Bioactive metabolites from Penicillium sp., an endophytic fungus residing in Hopea hainanensis

2,4-Quinolinedione alkaloids: occurrence and biological activities

Natural products are an important source of chemical scaffolds that have diverse biological activities. They can be used directly or as starting templates for the development of innovative pharmaceutical agents. Among natural products, quinoline alkaloids are one of the most extensively studied groups. 2,4-Quinolinedione (2,4-QD) alkaloids, which are found in a variety of natural sources, possess valuable biological properties. This review examines the natural occurrence and bioactivities of 2,4-QD alkaloids, which have not been studied in as much depth in previous research.

Genetic diversity assessment of Hopea hainanensis in Hainan Island

Hopea hainanensis (Dipterocarpaceae) is an endangered tree species restricted to Hainan Island, China, and a small part of Northern Vietnam. On Hainan Island, it is an important indicator species for tropical forests. The wood of Hopea hainanensis has a very high utilization value in nature since it is compact in structure, hard in texture, not easily deformed after drying, durable, and resistant to sunlight and water. As a result of its high quality, it has been felled and mined by humans without restraint, resulting in a reduction of its population size, severe habitat fragmentation, and a sharp decline in its population. Therefore, its conservation biology needs to be researched urgently. Researchers are currently focusing on the ecological factors and seed germination in the habitat of Hopea hainanensis to determine its endangered status. In the literature, there are no systematic analyses of the endangered mechanism of Hopea hainanensis in terms of genetic diversity. It focuses especially on the systematic genetic diversity of Hopea hainanensis in fragmented habitats. Using single nucleotide polymorphism (SNP) and genotyping-by-sequencing (GBS) technology, 42 samples from seven different cohabitation groups were genotyped. The results showed that the average heterozygosity of the six populations of Hopea hainanensis was 19.77%, which indicated that the genetic diversity of Hopea hainanensis was low. Genetic diversity research is essential for rare and endangered plant protection research. We can find a scientific basis for protecting endangered plants on slope bases by analyzing genetic differences and relationships among populations.

Chemical epigenetic modifiers enhance the production of immunosuppressants from the endophytic fungus Aspergillus fumigatus isolated from Cynodon dactylon

Chemical epigenetic modifiers applied on a plant endophytic fungus Aspergillus fumigatus isolated from a healthy stem of terrestrial plant Cynodon dactylon, significantly changed of metabolic profile and resulted in the isolation of nineteen compounds, including ten alkaloids (1-10), six polyketides (11-16), and three benzene derivatives (17-19). This is the first report of 14, 18 and 19 being isolated from this fungal species. And compound 14 was known as a synthetic product and isolated as a natural product for the first time. HPLC profiles of the control and treated samples indicated that compounds 11, 16, 18 are belonged to the newly induced secondary metabolites. Their structures were elucidated on the basis of extensive NMR spectroscopic and mass spectrometric analyses. The immunosuppressive and cytotoxic activities of all isolated compounds were evaluated.

Fungal Endophytes as Efficient Sources of Plant-Derived Bioactive Compounds and Their Prospective Applications in Natural Product Drug Discovery: Insights, Avenues, and Challenges

Fungal endophytes are well-established sources of biologically active natural compounds with many producing pharmacologically valuable specific plant-derived products. This review details typical plant-derived medicinal compounds of several classes, including alkaloids, coumarins, flavonoids, glycosides, lignans, phenylpropanoids, quinones, saponins, terpenoids, and xanthones that are produced by endophytic fungi. This review covers the studies carried out since the first report of taxol biosynthesis by endophytic Taxomyces andreanae in 1993 up to mid-2020. The article also highlights the prospects of endophyte-dependent biosynthesis of such plant-derived pharmacologically active compounds and the bottlenecks in the commercialization of this novel approach in the area of drug discovery. After recent updates in the field of 'omics' and 'one strain many compounds' (OSMAC) approach, fungal endophytes have emerged as strong unconventional source of such prized products.

Isolation and screening of stress-resistant endophytic fungus strains from wild and cultivated soybeans in cold region of China

