Endophytic Fungi: A Treasure Trove of Antifungal Metabolites

Emerging and reemerging fungal infections are very common in nosocomial and non-nosocomial settings in people having poor immunogenic profiles either due to hematopoietic stem cell transplants or are using immunomodulators to treat chronic inflammatory disease or autoimmune disorders, undergoing cancer therapy or suffering from an immune weakening disease like HIV. The refractory behavior of opportunistic fungi has necessitated the discovery of unconventional antifungals. The emergence of black fungus infection during COVID-19 also triggered the antifungal discovery program. Natural products are one of the alternative sources of antifungals. Endophytic fungi reside and co-evolve within their host plants and, therefore, offer a unique bioresource of novel chemical scaffolds with an array of bioactivities. Hence, immense possibilities exist that these unique chemical scaffolds expressed by the endophytic fungi may play a crucial role in overcoming the burgeoning antimicrobial resistance. These chemical scaffolds so expressed by these endophytic fungi comprise an array of chemical classes beginning from cyclic peptides, sesquiterpenoids, phenols, anthraquinones, coumarins, etc. In this study, endophytic fungi reported in the last six years (2018-2023) have been explored to document the antifungal entities they produce. Approximately 244 antifungal metabolites have been documented in this period by different groups of fungi existing as endophytes. Various aspects of these antifungal metabolites, such as antifungal potential and their chemical structures, have been presented. Yet another unique aspect of this review is the exploration of volatile antifungal compounds produced by these endophytic fungi. Further strategies like epigenetic modifications by chemical as well as biological methods and OSMAC to induce the silent gene clusters have also been presented to generate unprecedented bioactive compounds from these endophytic fungi.

Endophytic fungi: A future prospect for breast cancer therapeutics and drug development

Globally, breast cancer is a primary contributor to cancer-related fatalities and illnesses among women. Consequently, there is a pressing need for safe and effective treatments for breast cancer. Bioactive compounds from endophytic fungi that live in symbiosis with medicinal plants have garnered significant interest in pharmaceutical research due to their extensive chemical composition and prospective medicinal attributes. This review underscores the potentiality of fungal endophytes as a promising resource for the development of innovative anticancer agents specifically tailored for breast cancer therapy. The diversity of endophytic fungi residing in medicinal plants, success stories of key endophytic bioactive metabolites tested against breast cancer and the current progress with regards to in vivo studies and clinical trials on endophytic fungal metabolites in breast cancer research forms the underlying theme of this article. A thorough compilation of putative anticancer compounds sourced from endophytic fungi that have demonstrated therapeutic potential against breast cancer, spanning the period from 1990 to 2022, has been presented. This review article also outlines the latest trends in endophyte-based drug discovery, including the use of artificial intelligence, machine learning, multi-omics approaches, and high-throughput strategies. The challenges and future prospects associated with fungal endophytes as substitutive sources for developing anticancer drugs targeting breast cancer are also being highlighted.

Metataxonomic analysis of endophytic bacteria of blackberry (Rubus ulmifolius Schott) across tissues and environmental conditions

(1) Background: Endophytic bacteria represent an important component of plant wellness. They have been widely studied for their involvement in plant development and enhancement of stress tolerance. In this work, the endophytic communities of roots, stems, and leaves of blackberry (Rubus ulmifolius Schott) were studied in three different niches: natural, riverside, and human-impacted niches. (2) Results: The microbiome composition revealed that Sphingomonadaceae was the most abundant family in all samples, accounting for 9.4-45.8%. In contrast, other families seem to be linked to a specific tissue or niche. Families Microbacteriaceae and Hymenobacteraceae increased their presence in stem and leaf samples, while Burkholderiaceae abundance was important in riverside samples. Alpha and beta diversity analyses showed that root samples were the most diverse, and they gathered together in the same cluster, apart from the rest of the samples. (3) Conclusions: The analysis of the microbiome of R. ulmifolius plants revealed that the composition was essentially the same in different niches; the differences were primarily influenced by plant tissue factors with a core genome dominated by Sphingomonadaceae. Additionally, it was observed that R. ulmifolius can select its own microbiome, and this remains constant in all tissues evaluated regardless the niche of sampling.

Coastal natural products: a review applied to antimycobacterial activity

Despite the many advances in drug research, natural products are still being explored as a promising source for discovering new bioactive compounds to treat global diseases such as tuberculosis. However, there is a lack of studies and information about coastal natural products, which thrive in the transitional environment between two different ecosystems and produce unique secondary metabolites. Mangroves, estuaries, and mudflats make up areas for coastal species and have shown promising results in antituberculosis research, some of them are present in hotspot areas. This review focuses on research conducted in coastal environments and explores the reasons why these natural products tend to outperform non-coastal ones against the causative agent of tuberculosis, Mycobacterium tuberculosis.

Antimicrobial activity of spiculisporic acid isolated from endophytic fungus Aspergillus cejpii of Hedera helix against MRSA

The surge in multidrug-resistant pathogens worldwide has jeopardized the clinical efficiency of many current antibiotics. This problem steered many researchers in their quest to discover new effective antimicrobial agents from natural origins including plants or their residing endophytes. In this work, we aimed to identify the endophytic fungi derived from Hedera helix L. and investigate their potential antimicrobial activity. Bioguided fractionation approach was conducted to isolate the pure compounds from the most active fungal fraction. Out of a total of six different isolated endophytic fungal strains, only Aspergillus cejpii showed the highest activity against all tested microbial strains. The most active fraction was the dichloromethane/methanol fraction (DCM:MeOH), where it showed significant activity against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Serratia marcescens, Acinetobacter baumannii, Salmonella typhi, and three drug-resistant clinical isolate strains including Methicillin-resistant Staphylococcus aureus (MRSA, H1), Pseudomonas aeruginosa (PS 16), and Acinetobacter baumannii (ACT 322) using tetracyline and kanamycin as the control antibiotics. Bioguided fractionation of the active fraction led to the isolation of the γ-butenolide, spiculisporic acid. Structure elucidation was carried out using 1H and 13C-NMR spectroscopic analysis. The compound showed good antimicrobial activities with minimum inhibitory concentration (MIC) values ranging from 3.9 to 31.25 μg/mL against all tested strains. Gas chromatography coupled to mass spectrometry (GC-MS) profiling was also carried out to identify the metabolites in the microbial crude extract. In conclusion, endophytic fungi, Aspergillus cejpii, isolated from Hedera helix L. roots showed promising antimicrobial activity which merits further in-depth investigations for potential utilization as a source of new antibiotics in the future. It can also be considered as a novel source for spiculisporic acid.

Endophytic fungi as a potential source of anti-cancer drug

Endophytes are considered one of the major sources of bioactive compounds used in different aspects of health care including cancer treatment. When colonized, they either synthesize these bioactive compounds as a part of their secondary metabolite production or augment the host plant machinery in synthesising such bioactive compounds. Hence, the study of endophytes has drawn the attention of the scientific community in the last few decades. Among the endophytes, endophytic fungi constitute a major portion of endophytic microbiota. This review deals with a plethora of anti-cancer compounds derived from endophytic fungi, highlighting alkaloids, lignans, terpenes, polyketides, polyphenols, quinones, xanthenes, tetralones, peptides, and spirobisnaphthalenes. Further, this review emphasizes modern methodologies, particularly omics-based techniques, asymmetric dihydroxylation, and biotic elicitors, showcasing the dynamic and evolving landscape of research in this field and describing the potential of endophytic fungi as a source of anticancer drugs in the future.

