brevicompactum ANT13 discovered as an endophyte in Abies numidica may be a distinctive source of novel compounds and drug discovery to trait dermatophytes and multidrug-resistant Staphylococcus aureus infections.

Deciphering the antimicrobial activity of multifaceted rhizospheric biocontrol agents of solanaceous crops viz., Trichoderma harzianum MC2, and Trichoderma harzianum NBG

The Solanaceae family is generally known to be the third most economically important plant taxon, but also harbors a host of plant pathogens. Diseases like wilt and fruit rot of solanaceous crops cause huge yield losses in the field as well as in storage. In the present study, eight isolates of Trichoderma spp. were obtained from rhizospheric micro-flora of three solanaceous crops: tomato, brinjal, and chili plants, and were subsequently screened for pre-eminent biocontrol activity against three fungal (Fusarium oxysporum f. sp. lycopersicum, Colletotrichum gloeosporioides, and Rhizoctonia solani) and one bacterial (Ralstonia solanacearum) pathogen. Morphological, ITS, and tef1α marker-based molecular identification revealed eight isolates were different strains of Trichoderma. Seven isolates were distinguished as T. harzianum while one was identified as T. asperellum. In vitro antagonistic and biochemical assays indicated significant biocontrol activity governed by all eight isolates. Two fungal isolates, T. harzianum MC2 and T. harzianum NBG were further evaluated to decipher their best biological control activity. Preliminary insights into the secondary metabolic profile of both isolates were retrieved by liquid chromatography-mass spectrometry (LC-MS). Further, a field experiment was conducted with the isolates T. harzianum MC2 and T. harzianum NBG which successfully resulted in suppression of bacterial wilt disease in tomato. Which possibly confer biocontrol properties to the identified isolates. The efficacy of these two strains in suppressing bacterial wilt and promoting plant growth in the tomato crop was also tested in the field. The disease incidence was significantly reduced by 47.50% and yield incremented by 54.49% in plants treated in combination with both the bioagents. The results of scanning electron microscopy were also in consensus with the in planta results. The results altogether prove that T. harzianum MC2 and T. harzianum NBG are promising microbes for their prospective use in agricultural biopesticide formulations.

Functional Endophytes Regulating Plant Secondary Metabolism: Current Status, Prospects and Applications

Endophytes, which are widely found in host plants and have no harmful effects, are a vital biological resource. Plant endophytes promote plant growth and enhance plants' resistance to diseases, pests, and environmental stresses. In addition, they enhance the synthesis of important secondary metabolites in plants and improve the potential applicability of plants in agriculture, medicine, food, and horticulture. In this review, we summarize the recent progress in understanding the interaction between endophytes and plants and summarize the construction of synthetic microbial communities (SynComs) and metaomics analysis of the interaction between endophytes and plants. The application and development prospects of endophytes in agriculture, medicine, and other industries are also discussed to provide a reference for further study of the interaction between endophytes and plants and further development and utilization of endophytes.

Key insights into secondary metabolites from various Chaetomium species

Endophytic fungi have proved to be a major source of secondary metabolites, wherein the genus Chaetomium has emerged as a source of multifarious bioactive natural compounds belonging to diverse classes such as chaetoglobosins, epipolythiodioxopiperazines, azaphilones, xanthones, anthraquinone, chromones, depsidones, terpenoids, and steroids. The objective of this review is to encapsulate recent findings on various Chaetomium strains, such as C. globosum, C. cupreum, C. elatum, C. subspirale, C. olivaceum, C. indicum, and C. nigricolor known for production of beneficial secondary metabolites, with an insight into their origin and function. A thorough literature survey was conducted for obtaining Chaetomium-derived secondary metabolites, with a scope of future application into drug development efforts. More than 100 secondary metabolites, with various beneficial properties such as antitumor, cytotoxic, antimalarial, and enzyme inhibitory activities, were enlisted. We believe this review will enhance the understanding of beneficial effects conferred by various Chaetomium-derived secondary metabolites and emphasize their potential in serving novel drug development efforts. KEY POINTS: • Identified Chaetomium-derived metabolites with potential for drug development. • More than 100 beneficial metabolites are enlisted. • Benefits include anti-cancerous, antimalarial, and anti-enzymatic properties.