In this study, we firstly reported the large-scale screening and isolation of endophytic fungi from nine wild and six cultivated soybeans in the cold regions of China. We totally isolated 302 endophytic fungal strains, of which 215 strains are isolated from the wild soybeans and 87 are identified from cultivated soybeans. Among these endophytic fungal strains, in the roots, stems, and leaves, 24.17% were isolated from roots, 28.8% were isolated from stems, and 47.01% were isolated from leaves, respectively. Most endophytic fungal strains isolated from the wild soybean roots were the species of Fusarium genus, and the fungal strains in the stems were the species of ascomycetes and Fusarium fungi, whereas most strains in the leaves were Alternaria fungi. To analyze the taxonomy of the obtained samples, we sequenced and compared their rDNA internal transcribed spacer (ITS) sequences. The data showed that 6 strains are putatively novel strains exhibiting ≤ 97% homology with the known strains. We next measured the secondary metabolites produced by the different strains and we found 11 strains exhibited high-performance synthesis of triterpenoids, phenols, and polysaccharides. Furthermore, we characterized their tolerance to abiotic stresses. The results indicated that 4 strains exhibited high tolerance to cadmium, and some strains exhibited resistance to acid, and alkali. The results of the study could facilitate the further exploration of the diversity of plant endophytic fungi and the potential applications of the fungi to practical agriculture and medicine industries. KEY POINTS: • 302 endophytic fungal strains isolated from wild soybean and cultivated soybean • 11 strains had high contents of triterpenoids, phenols, and polysaccharides • 4 strains exhibited high Cd tolerance, and a few strains with strong tolerance to acid and alkali solution.

Bioactive potential of endophytic fungus Chaetomium globosum and GC-MS analysis of its responsible components

The recent exploration of various medicinal plants for bioactive potential has led to the growing interest to explore their endophytes for such bioactive potential which may turn out to be better option than the plants. In the present study, Chaetomium globosum, an endophytic fungus isolated from Moringa oleifera Lam has been explored for its various biological activities. The chloroformic extract of C. globosum showed good antimutagenicity against the reactive carcinogenic mutagen, 2-aminofluorene (2-AF) in Ames test. The antiproliferative activity against various cell lines such as HCT-15, HeLa and U87-MG was found to be dose dependent and the viability reduced to 9.26%, 15.7% and 16.3%, respectively. Further, the chloroformic fungal extract was investigated for free radical scavenging activity using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethyl-benzthiazolin-6-sulfonic acid) assay which showed the IC₅₀ value of 45.16 µg/ml and 50.55 µg/ml, respectively. The fungal extract also showed good ferric reducing power. Total phenolic and flavonoid content was found to be in linear relationship with the antioxidant potential of the fungal extract. High performance liquid chromatography showed the presence of phenolics which may help to combat the free radicals. The presence of various bioactive compounds was analysed by GC–MS which endorsed Chaetomium globosum to be a promising candidate for drug development.

Biological Evaluation and In Silico Study of Benzoic Acid Derivatives from Bjerkandera adusta Targeting Proteostasis Network Modules

A main cellular functional module that becomes dysfunctional during aging is the proteostasis network. In the present study, we show that benzoic acid derivatives isolated from Bjerkandera adusta promote the activity of the two main protein degradation systems, namely the ubiquitin-proteasome (UPP) and especially the autophagy-lysosome pathway (ALP) in human foreskin fibroblasts. Our findings were further supported by in silico studies, where all compounds were found to be putative binders of both cathepsins B and L. Among them, compound 3 (3-chloro-4-methoxybenzoic acid) showed the most potent interaction with both enzymes, which justifies the strong activation of cathepsins B and L (467.3 ± 3.9%) on cell-based assays. Considering that the activity of both the UPP and ALP pathways decreases with aging, our results suggest that the hydroxybenzoic acid scaffold could be considered as a promising candidate for the development of novel modulators of the proteostasis network, and likely of anti-aging agents.

Endophytic Fungi-Alternative Sources of Cytotoxic Compounds: A Review

Cancer is a major cause of death worldwide, with an increasing number of cases being reported annually. The elevated rate of mortality necessitates a global challenge to explore newer sources of anticancer drugs. Recent advancements in cancer treatment involve the discovery and development of new and improved chemotherapeutics derived from natural or synthetic sources. Natural sources offer the potential of finding new structural classes with unique bioactivities for cancer therapy. Endophytic fungi represent a rich source of bioactive metabolites that can be manipulated to produce desirable novel analogs for chemotherapy. This review offers a current and integrative account of clinically used anticancer drugs such as taxol, podophyllotoxin, camptothecin, and vinca alkaloids in terms of their mechanism of action, isolation from endophytic fungi and their characterization, yield obtained, and fungal strain improvement strategies. It also covers recent literature on endophytic fungal metabolites from terrestrial, mangrove, and marine sources as potential anticancer agents and emphasizes the findings for cytotoxic bioactive compounds tested against specific cancer cell lines.