Bioactive saponin profiling of endophytic fungi from Asparagus racemosus

Thirty-five distinct endophytic fungi were isolated from the roots of Asparagus racemosus. Five out of 35 isolates were found to be efficient saponins producers and they were identified as Aspergillus terreus (E.F-1), Aspergillus flavus (E.F-7), Penicillium sp. (E.F-12), Talaromyces pinophilus(S-26), and Aspergillus terreus (Y-2) based on 18 sr RNA sequencing. The crude extracts of endophytic fungi were screened using High-performance liquid chromatography (HPLC) for quantitative analysis of saponin. The crude extracts of endophytic fungi were also characterised using FT-IR spectroscopy and mass spectrometry. The IR spectra of all five endophytic fungi crude extracts revealed the presence of -OH,-CH Alkyl,-CH3,-C-O-C,-C=C,-C=O stretching, which indicated the presence of saponin. Eight types of saponins recognised by mass spectrometry were Cyclamine saponin, Aspoligonin A, Sarsapogenin, Asparacosin A, Schidigera saponinD5, Aspargoside A, Dioscin, and Protodioscin. Endophytic fungi extracts also exhibited antimicrobial activity and antioxidant activity.

Optimization and characterization of antileukemic L-asparaginase produced by Fusarium solani endophyte

L-asparaginase is an antileukemic enzyme that hydrolyzes L-asparagine into L-aspartic acid and ammonia, causing cell starvation and apoptosis in susceptible leukemic cell populations. Currently, L-asparaginase obtained from bacterial sources is constrained by several issues, including lesser productivity, stability, selectivity, and higher toxicity. The goal of this study is to provide fungal L-asparaginase with in-vitro effectiveness towards different human carcinomas. L-asparaginase from endophytic Fusarium solani (Gene Bank accession number MW209717) isolated from the roots of the medicinal plant Hedera helix L. was characterized and optimized experimentally for maximum L-asparaginase production in addition to evaluating its subsequent cytotoxicity towards acute monocytic leukemia and human skin fibroblast cell lines. The enzyme production was maximized using potato dextrose media (15.44 IU/ml/hr) at the 5th and 6th days of fermentation with incubation temperature 30 °C, 3% asparagine, 150-180 rpm agitation rate and a 250 ml flask. Enzyme characterization studies revealed that the enzyme maintained its thermal stability with temperatures up to 60 °C. However, its optimal activity was achieved at 35 °C. On measuring the enzymatic activity at various temperatures and different pH, maximum enzyme activity was recorded at 40 °C and pH 8 using 0.1 M asparagine concentration. Results also revealed promising cytotoxic activity against acute monocytic leukemia with IC50 = 3.66 µg/ml and low cytotoxicity against tested normal human skin fibroblast cell line which suggested that it might have selective toxicity, and consequently it could be used as a less toxic alternative to the current formulations.

Metabolomic profiling and cytotoxic potential of three endophytic fungi of the genera Aspergillus, Penicillium and Fusarium isolated from Nigella sativa seeds assisted with docking studies

The main aim of our study is to investigate the anticancer potential of our cultivated entophytic fungal strains from Nigella sativa seeds. The strains were identified by sequencing of the partial 18S rRNA gene and the internal transcribed spacer (ITS) region as Aspergillus sp. (SA4), Penicillium sp. (SA5), and Fusarium sp. (SA6). We carried out metabolic profiling for three fungal strains to investigate their metabolites diversity. Profiling of the different extracts revealed their richness in diverse metabolites and consequently fourteen compounds (1-14) were annotated. In addition, the obtained extracts were examined against three cell lines HepG2, MCF-7 and Caco-2 showed activity with IC50 values in the range of 1.95-39.7 μg/mL. Finally, molecular docking study was performed showing questinol as the lowest glide binding score value (-5.925 kcal/mol) among all identified compounds. Our results showed Nigella sativa-associated endophytes as a promising source for further studies to look for anticancer secondary metabolites.

Four Undescribed Pyranones from the Scutellaria formosana-Derived Endophytic Fungi Ascomycota sp. FAE17

Four undescribed pyranone derivatives, named ascomycopyrones A-D (1-4), as well as one known analogue simplicilopyrone (5) (this is the first study to report the absolute configuration), were isolated from the endophytic fungus Ascomycota sp. FAE17 derived from the flowers of Scutellaria formosa. The structures of these pyranones were identified by comprehensive spectroscopic and MS analyses, and the absolute configurations were determined by their experimental and quantum chemical electronic circular dichroism (ECD) calculations. All isolated compounds were tested for various bioactivities, including antibacterial, cytotoxic activity, and NO inhibitory activity. Unfortunately, none of the compounds showed significant bioactivities.

The endophytic Fusarium strains: a treasure trove of natural products

The complexity and structural diversity of the secondary metabolites produced by endophytes make them an attractive source of natural products with novel structures that can help in treating life-changing diseases. The genus Fusarium is one of the most abundant endophytic fungal genera, comprising about 70 species characterized by extraordinary discrepancy in terms of genetics and ability to grow on a wide range of substrates, affecting not only their biology and interaction with their surrounding organisms, but also their secondary metabolism. Members of the genus Fusarium are a source of secondary metabolites with structural and chemical diversity and reported to exhibit diverse pharmacological activities. This comprehensive review focuses on the secondary metabolites isolated from different endophytic Fusarium species along with their various biological activities, reported in the period from April 1999 to April 2022.

Biological Control Potential of Endophytic Fungi with Amelioration of Systemic Resistance in Sunflower and GC-MS Metabolic Profiling of Talaromyces assiutensis

Endophytic fungi live inside plant tissues but do not cause any disease. Several reports have now revealed that they have great influence on host. In this study, the beneficial role of endophytic fungi is highlighted and explored. Endophytic fungi isolated from healthy plants were identified as Aspergillus terreus, Curvularia lunata, C. hawaiiensis, Macrophomina phaseolina, Fusarium solani, Talaromyces assiutensis, and T. trachyspermus using 18S rRNA gene sequencing. In vitro, fungi evaluated for antimicrobial activity, showed significant activity. These fungi were tested in field application by exploring their broad spectrum. Talaromyces assiutensis and T. trachyspermus were applied in pots and field plot experiments using sunflower as test plants, along with endophytic Cephalosporium sp., and Chaetomium sp. Endophytic fungi showed significant activity against root rot pathogens affecting sunflower and improved plant biomass. They also improved production of plant defense biochemical markers (polyphenolic content and salicylic acid) with improvement in antioxidant potential. These fungi are used as biological control agents, so their culture filtrates are used to check the presence of metabolites by GC-MS. Several new compounds were isolated from T. assiutensis. The major bioactive compounds are Coumarin, 3,4-dihydro-6-methoxy-4,4-dimethyl, 1-Monolinoleoylglycerol trimethylsilyl ether, 1,2-Propanediol, 3-(octadecyloxy), Ethyl iso-allocholate, and 1H-Pyrazole, which possess antioxidant, antitumor, antibacterial, anticancer, and antimicrobial properties. These findings will lead to further in-depth research toward the potential use of these endophytic fungi for their possible use in agriculture and drug formation.