Cytotoxic secondary metabolites isolated from Penicillium sp. YT2019-3321, an endophytic fungus derived from Lonicera Japonica

Introduction

Endophytic fungi associated with medicinal plants have proven to possess a high potential to produce structurally diverse metabolites, some of which are valuable for medicinal applications. In this study, Penicillium sp. YT2019-3321, an endophytic fungus derived from traditional Chinese medicine Lonicera japonica, was chemically studied.

Methods

The chemical structures of the isolated compounds were established by a correlative interpretation of HRESIMS and NMR spectroscopic data. The optical resolution of (±)-1 by chiral HPLC yielded individual enantiomers (+)-1 and (-)-1, and their stereochemistry were solved by X-ray diffraction crystallography, respectively.

Results and discussion

Eight structurally diversified secondary metabolites, including two previously unreported polyketides, named (±)-chrysoalide B (1) and penicidone E (2), were isolated and identified from Penicillium sp. YT2019-3321. Compound 2 possessed the γ-pyridone nucleus, which is rarely found in natural products. Cytotoxic assay revealed that the new compound 2 demonstrated a dose-dependent cytotoxicity against the human pancreatic tumor cells PATU8988T with the IC₅₀ value of 11.4 μM. Further studies indicated that 2 significantly induced apoptosis of PATU8988T cell lines, characterized by the morphologies abnormity, the reduction of cell number, the upregulation of proportion of apoptotic cells, and the ratio of Bcl-2 to Bax. Our study demonstrates that fungal secondary metabolites may have important significance in the discovery of drug leads.

Ecological and Oceanographic Perspectives in Future Marine Fungal Taxonomy

Marine fungi are an ecological rather than a taxonomic group that has been widely researched. Significant progress has been made in documenting their phylogeny, biodiversity, ultrastructure, ecology, physiology, and capacity for degradation of lignocellulosic compounds. This review (concept paper) summarizes the current knowledge of marine fungal diversity and provides an integrated and comprehensive view of their ecological roles in the world's oceans. Novel terms for 'semi marine fungi' and 'marine fungi' are proposed based on the existence of fungi in various oceanic environments. The major maritime currents and upwelling that affect species diversity are discussed. This paper also forecasts under-explored regions with a greater diversity of marine taxa based on oceanic currents. The prospects for marine and semi-marine mycology are highlighted, notably, technological developments in culture-independent sequencing approaches for strengthening our present understanding of marine fungi's ecological roles.

Production of Lovastatin using Liquid Cheese Whey by Fusarium nectrioides (MH173849), an Endophytic Fungi Isolated from Euphorbia hirta

Lovastatin is a naturally produced 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase enzyme inhibitor- used for treating hypercholesterolemia. It was the first statin drug which was approved by the United States Food and Drug Administration (USFDA). In the current study, endophytic fungus Fusarium nectrioides (MH173849) isolated from Euphorbia hirta L. was used for the production of lovastatin. Four different culture media indicated as M1, M2, M3 and M4 were used for the initial production of lovastatin. Liquid cheese whey was used as nitrogen source. Growth morphology of fungi was investigated using Scanning Electron Microscopy analysis. Also, parameters like temperature, pH, inoculum size, incubation time, and RPM were optimized for the obtaining highest lovastatin production. Among the four media, M4 was found to produce the maximum concentration of lovastatin. Parameters such as temperature of 28°C, pH 6, RPM – 180 rpm and inoculum size of 5 x107 spores/mL were optimal for the production of lovastatin by F. nectrioides (MH173849).

