Endophytic Fungi: A Source of Potential Antifungal Compounds

The limitless endophytes: their role as antifungal agents against top priority pathogens

Multi resistant fungi are on the rise, and our arsenal compounds are limited to few choices in the market such as polyenes, pyrimidine analogs, azoles, allylamines, and echinocandins. Although each of these drugs featured a unique mechanism, antifungal resistant strains did emerge and continued to arise against them worldwide. Moreover, the genetic variation between fungi and their host humans is small, which leads to significant challenges in new antifungal drug discovery. Endophytes are still an underexplored source of bioactive secondary metabolites. Many studies were conducted to isolate and screen endophytic pure compounds with efficacy against resistant yeasts and fungi; especially, Candida albicans, C. auris, Cryptococcus neoformans and Aspergillus fumigatus, which encouraged writing this review to critically analyze the chemical nature, potency, and fungal source of the isolated endophytic compounds as well as their novelty features and SAR when possible. Herein, we report a comprehensive list of around 320 assayed antifungal compounds against Candida albicans, C. auris, Cryptococcus neoformans and Aspergillus fumigatus in the period 1980-2024, the majority of which were isolated from fungi of orders Eurotiales and Hypocreales associated with terrestrial plants, probably due to the ease of laboratory cultivation of these strains. 46% of the reviewed compounds were active against C. albicans, 23% against C. neoformans, 29% against A. fumigatus and only 2% against C. auris. Coculturing was proved to be an effective technique to induce cryptic metabolites absent in other axenic cultures or host extract cultures, with Irperide as the most promising compounds MIC value 1 μg/mL. C. auris was susceptible to only persephacin and rubiginosin C. The latter showed potent inhibition against this recalcitrant strain in a non-fungicide way, which unveils the potential of fungal biofilm inhibition. Further development of culturing techniques and activation of silent metabolic pathways would be favorable to inspire the search for novel bioactive antifungals.

Antimicrobials from endophytes as novel therapeutics to counter drug-resistant pathogens

The rapid increase in antimicrobial resistance (AMR) projects a "global emergency" and necessitates a need to discover alternative resources for combating drug-resistant pathogens or "superbugs." One of the key themes in "One Health Concept" is based on the fact that the interconnected network of humans, the environment, and animal habitats majorly contribute to the rapid selection and spread of AMR. Moreover, the injudicious and overuse of antibiotics in healthcare, the environment, and associated disciplines, further aggravates the concern. The prevalence and persistence of AMR contribute to the global economic burden and are constantly witnessing an upsurge due to fewer therapeutic options, rising mortality statistics, and expensive healthcare. The present decade has witnessed the extensive exploration and utilization of bio-based resources in harnessing antibiotics of potential efficacies. The discovery and characterization of diverse chemical entities from endophytes as potent antimicrobials define an important yet less-explored area in natural product-mediated drug discovery. Endophytes-produced antimicrobials show potent efficacies in targeting microbial pathogens and synthetic biology (SB) mediated engineering of endophytes for yield enhancement, forms a prospective area of research. In keeping with the urgent requirements for new/novel antibiotics and growing concerns about pathogenic microbes and AMR, this paper comprehensively reviews emerging trends, prospects, and challenges of antimicrobials from endophytes and their effective production via SB. This literature review would serve as the platform for further exploration of novel bioactive entities from biological organisms as "novel therapeutics" to address AMR.

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

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

Diversity of endophytic fungi from medicinal plant Oxalis latifolia and their antimicrobial potential against selected human pathogens

Endophytic fungi that inhabit medicinal plants are microbial resources renowned for having compounds analogous to those produced by their host plants. This study aimed to describe the diversity of endophytic fungi found in Oxalis latifolia Kunth. To better understand the diversity of foliar endophytic fungi found in the leaves of the medicinal plant Oxalis latifolia, we isolated and characterized endophytic by using both morphological and molecular methods employing ITS markers. The antimicrobial activity of endophytic fungi against common human pathogens Escherichia coli, Staphylococcus aureus, and Bacillus subtilis was also investigated. A Total of 16 endophytic fungi were successfully isolated from leaves and classified into five orders of Pezizomycotina based on the phylogenic analyses; Xylariales (56%), Diaporthales (19%) Sordariales (6%), Glomerellales (13%) and Botryosphaeriales (6%). The antimicrobial activity of crude extracts from fungal endophyte against Escherichia coli, Staphylococcus aureus, and Bacillus subtilis revealed that three isolates; N. aurantiaca, Phyllosticta capitalensis N. oryzae were the most potent, while Colletotrichum karstii and N. sphaerica displayed no growth inhibition property against the tested organism. The diversity indices were calculated by using the Shannon-Wiener, Margalef, and Simpson indices. The diversity indices analysis revealed an abundance of species diversity, where the dominant species were Nigrospora oryzae, N. sphaerica, and Colletotrichum karstii. This study describes the diversity of endophytic fungi found in O. latifolia and emphasizes their potential as a source of novel bioactive compounds. More research on phytochemical composition and antimicrobial activity is ongoing to correlate the traditional uses and scientific findings.

6-n-Butoxy-10-nitro-12,13-dioxa-11-azatricyclo[7.3.1.02,7]trideca-2,4,6,10-tetraene Improves the X-ray Sensitivity on Inhibiting Proliferation and Promoting Oxidative Stress and Apoptosis of Oral Cancer Cells

This in vitro study examines the anti-oral cancer effects and mechanisms of a combined X-ray/SK2 treatment, i.e., X-ray and 6-n-butoxy-10-nitro-12,13-dioxa-11-azatricyclo[7.3.1.02,7]trideca-2,4,6,10-tetraene (SK2). ATP cell viability and flow cytometry-based cell cycle, apoptosis, oxidative stress, and DNA damage assessments were conducted. The X-ray/SK2 treatment exhibited lower viability in oral cancer (Ca9-22 and CAL 27) cells than in normal (Smulow-Glickman, S-G) cells, i.e., 32.0%, 46.1% vs. 59.0%, which showed more antiproliferative changes than with X-ray or SK2 treatment. Oral cancer cells under X-ray/SK2 treatment showed slight subG1 and G2/M increments and induced high annexin V-monitored apoptosis compared to X-ray or SK2 treatment. The X-ray/SK2 treatment showed higher caspase 3 and 8 levels for oral cancer cells than other treatments. X-ray/SK2 showed a higher caspase 9 level in CAL 27 cells than other treatments, while Ca9-22 cells showed similar levels under X-ray and/or SK2. The X-ray/SK2 treatment showed higher reactive oxygen species (ROS) generation and mitochondrial membrane potential (MMP) depletion than other treatments. Meanwhile, the mitochondrial superoxide (MitoSOX) and glutathione levels in X-ray/SK2 treatment did not exhibit the highest rank compared to others. Moreover, oral cancer cells had higher γH2AX and/or 8-hydroxy-2-deoxyguanosine levels from X-ray/SK2 treatment than others. All these measurements for X-ray/SK2 in oral cancer cells were higher than in normal cells and attenuated by N-acetylcysteine. In conclusion, X-ray/SK2 treatment showed ROS-dependent enhanced antiproliferative, apoptotic, and DNA damage effects in oral cancer cells with a lower cytotoxic influence on normal cells.