The Endophytic Fungi Diversity, Community Structure, and Ecological Function Prediction of Sophora alopecuroides in Ningxia, China

Sophora alopecuroides L. has great medicinal and ecological value in northwestern China. The host and its microbiota are mutually symbiotic, collectively forming a holobiont, conferring beneficial effects to the plant. However, the analysis of diversity, mycobiota composition, and the ecological function of endophytic fungi in the holobiont of S. alopecuroides is relatively lacking. In this article, the fungal community profiling of roots, stems, leaves, and seeds of S. alopecuroides (at the fruit maturity stage) from Huamachi and Baofeng in Ningxia, China were investigated based on the ITS1 region, using high-throughput sequencing technology. As a result, a total of 751 operational taxonomic units (OTUs) were obtained and further classified into 9 phyla, 27 classes, 66 orders, 141 families, 245 genera, and 340 species. The roots had the highest fungal richness and diversity, while the stems had the highest evenness and pedigree diversity. There also was a significant difference in the richness of the endophytic fungal community between root and seed (p < 0.05). The organ was the main factor affecting the community structure of endophytic fungi in S. alopecuroides. The genera of unclassified Ascomycota, Tricholoma, Apiotrichum, Alternaria, and Aspergillus made up the vast majority of relative abundance, which were common in all four organs as well. The dominant and endemic genera and biomarkers of endophytic fungi in four organs of S. alopecuroides were different and exhibited organ specificity or tissue preference. The endophytic fungi of S. alopecuroides were mainly divided into 15 ecological function groups, among which saprotroph was absolutely dominant, followed by mixotrophic and pathotroph, and the symbiotroph was the least. With this study, we revealed the diversity and community structure and predicted the ecological function of the endophytic fungi of S. alopecuroides, which provided a theoretical reference for the further development and utilization of the endophytic fungi resources of S. alopecuroides.

Endophytes: Improving Plant Performance

Endophytes represent microorganisms that reside within plant tissues, without typically causing adverse effects to the plants, for a substantial part of their life cycle, and are primarily known for their beneficial role to their host plant [...].

Microbial Metabolites Beneficial to Plant Hosts Across Ecosystems

Plants are intimately connected with their associated microorganisms. Chemical interactions via natural products between plants and their microbial symbionts form an important aspect in host health and development, both in aquatic and terrestrial ecosystems. These interactions range from negative to beneficial for microbial symbionts as well as their hosts. Symbiotic microbes synchronize their metabolism with their hosts, thus suggesting a possible coevolution among them. Metabolites, synthesized from plants and microbes due to their association and coaction, supplement the already present metabolites, thus promoting plant growth, maintaining physiological status, and countering various biotic and abiotic stress factors. However, environmental changes, such as pollution and temperature variations, as well as anthropogenic-induced monoculture settings, have a significant influence on plant-associated microbial community and its interaction with the host. In this review, we put the prominent microbial metabolites participating in plant-microbe interactions in the natural terrestrial and aquatic ecosystems in a single perspective and have discussed commonalities and differences in these interactions for adaptation to surrounding environment and how environmental changes can alter the same. We also present the status and further possibilities of employing chemical interactions for environment remediation. Our review thus underlines the importance of ecosystem-driven functional adaptations of plant-microbe interactions in natural and anthropogenically influenced ecosystems and their possible applications.

In Vitro Phytobiological Investigation of Bioactive Secondary Metabolites from the Malus domestica-Derived Endophytic Fungus Aspergillus tubingensis Strain AN103

Endophytic fungi including black aspergilli have the potential to synthesize multiple bioactive secondary metabolites. Therefore, the search for active metabolites from endophytic fungi against pathogenic microbes has become a necessity for alternative and promising strategies. In this study, 25 endophytic fungal isolates associated with Malus domestica were isolated, grown, and fermented on a solid rice medium. Subsequently, their ethyl acetate crude extracts were pretested for biological activity. One endophytic fungal isolate demonstrated the highest activity and was chosen for further investigation. Based on its phenotypic, ITS ribosomal gene sequences, and phylogenetic characterization, this isolate was identified as Aspergillus tubingensis strain AN103 with the accession number (KR184138). Chemical investigations of its fermented cultures yielded four compounds: Pyranonigrin A (1), Fonsecin (2), TMC 256 A1 (3), and Asperazine (4). Furthermore, 1H-NMR, HPLC, and LC-MS were performed for the identification and structure elucidation of these metabolites. The isolated pure compounds showed moderate-to-potent antibacterial activities against Pseudomonas aeruginosa and Escherichia coli (MIC value ranged from 31 and 121 to 14.5 and 58.3 μg/mL), respectively; in addition, the time−kill kinetics for the highly sensitive bacteria against isolated compounds was also investigated. The antifungal activity results show that (3) and (4) had the maximum effect against Fusarium solani and A. niger with inhibition zones of 16.40 ± 0.55 and 16.20 ± 0.20 mm, respectively, and (2) had the best effect against Candida albicans, with an inhibition zone of 17.8 ± 1.35 mm. Moreover, in a cytotoxicity assay against mouse lymphoma cell line L5178Y, (4) exhibited moderate cytotoxicity (49% inhibition), whereas (1−3) reported weak cytotoxicity (15, 26, and 19% inhibition), respectively. Our results reveal that these compounds might be useful to develop potential cytotoxic and antimicrobial drugs and an alternative source for various medical and pharmaceutical fields.

Endophytic Fungi as a Source of Antiviral Compounds - A Review

Endophytic fungi are a rich source of secondary metabolites. The interactions between endophytes and their hosts lead to the production of several bioactive substances grouped into different classes, each having a wide variety of effects against various pathogens. The metabolites obtained from these organisms include steroids, alkaloids, phenols, isocoumarins, xanthones, quinones, and terpenoids, among others. These substances are known to have antibiotic, antiparasitic, antifungal, and antiviral effects. This review summarizes secondary metabolites with antiviral effects produced by endophytic fungi and highlights the importance of research in developing novel antiviral substances. We demonstrate that endophytic fungi are a rich source of secondary metabolites that combat pathologies caused by viruses. Optimizing practical and biotechnological screening tools for the research of these metabolites will provide promising drugs to combat these infections.

Diversity, Antimicrobial Activity, and Antibiotic Susceptibility Pattern of Endophytic Bacteria Sourced From Cordia dichotoma L

Endophytic bacteria isolated from medicinal plants are crucial for the production of antimicrobial agents since they are capable of possessing bioactive compounds with diverse structures and activities. Cordia dichotoma, a plant of medicinal importance native to the Jammu region of India, was selected for the isolation and characterization of culturable endophytic bacteria and evaluation of their antimicrobial activities. Standardized surface sterilization methods were employed to isolate thirty-three phenotypically distinguishable endophytic bacteria from the root, stem, and leaf parts of the plant. Shannon Wiener diversity index clearly divulged diverse endophytes in roots (0.85), stem (0.61), and leaf (0.54) tissues. Physio-biochemical features of the isolates differentiated the distinct variations in their carbohydrate utilization profile and NaCl tolerance. The endophytes produced an array of enzymes, namely, catalase, oxidase, amylase, cellulase, nitrate reductase, and lipase. The bacterial isolates belong to the genera Bacillus, Pseudomonas, Paenibacillus, Acidomonas, Streptococcus, Ralstonia, Micrococcus, Staphylococcus, and Alcalignes predominantly. However, the antibiotic susceptibility pattern indicated that the isolates were mostly sensitive to erythromycin and streptomycin, while they were resistant to rifampicin, amoxicillin, and bacitracin. Interestingly, majority of the bacterial endophytes of C. dichotoma showed antimicrobial activity against Bacillus subtilis followed by Klebsiella pneumoniae. The 16S rRNA sequence of Bacillus thuringiensis has been deposited in the NCBI GenBank database under accession number OM320575. The major compounds of the crude extract derived from endophytic B. thuringiensis OM320575, according to the metabolic profile examination by GC-MS, are dibutyl phthalate, eicosane, tetrapentacontane, heneicosane, and hexadecane, which possessed antibacterial activities. In conclusion, results indicated the potential of C. dichotoma to host a plethora of bacterial endophytes that produce therapeutic bioactive metabolites.