Dendrobine biosynthesis in Dendrobium nobile in four different habitats is affected by the variations in the endophytic fungal community

Dendrobium nobile, an epiphytic plant, is a traditional medicinal herb with abundant endophytes. It is unclear whether the variation in the diversity and abundance of endophytes could stimulate the biosynthesis of medicinal compounds in the plant. In this study, we collected fresh stems of D. nobile from four habitats for investigating the fungal community structure, dendrobine content, and environment factors and their correlations. The results indicated no significant difference in endophytic fungal diversity among the habitats; however, different dominant or special endophytic genera were observed in the hosts from different habitats. The altitude was observed to be positively related to the dendrobine content, as the stems collected from the altitude of 692 m exhibited the highest level of dendrobine. Furthermore, the relative abundance of Toxicocladosporium was found to be positively correlated with the altitude and dendrobine content. The epiphytic matrix exhibited a significant negative correlation with the relative abundance of the endophytic fungus Gibberella but did not exhibit any significant correlation with the dendrobine content. The results indicated that the abundance of endophytes in D. nobile was affected by the altitude and epiphytic matrix and that high Toxicocladosporium abundance and high altitude were conducive to dendrobine production.

Penipentenone A and brefeldin A derivatives potently inhibit KRAS mutant cancer cells from an endophytic fungus Penicillium brefeldianum F4a

Kirsten rat sarcoma viral oncogene homolog (KRAS) mutation is one of the most important carcinogenic factors in many solid tumors, which leads to the poor prognosis and therapy resistance of cancer. In order to develop direct or indirect KRAS inhibitors, one unique asymmetric dicyclopentenone penipentenone A, three undescribed brefeldin A (BFA) derivatives, and five known BFA derivatives were discovered from the endophytic fungus Penicillium brefeldianum guided by LC-MS/MS and cytotoxic activities. Their structures were elucidated by optical rotation, mass spectrometry, and NMR spectroscopic data. The absolute configurations of four undescribed compounds were elucidated by comparison of the experimental and calculated ECD spectra. The antiproliferative activities of obtained compounds against three KRAS mutant tumor cell lines and two BFA derivative-sensitive cell lines were evaluated. Besides 4-epi-15-epi-brefeldin A, the other compounds showed significant inhibitory activities against those tumor cell lines with IC₅₀ values ranging from 0.82 to 18.87 μM. Intriguingly, penipentenone A selectively inhibited KRAS mutant cancer cells SW620 (KRAS^G12V) and ASPC-1 (KRAS^G12D). BFA and four derivatives showed potent cytotoxic activities against all selected tumor cell lines H358 (KRAS^G12C), SW620 (KRAS^G12V), ASPC-1 (KRAS^G12D), PC-3, and HepG-2. These findings will provide undescribed lead compounds for developing drugs that target KRAS mutations.

Pyranone Derivatives With Antitumor Activities, From the Endophytic Fungus Phoma sp. YN02-P-3

Two new pyranone derivatives phomapyrone A (2) and phomapyrone B (3), one new coumarin 11S, 13R-(+)-phomacumarin A (1), three known pyranones (4–6), together with three known amide alkaloids fuscoatramides A-C (7–9), as well as 9S, 11R-(+)-ascosalitoxin (10) were isolated from the endophytic fungus Phoma sp. YN02-P-3, which was isolated from the healthy leaf tissue of a Paulownia tree in Yunnan Province, China. Their structures were elucidated using extensive NMR spectroscopic and HRESIMS data and by comparing the information with literature data. In addition, all compounds were tested for their cytotoxicity activity against human tumor cell lines, and the results showed that new compounds 1-3 showed moderate inhibitory activity against the HL-60 cell line with IC₅₀ values of 31.02, 34.62, and 27.90 μM, respectively.