Draft genome sequence of endophytic fungus Talaromyces purpureogenus strain YAFEF302, isolated from Juglans sigillata

Here, we report a draft genome sequence of endophytic fungus Talaromyces purpureogenus strain YAFEF302, isolated from Juglans sigillata. The genome resource will support future research into potential secondary metabolite diversity of this fungus.

Diversity and Isolation of Endophytic Fungi in Panax japonicus and Biotransformation Activity on Saponins

OBJECTIVE

This study reports the diversity and community structure differences of the endophytic fungi of Panax japonicus of different ages to obtain novel endophytic fungi with glycoside hydrolytic activity for rare saponins production.

METHODS

This study used the high-throughput sequencing method to analyze the diversity and community structure of endophytic fungi of P. japonicus. The endophytic fungi were processed by traditional isolation, culture, conservation, and ITS rDNA sequence analyses. Then the total saponins of P. japonicus were used as the substrate to evaluate the glycoside hydrolytic activity.

RESULTS

The composition analysis of the community structure showed that the abundance, evenness, and diversity of endophytic fungi of nine-year-old P. japonicus were the best among all samples. A total of 210 endophytic fungi were isolated from P. japonicus samples and further annotated by sequencing the internal transcribed spacer. Then the biotransformation activity of obtained strains was further examined on total saponins of P. japonicus (TSPJ), with a strain identified as Fusarium equiseti (No.30) from 7-year-old P. japonicus showing significant glycoside hydrolytic activity on TSPJ, including ginsenoside Ro→zinglbroside R1, pseudoginsenoside RT1→pseudoginsenoside RP1, chikusetsusaponin IV→tarasaponin VI and chikusetsusaponin IVa →calenduloside E.

CONCLUSION

These results reveal the diversity and community structure differences of the endophytic fungi of P. japonicus with different ages and establish a resource library of endophytic fungi of P. japonicus. More importantly, we identified a valuable endophytic fungus with glycoside hydrolytic activity and provided a promising convenient microbial transformation approach to produce minor deglycosylated ginsenosides.

Study on secondary metabolites of endophytic fungus Diaporthe sp. AC1 induced by tryptophan analogs

Small molecule-induced fermentation of the endophytic fungus Diaporthe sp. AC1 originated from Artemisia argyi was executed to investigate its secondary metabolites. It was fermented in a culture medium containing 5-hydroxytryptophan (5-HTP), 1-methyl-L-tryptophan (1-MT), and tryptamine (TA), respectively. The antibacterial activities of crude extracts against pathogenic bacteria and pathogenic fungi were determined by using the Oxford cup method, while the cytotoxicity of crude extracts against cancer cells was determined by using the MTT method. The results showed that the secondary metabolites of Diaporthe sp. AC1 induced by 1-MT exhibited optimal antibacterial activity and tumor cytotoxicity. The induction conditions of 1-MT were optimized, and the antibacterial activities and tumor cytotoxicity of crude extracts under different induction conditions were investigated. As indicated, the optimal moment for 1-MT addition was before inoculation and its optimal concentration was 0.25 mM. Under these conditions, Diaporthe sp. AC1 was fermented and approximately 12 g of crude extracts was obtained. The crude extracts were then separated and purified to acquire nine monomer compounds, including three new compounds (1-3) and six known compounds (4-9). The antibacterial activities of the compounds against pathogenic bacteria and pathogenic fungi were investigated by using the microdilution method, while their cytotoxicity against cancer cells was analyzed by using the MTT method. The results demonstrated that Compound 1 exhibited moderate antibacterial activities against Verticillium dahlia, Fusarium graminearum, and Botrytis cinerea, as well as a low inhibitory activity against Listeria monocytogenes. Nevertheless, Compound 1 showed significant cytotoxicity against five cancer cells, with IC50 ranging from 12.26 to 52.52 μM. Compounds 2 and 3 exhibited negligible biological activity, while other compounds showed detectable inhibitory activities against pathogenic bacteria and cancer cells.

Persephacin Is a Broad-Spectrum Antifungal Aureobasidin Metabolite That Overcomes Intrinsic Resistance in Aspergillus fumigatus

Fungi pose a persistent threat to humankind with worrying indications that emerging and re-emerging pathogens (e.g., Candida auris, Coccidioides spp., drug-resistant Aspergilli, and more) exhibit resistance to the limited number of approved antifungals. To address this problem, our team is exploring endophytic fungi as a resource for the discovery of new antifungal natural products. The rationale behind this decision is based on evidence that endophytes engage with plants in mutualistic relationships wherein some fungi actively participate by producing chemical defense measures that suppress pathogenic microorganisms. To improve the odds of bioactive metabolite discovery, we developed a new hands-free laser-cutting system capable of generating >50 plant samples per minute that, in turn, enabled our team to prepare and screen large numbers of endophytic fungi. One of the fungal isolates obtained in this way was identified as an Elsinoë sp. that produced a unique aureobasidin analogue, persephacin (1). Some distinctive features of 1 are the absence of both phenylalanine residues combined with the incorporation of a novel amino acid residue, persephanine (9). Compound 1 exhibits potent antifungal effects against a large number of pathogenic yeast (including several clinical C. auris strains), as well as phylogenetically diverse filamentous fungi (e.g., Aspergillus fumigatus). In an ex vivo eye infection model, compound 1 outperformed standard-of-care treatments demonstrating the ability to suppress fluconazole-resistant Candida albicans and A. fumigatus at a concentration (0.1% solution) well below the clinically recommended levels used for fluconazole and natamycin (2% and 5% solutions, respectively). In 3D tissue models for acute dermal and ocular safety, 1 was found to be nontoxic and nonirritating at concentrations required to elicit antifungal activity. Natural product 1 appears to be a promising candidate for further investigation as a broad-spectrum antifungal capable of controlling a range of pathogens that negatively impact human, animal, and plant health.

Fungal Endophytes: Microfactories of Novel Bioactive Compounds with Therapeutic Interventions; A Comprehensive Review on the Biotechnological Developments in the Field of Fungal Endophytic Biology over the Last Decade

The seminal discovery of paclitaxel from endophytic fungus Taxomyces andreanae was a milestone in recognizing the immense potential of endophytic fungi as prolific producers of bioactive secondary metabolites of use in medicine, agriculture, and food industries. Following the discovery of paclitaxel, the research community has intensified efforts to harness endophytic fungi as putative producers of lead molecules with anticancer, anti-inflammatory, antimicrobial, antioxidant, cardio-protective, and immunomodulatory properties. Endophytic fungi have been a valuable source of bioactive compounds over the last three decades. Compounds such as taxol, podophyllotoxin, huperzine, camptothecin, and resveratrol have been effectively isolated and characterized after extraction from endophytic fungi. These findings have expanded the applications of endophytic fungi in medicine and related fields. In the present review, we systematically compile and analyze several important compounds derived from endophytic fungi, encompassing the period from 2011 to 2022. Our systematic approach focuses on elucidating the origins of endophytic fungi, exploring the structural diversity and biological activities exhibited by these compounds, and giving special emphasis to the pharmacological activities and mechanism of action of certain compounds. We highlight the tremendous potential of endophytic fungi as alternate sources of bioactive metabolites, with implications for combating major global diseases. This underscores the significant role that fungi can play in the discovery and development of novel therapeutic agents that address the challenges posed by prevalent diseases worldwide.