Production, Bioprocessing and Anti-Proliferative Activity of Camptothecin from Penicillium chrysogenum, "An Endozoic of Marine Sponge, Cliona sp.", as a Metabolically Stable Camptothecin Producing Isolate

Exploring the metabolic potency of fungi as camptothecin producers raises the hope of their usage as an industrial source of camptothecin, due to their short-life span and the feasibility of metabolic engineering. However, the tiny yield and loss of camptothecin productivity of fungi during storage and sub-culturing are challenges that counteract this approach. Marine fungi could be a novel source for camptothecin production, with higher yield and reliable metabolic sustainability. The marine fungal isolate Penicillium chrysogenum EFBL # OL597937.1 derived from the sponge "Cliona sp." has been morphologically identified and molecularly confirmed, based on the Internal Transcribed Spacer sequence, exhibiting the highest yield of camptothecin (110 μg/L). The molecular structure and chemical identity of P. chrysogenum derived camptothecin has been resolved by HPLC, FTIR and LC-MS/MS analyses, giving the same spectroscopic profiles and mass fragmentation patterns as authentic camptothecin. The extracted camptothecin displayed a strong anti-proliferative activity towards HEP-2 and HCT-116 (IC₅₀ values 0.33-0.35 µM). The yield of camptothecin was maximized by nutritional optimization of P. chrysogenum with a Plackett-Burman design, and the productivity of camptothecin increased by 1.8 fold (200 µg/L), compared to control fungal cultures. Upon storage at 4 °C as slope culture for 8 months, the productivity of camptothecin for P. chrysogenum was reduced by 40% compared to the initial culture. Visual fading of the mycelial pigmentation of P. chrysogenum was observed during fungal storage, matched with loss of camptothecin productivity. Methylene chloride extracts of Cliona sp. had the potency to completely restore the camptothecin productivity of P. chrysogenum, ensuring the partial dependence of the expression of the camptothecin biosynthetic machinery of P. chrysogenum on the chemical signals derived from the sponge, or the associated microbial flora. This is the first report describing the feasibility of P. chrysogenum, endozoic of Cliona sp., for camptothecin production, along with reliable metabolic biosynthetic stability, which could be a new platform for scaling-up camptothecin production.

Total synthesis and stereochemical assignment of bipolamide A acetate

Asymmetric total synthesis of an acetate analogue of the endophytic unstable secondary metabolite bipolamide A has been achieved for the first time adopting a convergent approach. The key feature of this synthesis includes Evans's asymmetric ethylation, Wittig olefination, Takai olefination, stereoselective Grignard addition and intermolecular Heck coupling. This eventually developed a synthetic route of the rarely found branched amine bearing an acyloin moiety. Our synthesis finally established unambiguously the stereochemistry of the unassigned C-8 center of the naturally occurring unstable bipolamide A.

Endophytic fungi of Brunfelsia uniflora: isolation, cryopreservation, and determination of enzymatic and antioxidant activity

Brunfelsia uniflora (Pohl.) D. Don (Solanaceae), commonly known as manacá-de-cheiro, is widely distributed in Brazil and used by local indigenous peoples as an antirheumatic, antisyphilitic, depurative, emetic, vermifuge, and purgative agent. Several studies have examined the biological activities and phytochemical profile of Brunfelsia; however, few have focused on the diversity of endophytic microorganisms that colonize members of the genus. This study aimed to isolate and cryopreserve endophytic fungi from B. uniflora and determine their cellulase, laccase, and antioxidant activities. Endophytic fungi were isolated from B. uniflora stems, cultured on wheat grains, immersed in a 150 g L^-1 aqueous sucrose solution, and cryopreserved at - 80 °C for 1 and 6 months. Cellulase activity was determined by a qualitative test using carboxymethylcellulose medium and laccase activity by a quantitative test based on the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate). Prior to antioxidant activity assays, fungi were grown in malt extract broth for production of mycelial biomass. A methanolic extract was prepared for evaluation of DPPH· scavenging activity, FRAP activity, and total phenolic content. A total of 46 endophytic fungal isolates were obtained from B. uniflora stems and classified into 24 groups according to morphological similarities. B. uniflora was shown to harbor different genera of ascomycete fungi as endophytic organisms. Mycelial viability was observed after 1 and 6 months of cryopreservation at - 80 °C. Fungi exhibited cellulase and laccase activities. Isolate CE23 had the highest laccase activity after 7 days of cultivation. Twelve isolates were found to have low total phenolic contents and DPPH· and FRAP activities.

Predicting global numbers of teleomorphic ascomycetes

Sexual reproduction is the basic way to form high genetic diversity and it is beneficial in evolution and speciation of fungi. The global diversity of teleomorphic species in Ascomycota has not been estimated. This paper estimates the species number for sexual ascomycetes based on five different estimation approaches, viz. by numbers of described fungi, by fungus:substrate ratio, by ecological distribution, by meta-DNA barcoding or culture-independent studies and by previous estimates of species in Ascomycota. The assumptions were made with the currently most accepted, “2.2–3.8 million” species estimate and results of previous studies concluding that 90% of the described ascomycetes reproduce sexually. The Catalogue of Life, Species Fungorum and published research were used for data procurement. The average value of teleomorphic species in Ascomycota from all methods is 1.86 million, ranging from 1.37 to 2.56 million. However, only around 83,000 teleomorphic species have been described in Ascomycota and deposited in data repositories. The ratio between described teleomorphic ascomycetes to predicted teleomorphic ascomycetes is 1:22. Therefore, where are the undiscovered teleomorphic ascomycetes? The undescribed species are no doubt to be found in biodiversity hot spots, poorly-studied areas and species complexes. Other poorly studied niches include extremophiles, lichenicolous fungi, human pathogens, marine fungi, and fungicolous fungi. Undescribed species are present in unexamined collections in specimen repositories or incompletely described earlier species. Nomenclatural issues, such as the use of separate names for teleomorph and anamorphs, synonyms, conspecific names, illegitimate and invalid names also affect the number of described species. Interspecies introgression results in new species, while species numbers are reduced by extinctions.

The Endophytic Aspergillus Strains: A Bountiful Source of Natural Products

Fungi that invade plant inner tissues without inducing disease symptoms are known as fungal endophytes. They represent a promising and tremendous reservoir of natural products with valuable biological potentials for application in medicine, agriculture and industry. Among the numerous existing endophytic fungi, Aspergillus strains constitute one of the most prolific sources of secondary metabolites with diverse chemical classes and interesting biological activities. This review covers the literature of the year 2020, reporting the isolation of 202 compounds obtained from more than ten different endophytic Aspergillus species associated with different host plants. Analysis and interpretation of the collected data revealed that chemical investigation of endophytes belonging to the genus Aspergillus may greatly contribute in the discovery of potential drug leads. The isolated metabolites were chemically various and exhibited diverse biological activities such as antibacterial, anti-cancer, anti-plasmodial, anti-inflammatory, antioxidant, immunosuppressive and antifungal activities. Moreover, adoption of advanced technology in molecular biology together with modern chemical tools is anticipated to improve the discovery of new biopharmaceuticals from this valuable microbial world in the future.