Determination and production of antimicrobial compounds by Aspergillus clavatonanicus strain MJ31, an endophytic fungus from Mirabilis jalapa L. using UPLC-ESI-MS/MS and TD-GC-MS analysis

Endophytic fungi associated with medicinal plants are reported as potent producers of diverse classes of secondary metabolites. In the present study, an endophytic fungi, Aspergillus clavatonanicus strain MJ31, exhibiting significant antimicrobial activity was isolated from roots of Mirabilis jalapa L., was identified by sequencing three nuclear genes i.e. internal transcribed spacers ribosomal RNA (ITS rRNA), 28S ribosomal RNA (28S rRNA) and translation elongation factor 1- alpha (EF 1α). Ethyl acetate extract of strain MJ31displayed significant antimicrobial potential against Bacillus subtilis, followed by Micrococccus luteus and Staphylococcus aureus with minimum inhibitory concentrations (MIC) of 0.078, 0.156 and 0.312 mg/ml respectively. In addition, the strain was evaluated for its ability to synthesize bioactive compounds by the amplification of polyketide synthase (PKS) and non ribosomal peptide synthetase (NRPS) genes. Further, seven antibiotics (miconazole, ketoconazole, fluconazole, ampicillin, streptomycin, chloramphenicol, and rifampicin) were detected and quantified using UPLC-ESI-MS/MS. Additionally, thermal desorption-gas chromatography mass spectrometry (TD-GC-MS) analysis of strain MJ31 showed the presence of 28 volatile compounds. This is the first report on A. clavatonanicus as an endophyte obtained from M. jalapa. We conclude that A. clavatonanicus strain MJ31 has prolific antimicrobial potential against both plant and human pathogens and can be exploited for the discovery of new antimicrobial compounds and could be an alternate source for the production of secondary metabolites.

Tricking Arthrinium malaysianum into Producing Industrially Important Enzymes Under 2-Deoxy D-Glucose Treatment

This study catalogs production of industrially important enzymes and changes in transcript expression caused by 2-deoxy D-glucose (2-DG) treatment in Arthrinium malaysianum cultures. Carbon Catabolite Repression (CCR) induced by 2-DG in this species is cAMP independent unlike many other organisms. Higher levels of secreted endoglucanase (EG), β-glucosidase (BGL), β-xylosidase (BXL), and filter paper activity assay (FPase) enzymes under 2-DG treatment can be exploited for commercial purposes. An integrated RNA sequencing and quantitative proteomic analysis was performed to investigate the cellular response to 2-DG in A. malaysianum. Analysis of RNASeq data under 2-DG treated and control condition reveals that 56% of the unigenes do not have any known similarity to proteins in non-redundant database. Gene Ontology IDs were assigned to 36% of the transcripts (13260) and about 5207 (14%) were mapped to Kyoto Encyclopedia of Genes and Genomes pathway (KEGG). About 1711 genes encoding 2691 transcripts were differentially expressed in treated vs. control samples. Out of the 2691 differentially expressed transcripts, only 582 have any known function. The most up regulated genes belonged to Pentose Phosphate Pathways and carbohydrate degradation class as expected. In addition, genes involved in protein folding, binding, catalytic activity, DNA repair, and secondary metabolites were up-regulated under 2-DG treatment. Whereas genes encoding glycosylation pathways, growth, nutrient reservoir activity was repressed. Gene ontology analysis of the differentially expressed genes indicates metabolic process (35%) is the pre-dominant class followed by carbohydrate degradation (11%), protein folding, and trafficking (6.2%) and transport (5.3%) classes. Unlike other organisms, conventional unfolded protein response (UPR) was not activated in either control or treated conditions. Major enzymes secreted by A. malaysianum are those degrading plant polysaccharides, the most dominant ones being β-glucosidase, as demonstrated by the 2D gel analysis. A set of 7 differentially expressed mRNAs were validated by qPCR. Transmission electron microscopy analyses demonstrated that the 2-DG treated cell walls of hyphae showed significant differences in the cell-wall thickness. Overall 2-DG treatment in A. malaysianum induced secretion of large amount of commercially viable enzymes compared to other known species.

Alkaloids Produced by Endophytic Fungi: A Review

In recent years, a number of alkaloids have been discovered from endophytic fungi in plants, which exhibited excellent biological properties such as antimicrobial, insecticidal, cytotoxic, and anticancer activities. This review mainly deals with the research progress on endophytic fungi for producing bioactive alkaloids such as quinoline and isoquinoline, amines and amides, indole derivatives, pyridines, and quinazolines. The biological activities and action mechanisms of these alkaloids from endophytic fungi are also introduced. Furthermore, the relationships between alkaloid-producing endophytes and their host plants, as well as their potential applications in the future are discussed.

Chemical and Functional Diversity of Natural Products from Plant Associated Endophytic Fungi

This review describes examples of naturally occurring bioactive compounds obtained from fungal endophytes from various host plants. The main topics addressed are sources, identification, biological activity, biosynthesis, and ecological and chemosystematic significance of those bioactive compounds whose sources were well defined.