Diversity of Fungal Communities on Diseased and Healthy Cinnamomum burmannii Fruits and Antibacterial Activity of Secondary Metabolites

The composition and structure of fungal communities on healthy and diseased fruits of Cinnamomum burmannii (Nees and Nees) Blume were characterized, with evaluation of the antibacterial activity of secondary metabolites from culturable fungi following the first identification of secondary metabolites in the fungus Medicopsis romeroi (Esf-14; GenBank accession number OK242756). These results are significant for understanding the functional variation in bioactivity in fungal communities and developing a broader range of bioactive resources. High-throughput sequencing results indicated that the fungal community in diseased fruit differed from that in healthy fruit at the phylum, class, order, or genus level, with significant differences in the species and relative abundance of the dominant flora. A total of 49 (healthy fruit) and 122 (diseased fruit) artificially cultivable endophytic fungi were isolated, and 41 different strains (11 from healthy fruit and 30 from diseased fruit) were successfully identified by morphological and molecular biological analyses, which were classified into 8 groups and 23 genera by phylogenetic tree analysis, with Pleosporales, Glomerellales, and Hypocreales being the dominant groups at the order level and Colletotrichum being the dominant group at the genus level. The results of the antibacterial assay demonstrated that the secondary metabolites of all strains had different degrees of antibacterial activity, while the secondary metabolites of endophytic fungi from diseased fruit were generally stronger than those of fungi from healthy fruit, with the active secondary metabolites dominated by small and moderately polar compounds. Combined analysis of fungal communities, phylogenetic tree analysis, and bioactivity analysis of culturable strains revealed strong antibacterial activity of both upregulated and downregulated flora in diseased fruit. Five compounds, including two new (5,6-dimethoxy-[1',1:4,1″-terphenyl]-2-ol [compound 1] and 5-(methoxycarbonyl)-2-methylbenzo[d][1,3]dioxole-2-carboxylic acid [compound 2]) and three known compounds (3,7-dihydroxy-1,9-dimethyldibenzofuran [compound 3], methyl 3-hydroxybenzoate [compound 4], and uracil [compound 5]), were isolated and identified for the first time from the endophytic fungus Medicopsis romeroi. In general, the diversity of fungal communities on diseased fruit was lower than that on healthy fruits, while the antibacterial activity of artificially cultured endophytic fungi on diseased fruits was generally stronger than that on healthy fruits, suggesting excellent promise for the development of secondary metabolites from active strains on diseased fruit as antibacterial agents. IMPORTANCE Powdery fruit disease is a notorious disease of Cinnamomum burmannii that causes severe loss in fruit production. Studies on the function of endophytic fungal communities in healthy plant tissues are not new, while little is known about the functional changes of fungal communities in disease-causing plant tissues. Our results demonstrate that fungal communities in diseased fruits differ from those in healthy fruits at the level of phylum, class, order, or genus, with significant differences in the species and relative abundance of dominant groups. Endophytic fungi in diseased fruits appeared to produce secondary metabolites with stronger antibacterial properties, although the community diversity was not as varied as that in healthy fruits. In addition, secondary metabolites of the Medicopsis romeroi strain from diseased fruits were identified for the first time. These results have important implications for understanding the functional variation of bioactivity in fungal communities and for developing a broader resource of bioactivity.

Bioactive compounds and biomedical applications of endophytic fungi: a recent review

Human life has been significantly impacted by the creation and spread of novel species of antibiotic-resistant bacteria and virus strains that are difficult to manage. Scientists and researchers have recently been motivated to seek out alternatives and other sources of safe and ecologically friendly active chemicals that have a powerful and effective effect against a wide variety of pathogenic bacteria as a result of all these hazards and problems. In this review, endophytic fungi and their bioactive compounds and biomedical applications were discussed. Endophytes, a new category of microbial source that can produce a variety of biological components, have major values for study and broad prospects for development. Recently, endophytic fungi have received much attention as a source for new bioactive compounds. In addition, the variety of natural active compounds generated by endophytes is due to the close biological relationship between endophytes and their host plants. The bioactive compounds separated from endophytes are usually classified as steroids, xanthones, terpenoids, isocoumarins, phenols, tetralones, benzopyranones and enniatines. Moreover, this review discusses enhancement methods of secondary metabolites production by fungal endophytes which include optimization methods, co-culture method, chemical epigenetic modification and molecular-based approaches. Furthermore, this review deals with different medical applications of bioactive compounds such as antimicrobial, antiviral, antioxidant and anticancer activities in the last 3 years.

Anti-inflammatory potential of Penicillium brefeldianum endophytic fungus supported with phytochemical profiling

Various factors contribute to the development of the acute inflammation process, like the pro-inflammatory cytokines, certain enzymes as well as oxidative stress mediators. The anti-inflammatory potential of the endophytic fungus Penicillium brefeldianum was explored in carrageenan-induced inflammation in rats. After isolation of the fungus from Acalypha hispida leaves, it was identified by 18S rRNA gene sequencing. Then, its phytochemical profile was elucidated using LC-ESI-MS/MS technique. There was a remarkable decrease in the edema weight in the endophytic fungi-treated group (200 mg/kg). Also, this group had few inflammatory cells and thickened epidermis with underlying moderate collagenosis when stained with haematoxylin and eosin. Besides, immunostaining with monoclonal antibodies of cyclooxygenase-2 and tumor necrosis factor alpha showed a decrease in the positive immune cells in the endophytic fungi treated group (200 mg/kg) in relation to the positive control. Interestingly, the levels of the inflammatory as well as oxidative stress markers, including prostaglandin E2, nitric oxide, and malondialdehyde, which are hallmarks of the inflammatory process, considerably diminished (p < 0.05) in this group. qRT-PCR was utilised to elucidate the impact of the endophytic fungi treatment on the expression of interleukins (IL-1β and IL-6) genes, which decreased in comparison with the positive control group. Consequently, we can deduce that P. brefeldianum endophytic fungus has a promising anti-inflammatory potential and should be extensively studied on a broader range in the near future.

Identification and Mechanism of Action of the Global Secondary Metabolism Regulator SaraC in Stereum hirsutum

DNA methylation is an important factor in the regulation of gene expression. In analyzing genomic data of Stereum hirsutum FP-91666, we found a hypothetical bifunctional transcription regulator/O6Meguanine-DNA methyltransferase (named SaraC), which is widely present in both bacteria and fungi, and confirmed that its function in bacteria is mainly for DNA reparation. In this paper, we confirmed that SaraC has the function of DNA binding and demethylation through surface plasma resonance and reaction experiments in vitro. Then, we achieved the overexpression of SaraC (OES) in S. hirsutum, sequenced the methylation and transcription levels of the whole-genome, and further conducted untargeted metabolomics analyses of the OES transformants and the wild type (WT). The results confirmed that the overall-methylation levels of the transformants were significantly downregulated, and various genes related to secondary metabolism were upregulated. Through comparative untargeted metabolomic analyses, it showed that OES SA6 transformant produced a greater number of hybrid polyketides, and we identified 2 novel hybrid polyketides from the fermentation products of SA6. Our results show that overexpression SaraC can effectively stimulate the expression of secondary-metabolism-related genes, which could be a broad-spectrum tool for discovery of metabolites due to its cross-species conservation. IMPORTANCE Fungi are one of the important sources of active compounds. However, in fungi, most of the secondary metabolic biosynthetic gene clusters are weakly expressed or silenced under conventional culture conditions. How to efficiently excavate potential new compounds contained in fungi is becoming a research hot spot in the world. In this study, we found a DNA demethylation protein (SaraC) and confirmed that it is a global secondary metabolism regulator in Stereum hirsutum FP-91666. In the past, SaraC-like proteins were mainly regarded as DNA repair proteins, but our findings proved that it will be a powerful tool for mining secondary metabolites for overexpression of SaraC, which can effectively stimulate the expression of genes related to secondary metabolism.