Biotransformation of Androstenedione by Filamentous Fungi Isolated from Cultural Heritage Sites in the State Tretyakov Gallery

Simple Summary

Microorganisms are able to grow on substrates of the most diverse nature. One of the most practical habitats, in terms of cultural heritage conservation, is fine art objects such as tempera or oil paintings on canvas. Since tempera paints are produced on the basis of egg yolk, which is one of the richest sources of cholesterol in nature (up to 2% of dry weight), and in the process of aging of tempera materials, changes in cholesterol do not affect the core structure of the steroid nucleus, the group of fungi that we have isolated are tempera painting destructors is seen as a promising object for screening for their possible steroid-transforming activities. In this regard, the purpose of our work was to determine the ability to transform pharmaceutically significant steroids with dominant fungi-destructors of tempera paintings, previously isolated in the State Tretyakov Gallery. Consequently, we have demonstrated for the first time that fungi-destructors of tempera paintings have steroid-transforming activity and are promising microorganisms for screening for biotechnologically significant transformations of steroids with further industrial use.

Abstract

The transformation of steroids by microorganisms is widely used in medical biotechnology. A huge group of filamentous fungi is one of the most promising taxa for screening new biocatalytic reactions in order to obtain pharmaceutically significant steroids. In this work, we screened 10 filamentous fungi-destructors of egg tempera for the ability to biotransform androst-4-en-3,17-dione (AD) during cultivation in a liquid nutrient medium or in a buffer solution. These taxonomically unrelated strains, belonging to the classes Eurotiomycetes, Dothideomycetes and Sordariomycetes, are dominant representatives of the microbiome from halls where works of tempera painting are stored in the State Tretyakov Gallery (STG, Moscow, Russia). Since the binder of tempera paints, egg yolk, contains about 2% cholesterol, these degrading fungi appear to be a promising group for screening for steroid converting activity. It turned out that all the studied fungi-destructors are able to transform AD. Some strains showed transformation efficiency close to the industrial strain Curvularia lunata RNCIM F-981. In total, 33 steroids formed during the transformation of AD were characterized, for 19 of them the structure was established by gas chromatography/mass spectrometry analysis. In this work, we have shown for the first time that fungi-destructors of tempera paintings can efficiently transform steroids.

Enhancing the Discovery of Bioactive Secondary Metabolites From Fungal Endophytes Using Chemical Elicitation and Variation of Fermentation Media

Endophytic microorganisms are an important source of bioactive secondary metabolites. In this study, fungal endophytes obtained from A*STAR’s Natural Product Library (NPL) and previously isolated from different habitats of Singapore were investigated for their diversity, antimicrobial, and cytotoxic activities. A total of 222 fungal strains were identified on the basis of sequence analysis of ITS region of the rDNA gene. The identified fungal strains belong to 59 genera distributed in 20 orders. Majority of the identified strains (99%; 219 strains) belong to the phylum Ascomycota, while two strains belonged to the phylum Basidiomycota, and only one strain was from Mucoromycota phylum. The most dominant genus was Colletotrichum accounting for 27% of all the identified strains. Chemical elicitation using 5-azacytidine and suberoylanilide hydroxamic acid (SAHA) and variation of fermentation media resulted in the discovery of more bioactive strains. Bioassay-guided isolation and structure elucidation of active constituents from three prioritized fungal strains: Lophiotrema sp. F6932, Muyocopron laterale F5912, and Colletotrichum tropicicola F10154, led to the isolation of a known compound; palmarumycin C₈ and five novel compounds; palmarumycin CP₃₀, muyocopronol A-C and tropicicolide. Tropicicolide displayed the strongest antifungal activity against Aspergillus fumigatus with an IC₅₀ value of 1.8 μg/ml but with a weaker activity against the Candida albicans presenting an IC₅₀ of 7.1 μg/ml. Palmarumycin C₈ revealed the best antiproliferative activity with IC₅₀ values of 1.1 and 2.1 μg/ml against MIA PaCa-2 and PANC-1 cells, respectively.