Functional and morphological analysis of isolates of phylloplane and rhizoplane endophytic bacteria interacting in different cocoa production systems in the Amazon

Endophytic bacteria colonize different internal tissues of plants without damaging their cells. They can establish themselves in the same niche as other microorganisms and develop antagonistic activities against phytopathogens. There is little research on the functional and morphological characterization of these bacteria in production systems in the Amazon. Thus, the objective of this work was to functionally and morphologically characterize endophytic bacteria isolated from cocoa trees (Theobroma cacao L.) and evaluate their antagonistic potential against phytopathogens. A total of 197 endophytic bacteria isolates were obtained from leaves and roots of cocoa plants with different production systems and at different times of the year. The characterization of functional groups consisted of proteolytic, amylolytic and cellulolytic activity and ability to fix nitrogen and solubilize phosphate. Morphological diversity was evaluated mainly according to the following parameters: shape, color, size and elevation of the colony. Thirteen isolates of endophytic bacteria, selected by cluster analysis, were used to evaluate the antagonistic potential in paired trials against four species of phytopathogenic fungi. The largest amount of endophytic bacteria was isolated from the root (95.9%), in the dry season. The most expressive activities with regards to the enzyme index were amylolytic (71.9%), proteolytic (70.2%) and nitrogen fixing (38.6%), respectively. The similarity analysis formed two clusters with isolates CS R 2.4 and CS R 2.25 exhibiting 100% similarity. Five isolates displayed inhibitory activity against phytopathogenic fungi, most notably isolate TS R 2.19, which exhibited antagonistic activity against all fungi and mycelial growth inhibition rates between 25.7% and 50.7%. Understanding the interaction between endophytes in cocoa plants is important as a possible additional tool in biological control. Our studies are incipient and the first to be carried out in different cocoa production systems in the state of Pará, Brazil.

Plant-derived bioactive compounds produced by Streptomyces variabilis LCP18 associated with Litsea cubeba (Lour.) Pers as potential target to combat human pathogenic bacteria and human cancer cell lines

To date, endophytic actinomycetes have been well-documented as great producers of novel antibiotics and important pharmaceutical leads. The present study aimed to evaluate potent bioactivities of metabolites synthesized by the strain LCP18 residing in the Vietnamese medicinal plant Litsea cubeba (Lour.) Pers towards human pathogenic bacteria and human cancer cell lines. Endophytic actinomycete strain LCP18 showed considerable inhibition against seven bacterial pathogens and three human tumor cell lines and was identified as species Streptomyces variabilis. Strain S. variabilis LCP18 was phenotypically resistant to fosfomycin, trimethoprim-sulfamethoxazole, dalacin, cefoxitin, rifampicin, and fusidic acid and harbored the two antibiotic biosynthetic genes such as PKS-II and NRPS. Further purification and structural elucidation of metabolites from the LCP18 extract revealed five plant-derived bioactive compounds including isopcrunetin, genistein, daidzein, syringic acid, and daucosterol. Among those, isoprunetin, genistein, and daidzein exhibited antibacterial activity against Salmonella typhimurium ATCC 14,028 and methicillin-resistant Staphylococcus epidermidis ATCC 35,984 with the MIC values ranging from 16 to 128 µg/ml. These plant-derived compounds also exhibited cytotoxic effects against human lung cancer cell line A549 with IC50 values of less than 46 μM. These findings indicated that endophytic S. variabilis LCP18 can be an alternative producer of plant-derived compounds which significantly show potential applications in combating bacterial infections and inhibition against lung cancer cell lines.

Endophytic fungi: A treasure trove of novel anticancer compounds

Cancer is a multifactorial disease with a convoluted genesis and progression. The emergence of multidrug resistance to presently be offered drug and relapse is by far, the most critical concern to tackle this deteriorating disease. Henceforth, there is undeniably an inflated necessity for safe, promising, and less harmful new anticancer drugs. Natural compounds from various sources like plants, animals, and microorganisms have occupied a center stage in drug discovery due to their tremendous chemical diversity and potential as therapeutic agents. Endophytic microbes are symbiotically associated with plants and have been proven to produce novel or analogues of host bioactive metabolites exhibiting a variety of biological activities including anticancer activity. This review emphasizes on structurally diverse unprecedented anticancer natural compounds that have been reported exclusively from endophytic fungi from 2016 to 2020. It covers chemical nature of metabolites, its fungal source associated with terrestrial, as well as marine plants and anticancer activity based on their cytotoxicity profile against various cancer cell lines. Many of these fungal metabolites with promising anticancer activity can be used as lead molecules for in silico experiments and deserve special attention from scientists for further in vitro and clinical research.

Azaphilones from an Endophytic Penicillium sp. Prevent Neuronal Cell Death via Inhibition of MAPKs and Reduction of Bax/Bcl-2 Ratio

Fourteen azaphilone-type polyketides (1-14), including nine new ones (1-6 and 8-10), were isolated from cultures of Vitex rotundifolia-associated Penicillium sp. JVF17, and their structures were determined by spectroscopic analysis together with computational methods and chemical reactions. Neuroprotective effects of the isolated compounds were evaluated against glutamate-induced neurotoxicity. Treatment with compounds 3, 6, 7, and 11-14 increased cell viabilities of hippocampal neuronal cells damaged by glutamate, with compound 12 being the most potent. Compound 12 markedly decreased intracellular Ca²⁺ and nuclear condensation levels. Mechanistically, molecular markers of apoptosis induced by treatment with glutamate, i.e., phosphorylation of MAPKs and elevated Bax/Bcl-2 expression ratio, were significantly lowered by compound 12. The azaphilones with an isoquinoline core structure were more active than those with pyranoquinones, but N-substitution decreased the activity. This study, including the structure-activity relationship, indicates that the azaphilone scaffold is a promising lead toward the development of novel neuroprotective agents.

Influence of plants and environmental variables on the diversity of soil microbial communities in the Yellow River Delta Wetland, China

Microorganisms play an important role in the biogeochemical cycle and ecological function regulation of wetlands, have a major impact on global climate change and are critical for maintaining the health of the global ecosystem. In order to investigate the relationships among plants, environmental variables, and microbial communities in coastal wetlands in the Yellow River Delta, we selected soils growing plants such as Suaeda salsa, Tamarix chinensis, Phragmites australis, and cotton etc. The results show that there were differences in microbial diversity among areas with different vegetation cover and the microbial abundance in Phragmites australis and Tamarix chinensis areas was higher than that in mudflat, Suaeda glauca and cotton field, plants increased the diversity of soil microorganisms. The structure and diversity of soil microorganisms were significantly higher than that of endophytes. The Shannon index of soil bacteria was about 4-5.5, while that of endophytes was about 0-4. The soil bacteria were mainly Firmicutes, Proteobacteria, Bacteroidetes and Actinobacteria, accounting for more than 90.0% in all samples. The Mn⁴⁺, Fe³⁺ and hydrolytic nitrogen contents in the soil of vegetation covered areas was lower than that of the bare beach, the content of hydrolytic nitrogen in Phragmites australis area was generally higher, and the content of SO₄^2- and NO₂^- in the area was lowest near oil fields. Redundancy analysis shows that the explanatory rates of environmental factors at the phylum and genus levels were 89.70% and 86.80%, respectively, and K (23.40%), NO₂^- (11.80%), Mn⁴⁺ (9.80%) and Na (8.00%) were the main factors explaining the structural changes and composition of microbial flora at the phylum level. This study provides an ecological perspective for understanding the influence mechanism between wetland microbial diversity and wetland ecosystem function. It is helpful for us to understand the interactions among plants, environmental variables, and microbial communities in the coastal wetland of the Yellow River Delta, and has important guiding significance for the scientific research of soil environmental remediation in the degraded coastal wetland of the Yellow River Delta.