Endophytic Diaporthe as Promising Leads for the Development of Biopesticides and Biofertilizers for a Sustainable Agriculture

Plant pathogens are responsible for causing economic and production losses in several crops worldwide, thus reducing the quality and quantity of agricultural supplies. To reduce the usage of chemically synthesized pesticides, strategies and approaches using microorganisms are being used in plant disease management. Most of the studies concerning plant-growth promotion and biological agents to control plant diseases are mainly focused on bacteria. In addition, a great portion of registered and commercialized biopesticides are bacterial-based products. Despite fungal endophytes having been identified as promising candidates for their use in biological control, it is of the utmost importance to develop and improve the existing knowledge on this research field. The genus Diaporthe, encompasses plant pathogens, saprobes and endophytes that have been screened for secondary metabolite, mainly due to their production of polyketides and a variety of unique bioactive metabolites with agronomic importance. Some of these metabolites exhibit antifungal and antibacterial activity for controlling plant pathogens, and phytotoxic activity for the development of potential mycoherbicides. Moreover, species of Diaporthe are reported as promising agents in the development of biofertilizers. For this reason, in this review we summarize the potential of Diaporthe species to produce natural products with application in agriculture and describe the benefits of these fungi to promote their host plant's growth.

Metabolites extracted from microorganisms as potential inhibitors of glycosidases (α-glucosidase and α-amylase): A review

α-Glucosidase and α-amylase are the two main glycosidases that participate in the metabolism of carbohydrates. Inhibitors of these two enzymes are considered an important medical treatment for carbohydrate uptake disorders, such as diabetes and obesity. Microbes are an important source of constituents that have the potential to inhibit glycosidases and can be used as sources of new drugs and dietary supplements. For example, the α-glucosidase inhibitor acarbose, isolated from Actinoplanes sp., has played an important role in adequately controlling type 2 diabetes, but this class of marketed drugs has many drawbacks, such as poor compliance with treatment and expense. This demonstrates the need for new microorganism-derived resources, as well as novel classes of drugs with better compliance, socioeconomic benefits, and safety. This review introduces the literature on microbial sources of α-glucosidase and α-amylase inhibitors, with a focus on endophytes and marine microorganisms, over the most recent 5 years. This paper also reviews the application of glycosidase inhibitors as drugs and dietary supplements. These studies will contribute to the future development of new microorganism-derived glycosidase inhibitors.

Antioral Cancer Effects by the Nitrated [6,6,6]Tricycles Compound (SK1) In Vitro

A novel nitrated [6,6,6]tricycles-derived compound containing nitro, methoxy, and ispropyloxy groups, namely SK1, was developed in our previous report. However, the anticancer effects of SK1 were not assessed. Moreover, SK1 contains two nitro groups (NO2) and one nitrogen-oxygen (N-O) bond exhibiting the potential for oxidative stress generation, but this was not examined. The present study aimed to evaluate the antiproliferation effects and oxidative stress and its associated responses between oral cancer and normal cells. Based on the MTS assay, SK1 demonstrated more antiproliferation ability in oral cancer cells than normal cells, reversed by N-acetylcysteine. This suggests that SK1 causes antiproliferation effects preferentially in an oxidative stress-dependent manner. The oxidative stress-associated responses were further validated, showing higher ROS/MitoSOX burst, MMP, and GSH depletion in oral cancer cells than in normal cells. Meanwhile, SK1 caused oxidative stress-causing apoptosis, such as caspases 3/8/9, and DNA damages, such as γH2AX and 8-OHdG, to a greater extent in oral cancer cells than in normal cells. Siilar to cell viability, these oxidative stress responses were partially diminished by NAC, indicating that SK1 promoted oxidative stress-dependent responses. In conclusion, SK1 exerts oxidative stress, apoptosis, and DNA damage to a greater extent to oral cancer cells than in normal cells.

Is Endophytic Colonization of Host Plants a Method of Alleviating Drought Stress? Conceptualizing the Hidden World of Endophytes

In the wake of changing climatic conditions, plants are frequently exposed to a wide range of biotic and abiotic stresses at various stages of their development, all of which negatively affect their growth, development, and productivity. Drought is one of the most devastating abiotic stresses for most cultivated crops, particularly in arid and semiarid environments. Conventional breeding and biotechnological approaches are used to generate drought-tolerant crop plants. However, these techniques are costly and time-consuming. Plant-colonizing microbes, notably, endophytic fungi, have received increasing attention in recent years since they can boost plant growth and yield and can strengthen plant responses to abiotic stress. In this review, we describe these microorganisms and their relationship with host plants, summarize the current knowledge on how they “reprogram” the plants to promote their growth, productivity, and drought tolerance, and explain why they are promising agents in modern agriculture.

Flavonoids affect the endophytic bacterial community in Ginkgo biloba leaves with increasing altitude

Altitude affects plant growth and metabolism, but the effect of altitude on plant endophytic microorganisms is still unclear. In this study, we selected 16 Ginkgo biloba trees to study the response of leaves' endophytes to flavonoids and altitude (from 530 m to 1,310 m). HPLC results showed that flavonoids in Ginkgo biloba leaves increased by more than 150% with attitude rising from 530 m to 1,310 m, which revealed a positive correlation with altitude. Ginkgo biloba might regulate the increased flavonoids in leaves to resist the increasing light intensity. 16S rDNA sequencing results showed that the endophytic bacterial communities of Ginkgo biloba at different altitudes significantly differed. Ginkgo leaf endophytes' alpha diversity decreased with increasing flavonoids content and altitude. The increased flavonoids might increase the environmental pressure on endophytes and affect the endophytic community in Ginkgo biloba leaves. The bacterial network in Ginkgo biloba leaves became more complex with increasing altitude, which might be one of the strategies of leaf endophytes to cope with increasing flavonoids. Metagenomes results predicted with PICRUSt showed that the abundance of flavonoid biosynthesis and photosynthesis genes were significantly decreased with the increase of flavonoid contents. High flavonoid content in leaves appeared to inhibit microbial flavonoid synthesis. Our findings indicate that altitude can modulate microbial community structure through regulating plant metabolites, which is important to uncovering the interaction of microbes, host and the environment.