Xenoacremones D-H, Bioactive Tyrosine-decahydrofluorene Analogues from the Plant-Derived Fungus Xenoacremonium sinensis

Five novel tyrosine-decahydrofluorene analogues, xenoacremones D−H (1−5), each bearing a fused 6/5/6 tricarbocyclic core and a 13-membered para-cyclophane ring system, were isolated from the endophytic fungus Xenoacremonium sinensis. Compound 1 was a novel polyketide synthase−nonribosomal peptide synthetase (PKS−NRPS) tyrosine-decahydrofluorene hybrid containing a 6/5/6/6/5 ring system. Their structures were elucidated from comprehensive spectroscopic analysis and electronic circular dichroism (ECD) calculations. All compounds were evaluated for their inhibitory activities on LPS-induced NO production in macrophages and their cytotoxicities against the NB4 and U937 cell lines. Compounds 3 and 5 exhibited potent anti-inflammatory activities in vitro. Compounds 1 and 3−5 displayed significant antiproliferative activity against the tumor cell lines (IC50 < 20 µM).

Versisterol, a new endophytic steroid with 3CL protease inhibitory activity from Avicennia marina (Forssk.) Vierh

A new epoxy ergostane sterol, named versisterol, was isolated from Aspergillus versicolor, an endophytic fungus from Avicennia marina. The structure of the isolated compound was deduced by means of one- and two-dimensional NMR and high-resolution mass spectrometry. The absolute stereochemistry was elucidated by NOESY analysis, and experimental and calculated time-dependent density functional theory (TD-DFT) circular dichroism spectroscopy. Versisterol inhibited 3CL protease (3CL^pro) with an IC₅₀ value of 2.168 ± 0.09 μM. Binding affinities and molecular interactions of versisterol towards 3CL^pro were scrutinized and compared to lopinavir with the help of the combination of docking computations and molecular dynamics (MD) simulation. In silico calculations demonstrated a comparable binding affinity of versisterol with a docking score of -9.4 kcal mol^-1, and MM-GBSA binding energy over 200 ns MD simulation of -29.1 kcal mol^-1, with respect to lopinavir (-9.8 and -32.2 kcal mol^-1, respectively). These findings suggested that versisterol can be an auspicious prototype for developing new 3CL^pro drug candidates against COVID-19.

Biocontrol Activity of Aspergillus terreus ANU-301 against Two Distinct Plant Diseases, Tomato Fusarium Wilt and Potato Soft Rot

To screen antagonistic fungi against plant pathogens, dual culture assay (DCA) and culture filtrate assay (CFA) were performed with unknown soil-born fungi. Among the different fungi isolated and screened from the soil, fungal isolate ANU-301 successfully inhibited growth of different plant pathogenic fungi, Colletotrichum acutatum, Alternaria alternata, and Fusarium oxysporum, in DCA and CFA. Morphological characteristics and rDNA internal transcribed spacer sequence analysis identified ANU-301 as Aspergillus terreus. Inoculation of tomato plants with Fusarium oxysporum f. sp. lycopersici (FOL) induced severe wilting symptom; however, co-inoculation with ANU-301 significantly enhanced resistance of tomato plants against FOL. In addition, culture filtrate (CF) of ANU-301 not only showed bacterial growth inhibition activity against Dickeya chrysanthemi (Dc), but also demonstrated protective effect in potato tuber against soft rot disease. Gas chromatography-tandem mass spectrometry analysis of CF of ANU-301 identified 2,4-bis(1-methyl-1-phenylethyl)-phenol (MPP) as the most abundant compound. MPP inhibited growth of Dc, but not of FOL, in a dose-dependent manner, and protected potato tuber from the soft rot disease induced by Dc. In conclusion, Aspergillus terreus ANU-301 could be used and further tested as a potential biological control agent.