Antimicrobial Compounds Isolated from Endolichenic Fungi: A Review

A lichen is a symbiotic relationship between a fungus and a photosynthetic organism, which is algae or cyanobacteria. Endolichenic fungi are a group of microfungi that resides asymptomatically within the thalli of lichens. Endolichenic fungi can be recognized as luxuriant metabolic artists that produce propitious bioactive secondary metabolites. More than any other time, there is a worldwide search for new antibiotics due to the alarming increase in microbial resistance against the currently available therapeutics. Even though a few antimicrobial compounds have been isolated from endolichenic fungi, most of them have moderate activities, implying the need for further structural optimizations. Recognizing this timely need and the significance of endolichenic fungi as a promising source of antimicrobial compounds, the activity, sources and the structures of 31 antibacterial compounds, 58 antifungal compounds, two antiviral compounds and one antiplasmodial (antimalarial) compound are summarized in this review. In addition, an overview of the common scaffolds and structural features leading to the corresponding antimicrobial properties is provided as an aid for future studies. The current challenges and major drawbacks of research related to endolichenic fungi and the remedies for them have been suggested.

Diversity of Marine Macro-Algicolous Endophytic Fungi and Cytotoxic Potential of Biscogniauxia petrensis Metabolites Against Cancer Cell Lines

Hypersaline environments are known to support diverse fungal species from various orders. The production of secondary metabolites is one of the strategies that fungi adopt to thrive under such extreme environments, bringing up the stress tolerance response. Some such unique secondary metabolites also exhibit clinical significance. The increasing prevalence of drug resistance in cancer therapy demands further exploration of these novel bioactive compounds as cancer therapeutics. In the present study, a total of 31 endophytic fungi harboring inside red, green, and brown marine algae have been isolated and identified. The maximum likelihood analysis and diversity indices of fungal endophytes revealed the phylogenetic relationship and species richness. The genus Aspergillus was found to be the dominating fungus, followed by Cladosporium spp. All the isolated endophytic fungal extracts were tested for their cytotoxicity against HeLa and A431 cancer cell lines. Nine isolates were further analyzed for their cytotoxic activity from the culture filtrate and mycelia extract. Among these isolates, Biscogniauxia petrensis showed potential cytotoxicity with CC50 values of 18.04 and 24.85 μg/ml against HeLa and A431 cells, respectively. Furthermore, the media and solvent extraction optimization revealed the highest cytotoxic active compounds in ethyl acetate extract from the potato dextrose yeast extract broth medium. The compound-induced cell death via apoptosis was 50-60 and 45% when assayed using propidium iodide-live/dead and loss of mitochondrial membrane potential assay, respectively, in HeLa cells. Four bioactive fractions (bioassay-based) were obtained and analyzed using chromatography and spectroscopy. This study reports, for the first time, the cytotoxic activity of an endophytic fungal community that was isolated from marine macro-algae in the Rameswaram coastal region of Tamil Nadu, India. In addition, B. petrensis is a prominent apoptotic agent, which can be used in pharmaceutical applications as a therapeutic.

A plant endophyte Staphylococcus hominis strain MBL_AB63 produces a novel lantibiotic, homicorcin and a position one variant

Here we report a jute endophyte Staphylococcus hominis strain MBL_AB63 isolated from jute seeds which showed promising antimicrobial activity against Staphylococcus aureus SG511 when screening for antimicrobial substances. The whole genome sequence of this strain, annotated using BAGEL4 and antiSMASH 5.0 to predict the gene clusters for antimicrobial substances identified a novel antimicrobial peptide cluster that belongs to the class I lantibiotic group. The predicted lantibiotic (homicorcin) was found to be 82% similar to a reported peptide epicidin 280 having a difference of seven amino acids at several positions of the core peptide. Two distinct peaks obtained at close retention times from a RP-HPLC purified fraction have comparable antimicrobial activities and LC-MS revealed the molecular mass of these peaks to be 3046.5 and 3043.2 Da. The presence of an oxidoreductase (homO) similar to that of epicidin 280- associated eciO or epilancin 15X- associated elxO in the homicorcin gene cluster is predicted to be responsible for the reduction of the first dehydrated residue dehydroalanine (Dha) to 2-hydroxypropionate that causes an increase of 3 Da mass of homicorcin 1. Trypsin digestion of the core peptide and its variant followed by ESI-MS analysis suggests the presence of three ring structures, one in the N-terminal and other two interlocking rings at the C-terminal region that remain undigested. Homicorcin exerts bactericidal activity against susceptible cells by disrupting the integrity of the cytoplasmic membrane through pore formation as observed under FE-SEM.

Extracellular metabolites of endophytic fungi from Azadirachta indica inhibit multidrug-resistant bacteria and phytopathogens

Aim: To evaluate antimicrobial activity of extracellular metabolites (EMs) of endophytic fungal isolates (EFIs) from Azadirachta indica. Materials & methods: EFIs were identified by internal transcribed spacer (ITS) sequencing. Antimicrobial activity, and minimum inhibitor concentration (MIC) and minimum bactericidal concentration (MBC) were determined using agar diffusion and microdilution method, respectively. Results: Seventeen EFIs were isolated from different organs of A. indica. Eight of them were identified based on ITS sequencing. The EMs of EFIs inhibited the growth of six multidrug-resistant (MDR) bacterial superbugs and three phytopathogenic fungi. The MDR bacterial superbugs are resistant to six commercial antibiotics of different generations but susceptible to EMs of EFIs. The MIC (0.125-1.0 μg/μl), MBC (0.5-4.0 μg/μl) and minimum fungicidal concentration (1.0-4.0 μg/μl) of the EMs from EFIs are lower enough. Conclusion: The EMs of the EFIs have promising antimicrobial activity against MDR bacteria and phytopathogenic fungi.

Molecular Phylogeny of Endophytic Fungi from Rattan (Calamus castaneus Griff.) Spines and Their Antagonistic Activities against Plant Pathogenic Fungi

Calamus castaneus is a common rattan palm species in the tropical forests of Peninsular Malaysia and is noticeable by the yellow-based spines that cover the stems. This study aimed to determine the prevalence of fungal endophytes within C. castaneus spines and whether they inhibit the growth of fungal pathogens. Twenty-one genera with 40 species of fungal endophytes were isolated and identified from rattan palm spines. Based on molecular identification, the most common isolates recovered from the spines were Colletotrichum (n = 19) and Diaporthe spp. (n = 18), followed by Phyllosticta spp., Xylaria sp., Trichoderma spp., Helminthosporium spp., Penicillium spp., Fusarium spp., Neopestalotiopsis spp., Arthrinium sp., Cyphellophora sp., Cladosporium spp., Curvularia sp., Bionectria sp., and Acremonium spp. Non-sporulating fungi were also identified, namely Nemania primolutea, Pidoplitchkoviella terricola, Muyocopron laterale, Acrocalymma fici, Acrocalymma medicaginis, and Endomelanconiopsis endophytica. The isolation of these endophytes showed that the spines harbor endophytic fungi. Most of the fungal endophytes inhibited the growth of several plant pathogenic fungi, with 68% of the interactions resulting in mutual inhibition, producing a clear inhibition zone of <2 mm. Our findings demonstrate the potential of the fungal endophytes from C. castaneus spines as biocontrol agents.

Structure and cytotoxicity of trichothecenes produced by the potato-associated fungus Trichothecium crotocinigenum

Seven previously undescribed trichothecenes, named trichothecrotocins M-S (1-7), along with five known compounds, were isolated from rice cultures of the potato-associated fungus Trichothecium crotocinigenum. Their structures and absolute configurations were determined through spectroscopic methods, single-crystal X-ray diffraction, and quantum chemistry calculations on ECD. Compound 1 possesses a rare 6,11-epoxy moiety in the trichothecene family. Compound 6 exhibited strong cytotoxic activity against MCF-7 cancer cell lines with an IC₅₀ value of 2.34 ± 0.45 μM. It promoted apoptosis induction in MCF-7 cells. Moreover, cell cycle analysis showed cell cycle arrest caused by compound 6 at the G2/M phase which resulted to cell proliferation inhibition and pro-apoptotic activity. Further quantitative real-time PCR (qRT-PCR) analysis confirmed that the G2/M arrest was accompanied by upregulation of p21 and down regulation of cyclins B1 in 6-treated MCF-7 cells.