Diversity of endophytic fungal community in Huperzia serrata from different ecological areas and their correlation with Hup A content

Background

Huperzine A (Hup A) has attracted considerable attention as an effective therapeutic candidate drug used to treat Alzheimer’s disease. Whereas, the production of Hup A from wild plants faced a major challenge, which is the wild Huperzia Serrata harbor a low Hup A content, has a long-life cycle, and has a small yield. At present, several reports showed that Hup A is produced by various endophytic fungal strains isolated from H. serrata, thereby providing an alternative method to produce the compound and reduce the consumption of this rare and endangered plant. However, till now, very few comprehensive studies are available on the biological diversity and structural composition of endophytic fungi and the effects of endophytic fungi on the Hup A accumulation in H. serrata.

Results

In this research, the composition and diversity of fungal communities in H. serrata were deciphered based on high-throughput sequencing technology of fungal internal transcribed spacer regions2 (ITS2). The correlation between endophytic fungal community and Hup A content was also investigated. Results revealed that the richness and the diversity of endophytic fungi in H. serrata was various according to different tissues and different ecological areas. The endophytic fungal communities of H. serrata exhibit species-specific, ecological-specific, and tissue-specific characteristics. There are 6 genera (Ascomycota_unclassified, Cyphellophora, Fungi_unclassified, Sporobolomyces, and Trichomeriaceae_unclassified) were significantly positively correlated with Hup A content in all two areas, whereas, there are 6 genera (Auricularia, Cladophialophora, Cryptococcus, Mortierella, and Mycena) were significantly negatively correlated with Hup A content of in all two areas.

Conclusions

This study indicated a different composition and diverse endophytic fungal communities in H. serrata from different organs and ecological areas. The current study will provide the realistic basis and theoretical significance for understanding the biological diversity and structural composition of endophytic fungal communities in H. serrata, as well as providing novel insights into the interaction between endophytic fungi and Hup A content.

POTENCY OF ENDOPHYTIC FUNGI ISOLATED FROM Muntingia calabura AS ANTIFUNGAL SUBSTANCES AGAINST Candida parapsilosis

Alternative is needed to overcome the problem of dandruff caused by C. parapsilosis. Endophytic fungi isolated from plants are capable of synthesizing compounds to produce various secondary metabolites. This study aimed to obtain the most active endophytic fungal isolates, determine the class of compounds, and determine the antifungal activity of the endophytic fungi (M. calabura) against C. parapsilosis.  Fifteen isolates of endophytic fungi isolated from M. calabura were coded FDK1-FDK15. There was a color change in the media after 30 days of cultivation isolates of fungi. FDK4 and FDK13 have potential as antifungals. FDK13 fungal extract had the highest inhibition zone diameter of 20.00 mm. 20 eluates were obtained from the isolation of com-pounds (Thin Layer Chromatography), FDK 131, 1314, 1317, and 1320 eluates are compounds of the terpenoid group and FDK1316 eluates are phenol group compounds that are active in inhibiting yeast growth. FDK1317 was the most active compound isolate in inhibiting the growth of C. parapsilosis with an inhibition zone diameter of 12.5 mm.

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.

Combined Treatment of Nitrated [6,6,6]Tricycles Derivative (SK2)/Ultraviolet C Highly Inhibits Proliferation in Oral Cancer Cells In Vitro

Combined treatment is an effective strategy to improve anticancer therapy, but severe side effects frequently limit this application. Drugs inhibiting the proliferation of cancer cells, but not normal cells, display preferential antiproliferation to cancer cells. It shows the benefits of avoiding side effects and enhancing antiproliferation for combined treatment. Nitrated [6,6,6]tricycles derivative (SK2), a novel chemical exhibiting benzo-fused dioxabicyclo[3.3.1]nonane core with an n-butyloxy substituent, exhibiting preferential antiproliferation, was chosen to evaluate its potential antioral cancer effect in vitro by combining it with ultraviolet C (UVC) irradiation. Combination treatment (UVC/SK2) caused lower viability in oral cancer cells (Ca9-22 and OC-2) than single treatment (20 J/m² UVC or 10 μg/mL SK2), i.e., 42.3%/41.1% vs. 81.6%/69.2%, and 89.5%/79.6%, respectively. In contrast, it showed a minor effect on cell viability of normal oral cells (HGF-1), ranging from 82.2 to 90.6%. Moreover, UVC/SK2 caused higher oxidative stress in oral cancer cells than normal cells through the examination of reactive oxygen species, mitochondrial superoxide, and mitochondrial membrane potential. UVC/SK2 also caused subG1 increment associated with apoptosis detections by assessing annexin V; panaspase; and caspases 3, 8, and 9. The antiproliferation and oxidative stress were reverted by N-acetylcysteine, validating the involvement of oxidative stress in antioral cancer cells. UVC/SK2 also caused DNA damage by detecting γH2AX and 8-hydroxy-2′-deoxyguanosine in oral cancer cells. In conclusion, SK2 is an effective enhancer for improving the UVC-caused antiproliferation against oral cancer cells in vitro. UVC/SK2 demonstrated a preferential and synergistic antiproliferation ability towards oral cancer cells with little adverse effects on normal cells.

Diversity and Ginsenoside Biotransformation Potential of Cultivable Endophytic Fungi Associated With Panax bipinnatifidus var. bipinnatifidus in Qinling Mountains, China

To obtain novel fungi with potent β-glucosidase for minor ginsenoside production, Panax bipinnatifidus var. bipinnatifidus, which is a traditional medicinal plant containing various ginsenosides, was first employed to isolate endophytic fungi in this study. A total of 93 representative morphotype strains were isolated and identified according to ITS rDNA sequence analyses, and they were grouped into three phyla (Ascomycota, Basidiomycota, and Mucoromycota), five classes (Dothideomycetes, Sordariomycetes, Eurotiomycetes, Agaricomycetes, and Mucoromycetes), and 24 genera. Plectosphaerella (RA, 19.35%) was the most abundant genus, followed by Paraphoma (RA, 11.83%) and Fusarium (RA, 9.70%). The species richness index (S, 34) and the Shannon–Wiener index (H’, 3.004) indicated that P. bipinnatifidus harbored abundant fungal resources. A total of 26 endophytic fungal ethyl acetate extracts exhibited inhibitory activities against at least one pathogenic bacterium or fungus. In total, 11 strains showed strong β-glucosidase activities and also presented with the ability of ginsenoside biotransformation with varied glycoside-hydrolyzing pathways. Excitingly, three genera, namely, Ilyonectria, Sarocladium, and Lecanicillium, and all 11 taxa were first found to have the ability to transform ginsenosides in our study. The results indicated that P. bipinnatifidus could be a new fungi resource with potential novel natural compounds with antimicrobial activity and potent β-glucosidase for varied minor ginsenoside production.

Metabolites of soil microorganisms modulate amyloid β production in Alzheimer's neurons

Microbial flora is investigated to be related with neuropathological conditions in Alzheimer’s disease (AD), and is attracting attention as a drug discovery resource. However, the relevance between the soil microbiota and the pathological condition has not been fully clarified due to the difficulty in isolation culture and the component complexity. In this study, we established a library of secondly metabolites produced in microorganism to investigate the potential effect of microorganisms on the production of amyloid β (Aβ), one of the most representative pathogens of AD. We conducted a library screening to quantify Aβ and neuronal toxicity by using cortical neurons from human induced pluripotent stem cells (iPSCs) of AD patients after adding secondary metabolites. Screening results and following assessment of dose-dependency identified Verrucarin A, produced in Myrothecium spp., showed 80% decrease in Aβ production. Furthermore, addition of Mer-A2026A, produced in Streptomyces pactum, showed increase in Aβ42/40 ratio at the low concentration, and decrease in Aβ production at the higher concentration. As a result, established library and iPSC-based phenotyping assay clarified a direct link between Aβ production and soil microorganisms. These results suggest that Aβ-microorganism interaction may provide insight into the AD pathophysiology with potential therapeutics.