Exploring Verrucosidin Derivatives with Glucose-Uptake-Stimulatory Activity from Penicillium cellarum Using MS/MS-Based Molecular Networking

Under the guidance of LC-MS/MS-based molecular networking, seven new verrucosidin derivatives, penicicellarusins A-G (3–9), were isolated together with three known analogues from the fungus Penicillium cellarum. The structures of the new compounds were determined by a combination of NMR, mass and electronic circular dichroism spectral data analysis. The absolute configuration of penicyrone A (10) was corrected based on X-ray diffraction analyses. Bioactivity screening indicated that compounds 1, 2, and 4 showed much stronger promising hypoglycemic activity than the positive drug (rosiglitazone) in the range of 25–100 μM, which represents a potential new class of hypoglycemic agents. Preliminary structure-activity relationship analysis indicates that the formation of epoxy ring on C₆-C₇ in the structures is important for the glucose uptake-stimulating activity. The gene cluster for the biosynthesis of 1–12 is identified by sequencing the genome of P. cellarum and similarity analysis with the gene cluster of verrucosidins in P. polonicum.

Novel Antioxidants and α-Glycosidase and Protein Tyrosine Phosphatase 1B Inhibitors from an Endophytic Fungus Penicillium brefeldianum F4a

Oxidative stress plays a very important role in the progression of diabetes and its complications. A therapeutic agent that is both antidiabetic and antioxidant would be the preferred choice for the treatment of diabetes. The crude extract of the endophytic fungus Penicillium brefeldianum F4a has significant antioxidant and α-glycosidase and protein tyrosine phosphatase 1B (PTP1B) inhibition activities. Chemical investigation of P. brefeldianum F4a using an activity-guided isolation led to the discovery of three new compounds called peniorcinols A-C (1-3) along with six known compounds: penialidins A (4), penialidin F (5), myxotrichin C (6), riboflavin (7), indole-3-acetic acid (8), and 2-(4-hydroxy-2-methoxy-6-methylphenyl) acetic acid (9). Their chemical structures were established by their NMR and HRESIMS. The absolute configurations of 1 and 3 were determined by experimental and calculated electronic circular dichroism (ECD). Their antioxidant activities were evaluated by DPPH• and ABTS•+ scavenging assays. Compounds 1-6 and 8-9 showed moderate to strong free radical scavenging activities. Significantly, 4-6 exhibited more potent ABTS•+ scavenging activity than that of the positive control. Their α-glycosidase and PTP1B inhibition activities were tested. Among them, compound 3 showed α-glucosidase inhibition activity, and compounds 7 and 8 showed PTP1B inhibitory activity for the first time. It is worth noting that 3 and 8 displayed both antioxidant and α-glycosidase or PTP1B inhibition activities. These finding suggest that compounds 3 and 8 could be used as lead compounds to generate new potent drugs for the treatment of oxidative stress-related diabetes.

An Optimized and Efficient CRISPR/Cas9 System for the Endophytic Fungus Pestalotiopsis fici

Endophytic fungi are emerging as attractive producers of natural products with diverse bioactivities and novel structures. However, difficulties in the genetic manipulation of endophytic fungi limit the search of novel secondary metabolites. In this study, we improved the polyethylene glycol (PEG)-mediated protoplast transformation method by introducing the CRISPR/Cas9 system into endophytic fungus Pestalotiopsis fici. Using this approach, we performed genome editing such as site-specific gene insertion, dual-locus mutations, and long DNA fragment deletions in P. fici efficiently. The average efficiency for site-specific gene insertion and two-site gene editing was up to 48.0% and 44.4%, respectively. In addition, the genetic manipulation time with long DNA fragment (5-10 kb) deletion was greatly shortened to one week in comparison with traditional methods such as Agrobacterium tumefaciens-mediated transformation (ATMT). Taken together, the development of the CRISPR/Cas9 system in the endophytic fungus will accelerate the discovery of novel natural products and further biological study.