Biologically Significant and Recently Isolated Alkaloids from Endophytic Fungi

A selection of the established and recently characterized alkaloids from the exploration of plant- and some marine-associated endophytic fungi is reviewed, with reference to alkaloids of biological significance.

Endophytic Microbial Diversity: A New Hope for the Production of Novel Anti-tumor and Anti-HIV Agents as Future Therapeutics

Cancer is a collective name for a variety of diseases that can begin in virtually every organ or body tissue as abnormal cells develop uncontrollably and ten million new cancer cases are diagnosed all over the world at present. Whereas HIV is a virus that makes people susceptible to infection and contributes to the condition of acquired immune deficiency syndrome (AIDS). Almost 37 million people are currently diagnosed with HIV and 1 million people die every year, which is the worst-case scenario. Potential medicinal compounds have played a crucial role in the production of certain clinically beneficial novel anti-cancer and anti-HIV agents that are produced from natural sources especially from plants. These include Taxol, Vinblastine, Podophyllotoxin, Betulinic acid, Camptothecin, and Vincristine, etc. In the past decades, bioactive compounds were extracted directly from the plant sources which was more time consuming, led to low yield productivity, high cost, and bad impact on biodiversity. Endophytes, the microorganisms that reside inside the host plant by not causing any kind of harm to them and have potential applications in agriculture, medicine, pollution, and food industries. Therefore, by isolating and characterizing novel endophytes from medicinal plants and extracting their secondary metabolites to produce useful bioactive compounds can be beneficial for well-being and society as a future therapeutics. This approach is not harmful to biodiversity economical, timesaving, low cost, and can lead to the discovery of various industrial and commercially important novel anti-tumor and anti-HIV agents in the future. The Himalayas are home to several medicinal plants and the endophytic microbial biodiversity of the Himalayan region is also not much explored yet. However, the effect of compounds from these endophytes on anticancer and antiviral activity, especially anti-HIV has been largely unexplored. Hence, the present review is designed to the exploration of endophytic microbial diversity that can give rise to the discovery of various novel potential industrially valuable bioactive compounds that can lessen the rate of such type of pandemic diseases in the future by providing low-cost future therapeutics in future.

Pipecolisporin, a Novel Cyclic Peptide with Antimalarial and Antitrypanosome Activities from a Wheat Endophytic Nigrospora oryzae

A novel cyclic antimalarial and antitrypanosome hexapeptide, pipecolisporin (1), was isolated from cultures of Nigrospora oryzae CF-298113, a fungal endophyte isolated from roots of Triticum sp. collected in a traditional agricultural land of Montefrío, Granada, Spain. The structure of this compound, including its absolute configuration, was elucidated by HRMS, 1-D and 2-D NMR spectroscopy, and Marfey's analysis. This metabolite displayed interesting activity against Plasmodium falciparum and Trypanosoma cruzi, with IC50 values in the micromolar range, and no significant cytotoxicity against the human cancer cell lines A549, A2058, MCF7, MIA PaCa-2, and HepG2.

Identification and Antibacterial Characterization of Endophytic Fungi from Artemisia sieberi

Endophytic fungi serve as a reservoir for important secondary metabolites. The current study focused on the antibacterial properties of endophytic fungi isolated from Artemisia sieberi. Initially, six endophytic fungi were isolated and purified from the stem of A. sieberi. Endophytic fungi were identified by morphological characteristics, as well as by molecular identification using 18S rRNA gene sequencing method. All the six isolates were subjected to the preliminary screening for their antibacterial activity against nine important pathogenic bacteria using the disk-diffusion method. Crude extracts of the most active isolate were obtained using ethyl acetate. Antibacterial activity of the ethyl acetate extract was evaluated using well diffusion method on the selected isolate. The antibacterial efficiency of the selected isolate was evaluated by determining the Minimum Inhibitory Concentration (MIC). MIC values were in appreciable quantity against both Gram-positive and Gram-negative bacteria ranging from 3.125 to 6.25 µg/mL and 12.5 to 50 µg/mL, respectively. This result indicated that Gram-positive bacteria were more susceptible to the endophytic fungi extract. Moreover, the molecular identification results revealed that all the isolates belong to Ascomycota and represented Aspergillus and Penicillium genera and three species: A. oryzae (three isolates), A. niger (one isolate), and P. chrysogenum (two isolates). All six endophytic fungi were able to inhibit the growth of at least two of the tested bacteria. Among the isolated strains, isolate AS2, which identified as P. chrysogenum, exhibited the highest antibacterial activity against all nine tested bacteria and was higher than or equal to the positive control against most of the tested bacteria. Future studies are required to isolate and identify these bioactive substances, which can be considered as a potential source for the synthesis of new antibacterial drugs to treat infectious diseases.

Bioactive Metabolites from the Endophytic Fungus Aspergillus sp. SPH2

In the current study, an ethyl acetate extract from the endophytic fungus Aspergillus sp. SPH2 isolated from the stem parts of the endemic plant Bethencourtia palmensis was screened for its biocontrol properties against plant pathogens (Fusarium moniliforme, Alternaria alternata, and Botrytis cinerea), insect pests (Spodoptera littoralis, Myzus persicae, Rhopalosiphum padi), plant parasites (Meloidogyne javanica), and ticks (Hyalomma lusitanicum). SPH2 gave extracts with strong fungicidal and ixodicidal effects at different fermentation times. The bioguided isolation of these extracts gave compounds 1-3. Mellein (1) showed strong ixodicidal effects and was also fungicidal. This is the first report on the ixodicidal effects of 1. Neoaspergillic acid (2) showed potent antifungal effects. Compound 2 appeared during the exponential phase of the fungal growth while neohydroxyaspergillic acid (3) appeared during the stationary phase, suggesting that 2 is the biosynthetic precursor of 3. The mycotoxin ochratoxin A was not detected under the fermentation conditions used in this work. Therefore, SPH2 could be a potential biotechnological tool for the production of ixodicidal extracts rich in mellein.

The Endophytic Microbiome as a Hotspot of Synergistic Interactions, with Prospects of Plant Growth Promotion

The plant root is the primary site of interaction between plants and associated microorganisms and constitutes the main components of plant microbiomes that impact crop production. The endophytic bacteria in the root zone have an important role in plant growth promotion. Diverse microbial communities inhabit plant root tissues, and they directly or indirectly promote plant growth by inhibiting the growth of plant pathogens, producing various secondary metabolites. Mechanisms of plant growth promotion and response of root endophytic microorganisms for their survival and colonization in the host plants are the result of complex plant-microbe interactions. Endophytic microorganisms also assist the host to sustain different biotic and abiotic stresses. Better insights are emerging for the endophyte, such as host plant interactions due to advancements in 'omic' technologies, which facilitate the exploration of genes that are responsible for plant tissue colonization. Consequently, this is informative to envisage putative functions and metabolic processes crucial for endophytic adaptations. Detection of cell signaling molecules between host plants and identification of compounds synthesized by root endophytes are effective means for their utilization in the agriculture sector as biofertilizers. In addition, it is interesting that the endophytic microorganism colonization impacts the relative abundance of indigenous microbial communities and suppresses the deleterious microorganisms in plant tissues. Natural products released by endophytes act as biocontrol agents and inhibit pathogen growth. The symbiosis of endophytic bacteria and arbuscular mycorrhizal fungi (AMF) affects plant symbiotic signaling pathways and root colonization patterns and phytohormone synthesis. In this review, the potential of the root endophytic community, colonization, and role in the improvement of plant growth has been explained in the light of intricate plant-microbe interactions.