Antiproliferation- and Apoptosis-Inducible Effects of a Novel Nitrated [6,6,6]Tricycle Derivative (SK2) on Oral Cancer Cells

The benzo-fused dioxabicyclo[3.3.1]nonane core is the central framework in several natural products. Using this core, we had developed a novel nitrated [6,6,6]tricycle-derived compound containing an n-butyloxy group, namely, SK2. The anticancer potential of SK2 was not assessed. This study aimed to determine the antiproliferative function and investigated possible mechanisms of SK2 acting on oral cancer cells. SK2 preferentially killed oral cancer cells but caused no harmful effect on non-malignant oral cells. After the SK2 exposure of oral cancer cells, cells in the sub-G1 phase accumulated. This apoptosis-like outcome of SK2 treatment was validated to be apoptosis via observing an increasing annexin V population. Mechanistically, apoptosis signalers such as pancaspase, caspases 8, caspase 9, and caspase 3 were activated by SK2 in oral cancer cells. SK2 induced oxidative-stress-associated changes. Furthermore, SK2 caused DNA damage (γH2AX and 8-hydroxy-2′-deoxyguanosine). In conclusion, a novel nitrated [6,6,6]tricycle-derived compound, SK2, exhibits a preferential antiproliferative effect on oral cancer cells, accompanied by apoptosis, oxidative stress, and DNA damage.

Polyketide Derivatives from the Endophytic Fungus Phaeosphaeria sp. LF5 Isolated from Huperzia serrata and Their Acetylcholinesterase Inhibitory Activities

The secondary metabolites of Phaeosphaeria sp. LF5, an endophytic fungus with acetylcholinesterase (AChE) inhibitory activity isolated from Huperzia serrata, were investigated. Their structures and absolute configurations were elucidated by means of extensive spectroscopic data, including one- and two-dimensional nuclear magnetic resonance (NMR), high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) analyses, and calculations of electronic circular dichroism (ECD). A chemical study on the solid-cultured fungus LF5 resulted in 11 polyketide derivatives, which included three previously undescribed derivatives: aspilactonol I (4), 2-(1-hydroxyethyl)-6-methylisonicotinic acid (7), and 6,8-dihydroxy-3-(1′R, 2′R-dihydroxypropyl)-isocoumarin (9), and two new natural-source-derived aspilactonols (G, H) (2, 3). Moreover, the absolute configuration of de-O-methyldiaporthin (11) was identified for the first time. Compounds 4 and 11 exhibited inhibitory activity against AChE with half maximal inhibitory concentration (IC₅₀) values of 6.26 and 21.18 µM, respectively. Aspilactonol I (4) is the first reported furanone AChE inhibitor (AChEI). The results indicated that Phaeosphaeria is a good source of polyketide derivatives. This study identified intriguing lead compounds for further research and development of new AChEIs.

Endophytic Fungi: An Effective Alternative Source of Plant-Derived Bioactive Compounds for Pharmacological Studies

Plant-associated fungi (endophytic fungi) are a biodiversity-rich group of microorganisms that are normally found asymptomatically within plant tissues or in the intercellular spaces. Endophytic fungi promote the growth of host plants by directly producing secondary metabolites, which enhances the plant's resistance to biotic and abiotic stresses. Additionally, they are capable of biosynthesizing medically important "phytochemicals" that were initially thought to be produced only by the host plant. In this review, we summarized some compounds from endophyte fungi with novel structures and diverse biological activities published between 2011 and 2021, with a focus on the origin of endophytic fungi, the structural and biological activity of the compounds they produce, and special attention paid to the exploration of pharmacological activities and mechanisms of action of certain compounds. This review revealed that endophytic fungi had high potential to be harnessed as an alternative source of secondary metabolites for pharmacological studies.

Endophytic Fungi Isolated from Baccharis linearis and Echinopsis chiloensis with Antifungal Activity against Botrytis cinerea

Botrytis cinerea is one of the most important phytopathogens in agriculture worldwide, infecting economically important crops. The main control of this fungus is by synthetic fungicides, causing the selection of resistant isolates. Compounds produced by endophytic fungi have been shown to have antifungal activity against this pathogen and can be used as an alternative to synthetic fungicides. The aim of this work was to isolate endophytic fungi from Chilean foothills in the Metropolitan Region. Ten fungi were isolated from Echinopsis chiloensis and Baccharis linearis, however, only two isolates inhibited the mycelial growth of B. cinerea by antibiosis and were identified as Epicoccum sp. and Pleosporales sp. Extracts at 200 mg L⁻¹ from Epicoccum sp. and Pleosporales sp. showed antifungal activity against B. cinerea of 54.6 and 44.6% respectively. Active compounds in the Epicoccum sp. extracts were mainly alkaloids and phenolic compounds; meanwhile, in the Pleosporales sp. extracts, terpenes and/or saponins were responsible for the antifungal activity.

Fungal Endophytes: A Potential Source of Antibacterial Compounds

Antibiotic resistance is becoming a burning issue due to the frequent use of antibiotics for curing common bacterial infections, indicating that we are running out of effective antibiotics. This has been more obvious during recent corona pandemics. Similarly, enhancement of antimicrobial resistance (AMR) is strengthening the pathogenicity and virulence of infectious microbes. Endophytes have shown expression of various new many bioactive compounds with significant biological activities. Specifically, in endophytic fungi, bioactive metabolites with unique skeletons have been identified which could be helpful in the prevention of increasing antimicrobial resistance. The major classes of metabolites reported include anthraquinone, sesquiterpenoid, chromone, xanthone, phenols, quinones, quinolone, piperazine, coumarins and cyclic peptides. In the present review, we reported 451 bioactive metabolites isolated from various groups of endophytic fungi from January 2015 to April 2021 along with their antibacterial profiling, chemical structures and mode of action. In addition, we also discussed various methods including epigenetic modifications, co-culture, and OSMAC to induce silent gene clusters for the production of noble bioactive compounds in endophytic fungi.

Multigene Phylogeny, Diversity and Antimicrobial Potential of Endophytic Sordariomycetes From Rosa roxburghii

Rosa roxburghii Tratt. is widely applied in food, cosmetics, and traditional medicine, and has been demonstrated to possess diverse bioactivities. Plant endophytic fungi are important microbial resources with great potential for application in many fields. They not only establish mutualistic symbiosis with host plants but also produce a variety of bioactive compounds. Therefore, in the present study, endophytic fungi were isolated from R. roxburghii, the diversity and antimicrobial activities were evaluated. As a result, 242 strains of endophytic Sordariomycetes were successfully isolated. Multigene phylogenetic analyses showed that these isolates included eight orders, 19 families, 33 genera. The dominant genera were Diaporthe (31.4%), Fusarium (14.4%), Chaetomium (7.9%), Dactylonectria (7.0%), Graphium (4.5%), Colletotrichum (4.1%), and Clonostachys (4.1%). For different tissues of R. roxburghii, alpha diversity analysis revealed that the diversity of fungal communities decreased in the order of root, fruit, stem, flower, leaf, and seed, and Clonostachys and Dactylonectria exhibited obvious tissue specificity. Meanwhile, functional annotation of 33 genera indicated that some fungi have multitrophic lifestyles combining endophytic, pathogenic, and saprophytic behavior. Additionally, antimicrobial activities of endophytic Sordariomycetes against Lasiodiplodia theobromae, Botryosphaeria dothidea, Colletotrichum capsici, Pyricularia oryzae, Rhizoctonia solani, Fusarium oxysporum, Pseudomonas syringae, Pantoea agglomerans, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa were screened. Dual culture test assays showed that there were 40 different endophytic species with strong inhibition of at least one or moderate inhibition of two or more against the 12 tested strains. The results from the filter paper diffusion method suggested that extracellular metabolites may be more advantageous than intracellular metabolites in the development of antimicrobial agents. Eleven isolates with good activities were screened. In particular, Hypomontagnella monticulosa HGUP194009 and Nigrospora sphaerica HGUP191020 have shown promise in both broad-spectrum and intensity. Finally, some fungi that commonly cause disease have been observed to have beneficial biological activities as endophytic fungi. In conclusion, this study showed the species composition, alpha diversity, and lifestyle diversity of endophytic Sordariomycetes from R. roxburghii and demonstrated these isolates are potential sources for exploring antimicrobial agents.

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

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

Plant associated fungal endophytes as a source of natural bioactive compounds

Endophytes are a potent source of bioactive compounds that mimic plant-based metabolites. The relationship of host plant and endophyte is significantly associated with alteration in fungal colonisation and the extraction of endophyte-derived bioactive compounds. Screening of fungal endophytes and their relationship with host plants is essential for the isolation of bioactive compounds. Numerous bioactive compounds with antioxidant, antimicrobial, anticancer, and immunomodulatory properties are known to be derived from fungal endophytes. Bioinformatics tools along with the latest techniques such as metabolomics, next-generation sequencing, and metagenomics multilocus sequence typing can potentially fill the gaps in fungal endophyte research. The current review article focuses on bioactive compounds derived from plant-associated fungal endophytes and their pharmacological importance. We conclude with the challenges and opportunities in the research area of fungal endophytes.

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

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

Fungal Biofilms as a Valuable Target for the Discovery of Natural Products That Cope with the Resistance of Medically Important Fungi-Latest Findings

The development of new antifungal agents that target biofilms is an urgent need. Natural products, mainly from the plant kingdom, represent an invaluable source of these entities. The present review provides an update (2017-May 2021) on the available information on essential oils, propolis, extracts from plants, algae, lichens and microorganisms, compounds from different natural sources and nanosystems containing natural products with the capacity to in vitro or in vivo modulate fungal biofilms. The search yielded 42 articles; seven involved essential oils, two Brazilian propolis, six plant extracts and one of each, extracts from lichens and algae/cyanobacteria. Twenty articles deal with the antibiofilm effect of pure natural compounds, with 10 of them including studies of the mechanism of action and five dealing with natural compounds included in nanosystems. Thirty-seven manuscripts evaluated Candida spp. biofilms and two tested Fusarium and Cryptococcus spp. Only one manuscript involved Aspergillus fumigatus. From the data presented here, it is clear that the search of natural products with activity against fungal biofilms has been a highly active area of research in recent years. However, it also reveals the necessity of deepening the studies by (i) evaluating the effect of natural products on biofilms formed by the newly emerged and worrisome health-care associated fungi, C. auris, as well as on other non-albicans Candida spp., Cryptococcus sp. and filamentous fungi; (ii) elucidating the mechanisms of action of the most active natural products; (iii) increasing the in vivo testing.

Marine endophytic fungal metabolites: A whole new world of pharmaceutical therapy exploration

The growing threat arises due to diseases such as cancer and the infections around the world leading to a critical requirement for novel and constructive compounds with unique ways of action capable of combating these deadly diseases. At present, it is evident that endophytic fungi constitute an enormous as well as comparatively untapped source of great biodiversity that can be considered as a wellspring of effective novel natural products for medical, agricultural and industrial use. Marine endophytic fungi have been found in every marine plants (algae, seagrass, driftwood, mangrove plants), marine vertebrates (mainly, fish) or marine invertebrates (mainly, sponge and coral) inter- and intra-cellular without causing any palpable symptoms of illness. Since evolution of microbes and eukaryotes to a higher level, coevolution has resulted in specific interaction mechanisms. Endophytic fungi are known to influence the life cycle and are necessary for the homeostasis of their eukaryotic hosts and the chemical signals of their host have been shown to activate gene expression in endophytes to induce expression of endophytic secondary metabolites. Marine endophytic fungi are receiving increasing attention by chemists because of their varied and structurally unmatched compounds that have strong biological roles in life as lead pharmaceutical compounds, including anticancer, antiviral, insulin mimetic, antineurodegenerative, antimicrobial, antioxidant and immuno-suppressant compounds. Moreover, fungal endophytes proved to have different biological activities for exploitation in the environmental and agricultural sustainability.

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.

Endophytic Fungal Community of Huperzia serrata: Diversity and Relevance to the Production of Huperzine A by the Plant Host

As the population ages globally, there seem to be more people with Alzheimer's disease. Unfortunately, there is currently no specific treatment for the disease. At present, Huperzine A (HupA) is one of the best drugs used for the treatment of Alzheimer's disease and has been used in clinical trials for several years in China. HupA was first separated from Huperzia serrata, a traditional medicinal herb that is used to cure fever, contusions, strains, hematuria, schizophrenia, and snakebite for several hundreds of years in China, and has been confirmed to have acetylcholinesterase inhibitory activity. With the very slow growth of H. serrata, resources are becoming too scarce to meet the need for clinical treatment. Some endophytic fungal strains that produce HupA were isolated from H. serrate in previous studies. In this article, the diversity of the endophytic fungal community within H. serrata was observed and the relevance to the production of HupA by the host plant was further analyzed. A total of 1167 strains were obtained from the leaves of H. serrata followed by the stems (1045) and roots (824). The richness as well as diversity of endophytic fungi within the leaf and stem were higher than in the root. The endophytic fungal community was similar within stems as well as in leaves at all taxonomic levels. The 11 genera (Derxomyces, Lophiostoma, Cyphellophora, Devriesia, Serendipita, Kurtzmanomyces, Mycosphaerella, Conoideocrella, Brevicellicium, Piskurozyma, and Trichomerium) were positively correlated with HupA content. The correlation index of Derxomyces with HupA contents displayed the highest value (CI = 0.92), whereas Trichomerium showed the lowest value (CI = 0.02). Through electrospray ionization mass spectrometry (ESI-MS), it was confirmed that the HS7-1 strain could produce HupA and the total alkaloid concentration was 3.7 ug/g. This study will enable us to screen and isolate the strain that can produce HupA and to figure out the correlation between endophytic fungal diversity with HupA content in different plant organs. This can provide new insights into the screening of strains that can produce HupA more effectively.