Metabolic extract of the endophytic fungus Flavodon flavus isolated from Justicia brandegeana in the control of Alicyclobacillus acidoterrestris in commercial orange juice

In this work, the antibacterial activity of a crude extract of the endophytic fungus Flavodon flavus (JB257), isolated from leaves of Justicia brandegeana, was evaluated against both the vegetative and sporulated forms of Alicyclobacillus acidoterrestris. The microdilution technique was performed in order to determine the antibacterial activity of the crude extract alone as well as in combination with the bacteriocin, nisin. The minimum inhibitory concentration (MIC) of the crude extract and nisin alone against A. acidoterrestris vegetative forms were 250 μg/mL and 31.5 μg/mL, respectively, while the minimum bactericidal concentrations (MBC) were 1000 μg/mL and 62.5 μg/mL,respectively. For A. acidoterrestris spores, treatment with the crude extract at a concentration of 500 μg/mL caused a 47% reduction in growth, while nisin at 62.5 μg/mL could reduce 100% of the growth. The in vitro evaluation of the crude extract combined with nisin against A. acidoterrestris by the Checkerboard method showed a synergistic interaction between the two compounds. In addition, greater selectivity towards bacterial cells over host cells, a human hepatocyte cell line, was achieved when the crude extract was combined with nisin, Using scanning electron microscopy, interferences in the cell membrane of A. acidoterrestris could be observed after treatment with the crude extract. The results presented in this study indicate that the crude extract of the endophyte F. flavus has biotechnological potential in the food industry, especially for the treatment of orange juices through the control of A. acidoterrestris.

Microbial Communities in Soils and Endosphere of Solanum tuberosum L. and their Response to Long-Term Fertilization

An understanding of how fertilization influences endophytes is crucial for sustainable agriculture, since the manipulation of the plant microbiome could affect plant fitness and productivity. This study was focused on the response of microbial communities in the soil and tubers to the regular application of manure (MF; 330 kg N/ha), sewage sludge (SF; 330 and SF3x; 990 kg N/ha), and chemical fertilizer (NPK; 330-90-300 kg N-P-K/ha). Unfertilized soil was used as a control (CF), and the experiment was set up at two distinct sites. All fertilization treatments significantly altered the prokaryotic and fungal communities in soil, whereas the influence of fertilization on the community of endophytes differed for each site. At the site with cambisol, prokaryotic and fungal endophytes were significantly shifted by MF and SF3 treatments. At the site with chernozem, neither the prokaryotic nor fungal endophytic communities were significantly associated with fertilization treatments. Fertilization significantly increased the relative abundance of the plant-beneficial bacteria Stenotrophomonas, Sphingomonas and the arbuscular mycorrhizal fungi. In tubers, the relative abundance of Fusarium was lower in MF-treated soil compared to CF. Although fertilization treatments clearly influenced the soil and endophytic community structure, we did not find any indication of human pathogens being transmitted into tubers via organic fertilizers.

Cooperation, Competition, and Specialized Metabolism in a Simplified Root Nodule Microbiome

Microbiomes associated with various plant structures often contain members with the potential to make specialized metabolites, e.g., molecules with antibacterial, antifungal, or siderophore activities. However, when and where microbes associated with plants produce specialized metabolites, and the potential role of these molecules in mediating intramicrobiome interactions, is not well understood. Root nodules of legume plants are organs devoted to hosting symbiotic bacteria that fix atmospheric nitrogen and have recently been shown to harbor a relatively simple accessory microbiome containing members with the ability to produce specialized metabolites in vitro On the basis of these observations, we sought to develop a model nodule microbiome system for evaluating specialized microbial metabolism in planta Starting with an inoculum derived from field-grown Medicago sativa nodules, serial passaging through gnotobiotic nodules yielded a simplified accessory community composed of four members: Brevibacillus brevis, Paenibacillus sp., Pantoea agglomerans, and Pseudomonas sp. Some members of this community exhibited clear cooperation in planta, while others were antagonistic and capable of disrupting cooperation between other partners. Using matrix-assisted laser desorption ionization-imaging mass spectrometry, we found that metabolites associated with individual taxa had unique distributions, indicating that some members of the nodule community were spatially segregated. Finally, we identified two families of molecules produced by B. brevisin planta as the antibacterial tyrocidines and a novel set of gramicidin-type molecules, which we term the britacidins. Collectively, these results indicate that in addition to nitrogen fixation, legume root nodules are likely also sites of active antimicrobial production.

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.

Exploiting the Biosynthetic Potency of Taxol from Fungal Endophytes of Conifers Plants; Genome Mining and Metabolic Manipulation

Endophytic fungi have been considered as a repertoire for bioactive secondary metabolites with potential application in medicine, agriculture and food industry. The biosynthetic pathways by fungal endophytes raise the argument of acquisition of these machineries of such complex metabolites from the plant host. Diterpenoids "Taxol" is the most effective anticancer drug with highest annual sale, since its discovery in 1970 from the Pacific yew tree, Taxus brevifolia. However, the lower yield of Taxol from this natural source (bark of T. brevifolia), availability and vulnerability of this plant to unpredicted fluctuation with the ecological and environmental conditions are the challenges. Endophytic fungi from Taxus spp. opened a new avenue for industrial Taxol production due to their fast growth, cost effectiveness, independence on climatic changes, feasibility of genetic manipulation. However, the anticipation of endophytic fungi for industrial Taxol production has been challenged by the loss of its productivity, due to the metabolic reprograming of cells, downregulating the expression of its encoding genes with subculturing and storage. Thus, the objectives of this review were to (1) Nominate the endophytic fungal isolates with the Taxol producing potency from Taxaceae and Podocarpaceae; (2) Emphasize the different approaches such as molecular manipulation, cultural optimization, co-cultivation for enhancing the Taxol productivities; (3) Accentuate the genome mining of the rate-limiting enzymes for rapid screening the Taxol biosynthetic machinery; (4) Triggering the silenced rate-limiting genes and transcriptional factors to activates the biosynthetic gene cluster of Taxol.

Recent advances in inducing endophytic fungal specialized metabolites using small molecule elicitors including epigenetic modifiers

Today when the quest of new lead molecules to supply the development pipeline is driving the course of drug discovery, endophytic fungi with their outstanding biosynthetic potential seem to be highly promising avenues for natural product scientists. However, challenges such as the production of inadequate quantities of compounds, the attenuation or loss of ability of endophytes to produce the compound of interest when grown in culture and the inability of fungal endophytes to express their full biosynthetic potential in laboratory conditions have been the major constraints. These have led to the application of small chemical elicitors that induce epigenetic changes in fungi to activate their silent gene clusters optimizing the amount of metabolites of interest or inducing the synthesis of hitherto undescribed compounds. In this respect small molecular weight compounds which are known to function as inhibitors of histone deacetylase (HDAC), DNA methyltransferase (DNMT) and proteasome have proven their efficacy in enhancing or inducing the production of specialized metabolites by fungi. Moreover, organic solvents, metals and plants extracts are also acknowledged for their ability to cause shifts in fungal metabolism. We highlight the successful studies from the past two decades reporting the ability of structurally diverse small molecular weight compounds to elicit the production of previously undescribed metabolites from endophytic fungi grown in culture. This mini review argues in favor of chemical elicitation as an effective strategy to optimize the production of fungal metabolites and invigorate the pipeline of drug discovery with new chemical entities.