Itaconic acid derivatives: structure, function, biosynthesis, and perspectives

Itaconic acid possessing a vinylidene group, which is mainly produced by fungi, is used as a biobased platform chemical and shows distinctive bioactivities. On the other hand, some fungi and lichens produce itaconic acid derivatives possessing itaconic acid skeleton, and the number of the derivatives is currently more than seventy. Based on the molecular structures, they can be categorized into two groups, alkylitaconic acids and α-methylene-γ-butyrolactones. Interestingly, some itaconic acid derivatives show versatile functions such as antimicrobial, anti-inflammatory, antitumor, and plant growth-regulating activities. The vinylidene group of itaconic acid derivatives likely participates in these functions. It is suggested that α-methylene-γ-butyrolactones are biosynthesized from alkylitaconic acids which are first biosynthesized from acyl-CoA and oxaloacetic acid. Some modifying enzymes such as hydroxylase and dehydratase are likely involved in the further modification after biosynthesis of their precursors. This contributes to the diversity of itaconic acid derivatives. In this review, we summarize their structures, functions, and biosynthetic pathways together with a discussion of a strategy for the industrial use. KEY POINTS: • Itaconic acid derivatives can be categorized into alkylitaconic acids and α-methylene-γ-butyrolactones. • The vinylidene group of itaconic acid derivatives likely participates in their versatile function. • It is suggested that α-methylene-γ-butyrolactones are biosynthesized from alkylitaconic acids which are first synthesized from acyl-CoA and oxaloacetic acid.

Endophytic Fungi Isolated from Plants Growing in Central Andean Precordillera of Chile with Antifungal Activity against Botrytis cinerea

Botrytis cinerea is an important phytopathogenic fungus affecting the fruit production around the world. This fungus is controlled mainly by using synthetic fungicides, but many resistant isolates have been selected by the indiscriminate use of fungicides. Endophytic fungi or secondary metabolites obtained from them become an alternative method of control for this fungus. The aim of this work was to identify endophytic fungi with antifungal activity against the plant pathogenic fungus B. cinerea isolated from plants from Central Andean Precordillera of Chile. Three endophytic fungi (Ac1, Lc1 and Ec1) with antifungal activity against B. cinerea were isolated from native and endemic plants growing in Central Andean Precordillera of Chile. The isolates Lc1 (isolated from Lithraea caustica) and Ac1 (isolated from Acacia caven) were identified as Alternaria spp. and the isolate Ec1 (isolated from Echinopsis chiloensis) was identified as Aureobasidium spp. The isolated endophytic fungi would inhibit B. cinerea through the secretion of diffusible and volatile compounds affecting the mycelial growth, conidia germination and interestingly, it was also shown that the volatile compounds produced by the three isolated endophytic fungi suppressed the sporulation of B. cinerea.

Diversity and Antimicrobial Activity of Endophytic Fungi Isolated from Chloranthus japonicus Sieb in Qinling Mountains, China

The plant Chloranthus japonicus Sieb is known for its anticancer properties and mainly distributed in China, Japan, and Korea. In this study, we firstly investigated the diversity and antimicrobial activity of the culturable endophytic fungi from C. japonicus. A total of 332 fungal colonies were successfully isolated from 555 tissue segments of the medicinal plant C. japonicus collected from Qinling Mountains, China. One hundred and thirty representative morphotype strains were identified according to ITS rDNA sequence analyses and were grouped into three phyla (Ascomycota, Basidiomycota, Mucoromycota), five classes (Dothideomycetes, Sordariomycetes, Eurotiomycetes, Agaricomycetes, Mucoromycetes), and at least 30 genera. Colletotrichum (RA, 60.54%) was the most abundant genus, followed by Aspergillus (RA, 11.75%) and Diaporthe (RA, 9.34%). The Species Richness Index (S, 56) and the Shannon-Wiener Index (H', 2.7076) indicated that C. japonicus harbored abundant fungal resources. Thirteen out of 130 endophytic fungal ethyl acetate extracts exhibited inhibitory activities against at least one pathogenic bacterium or fungus. Among of these, F8158, which was identified as Trichoderma cf. harzianum, exhibited good antagonistic capacities (the percent inhibition of mycelial growth ranged from 47.72~88.18) for different pathogens and has a potential application in biological control. In addition, it is noteworthy that the strain F8157 (Thanatephorus cucumeris, an opportunistic pathogen) showed antibacterial and antifungal activity, which is reported firstly in this study, and should be investigated further. Taken together, these results indicated that the endophytic fungi from C. japonicus may be of potential interest in screening bio-control agents and discovering of new bioactive compounds.

Diversity and Bioactivity of Endophytes From Angelica sinensis in China

Plant seeds are not merely reproductive organs, they are also carriers of microorganism, particularly, inherent and non-invasive characteristic endophytes in host plant. Therefore, in this study, the endophytic diversity of Angelica seeds was studied and compared with endophytes isolated from healthy leaves, stems, roots, and seeds of A. sinensis using 20 different media. The metabolites of endophytic strains were evaluated with six different methods for their antioxidant activity and the paper disc diffusion method for antimicrobial activities. As a result, 226 endophytes were isolated. Compared with the biodiversity and abundance of uncultured fungi from Angelica seed, the result showed that the most frequent endophytic fungi were Alternaria sp. as seen in artificial media; moreover, compared with artificial media, the pathogenic fungi, including Fusarium sp. and Pseudallescheria sp., were not found from the Angelica seed, the results suggested it may not be inherent endophytes in plants. In addition, bacteria from seven phyla were identified by high-throughput sequencing, while five phyla of endophytic bacteria were not isolated on artificial media including Proteobacteria, Actinobacteria, Bacteroidetes, Microgenomates, and Saccharibacteria. Furthermore, the sample JH-4 mycelium displayed the best antioxidant activity, and the active constituent may be a flavonoid as determined by total phenol and flavonoid content. Moreover, YH-12-1 mycelium had strong inhibitory activity against the five tested strains and the minimum inhibitory concentration (MIC) against Pseudomonas aeruginosa and Streptococcus pneumoniae was found to be 25 μg/mL. Our results confirm that plant endophytes are rich in biodiversity and contain important resource of many uncultured microorganisms.

Diversity of Physiological and Biochemical Characters of Microdochium Fungi

The biological characterization of Microdochium majus, M. nivale, and M. seminicola strains with wide geographical origins showed the diversity of their pathogenic properties and metabolite compounds, allowing them to exist in their habitats. Significant differences in the ability of Microdochium fungi to cause lesions on wheat and oat leaves were found. The intensity of symptoms depended on the species and substrate origin of the strains. On average M. seminicola strains were able to cause less leaf necrosis than M. majus and M. nivale. The volatile organic compound (VOC) profile of Microdochium fungi included 29 putative fungal metabolites. The spectrum of the identified VOCs in M. seminicola strains was much richer than that in M. majus and M. nivale strains. In addition, the strains of M. seminicola emitted at least six sesquiterpenes. Mycotoxin analysis by HPLC/MS/MS revealed that the analyzed Microdochium strains did not produce any toxic metabolites typically produced by filamentous fungi.