Antimicrobial and cytotoxic secondary metabolites from tropical leaf endophytes: Isolation of antibacterial agent pyrrocidine C from Lewia infectoria SNB-GTC2402

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.

Activation of secondary metabolite gene clusters in Chaetomium olivaceum via the deletion of a histone deacetylase

Histone acetylation modifications in filamentous fungi play a crucial role in epigenetic gene regulation and are closely linked to the transcription of secondary metabolite (SM) biosynthetic gene clusters (BGCs). Histone deacetylases (HDACs) play a pivotal role in determining the extent of histone acetylation modifications and act as triggers for the expression activity of target BGCs. The genus Chaetomium is widely recognized as a rich source of novel and bioactive SMs. Deletion of a class I HDAC gene of Chaetomium olivaceum SD-80A, g7489, induces a substantial pleiotropic effect on the expression of SM BGCs. The C. olivaceum SD-80A ∆g7489 strain exhibited significant changes in morphology, sporulation ability, and secondary metabolic profile, resulting in the emergence of new compound peaks. Notably, three polyketides (A1-A3) and one asterriquinone (A4) were isolated from this mutant strain. Furthermore, our study explored the BGCs of A1-A4, confirming the function of two polyketide synthases (PKSs). Collectively, our findings highlight the promising potential of molecular epigenetic approaches for the elucidation of novel active compounds and their biosynthetic elements in Chaetomium species. This finding holds great significance for the exploration and utilization of Chaetomium resources. KEY POINTS: • Deletion of a class I histone deacetylase activated secondary metabolite gene clusters. • Three polyketides and one asterriquinone were isolated from HDAC deleted strain. • Two different PKSs were reported in C. olivaceum SD-80A.

Microascones, Decahydrofluorene-Class Alkaloids from the Marine-Derived Fungus Microascus sp. SCSIO 41821

Eight new decahydrofluorene-class alkaloids, microascones A and B (1 and 2), 2,3-epoxyphomapyrrolidone C (3), 14,16-epiascomylactam B (4), 24-hydroxyphomapyrrolidone A (5), and microascones C-E (6-8), along with five known analogs (9-13) were isolated from the marine-derived fungus Microascus sp. SCSIO 41821. Compounds 1 and 2 have an unprecedented complex macrocyclic alkaloid skeleton with a 6/5/6/5/6/5/13 polycyclic system. Their structures and absolute configurations were determined by spectroscopic analysis, quantum chemical calculations of ECD spectra, and 13C NMR chemical shifts. Compounds 10-13 showed selective enzyme inhibitory activity against PTPSig, PTP1B, and CDC25B, and 4, 9, and 10 exhibited strong antibacterial activity against seven tested pathogens. Their structure-bioactivity relationship was discussed, and a plausible biosynthetic pathway for 1-8 was also proposed.

Embellicines C-E: Macrocyclic Alkaloids with a Cyclopenta[b]fluorene Ring System from the Fungus Sarocladium sp

Macrocyclic alkaloids with a cyclopenta[b]fluorene ring system are a relatively young structural class of fungal metabolites, with the first members reported in 2013. Bioassay-guided fractionation of a Sarocladium sp. (fungal strain MSX6737) led to a series of both known and new members of this structural class (1-5), including the known embellicine A (1), three new embellicine analogues (2, 4, and 5), and a semisynthetic acetylated analogue (3). The structures were identified by examining both high-resolution electrospray ionization mass spectrometry data and one-dimensional and two-dimensional NMR spectra. The relative configurations of these molecules were established via 1H-1H coupling constants and nuclear Overhauser effect spectroscopy, while comparisons of the experimental electronic circular dichroism (ECD) spectra with the time-dependent density functional theory ECD calculations were utilized to assign their absolute configurations, which were in good agreement with the literature. These alkaloids (1-5) showed cytotoxic activity against a human breast cancer cell line (MDA-MB-231) that ranged from 0.4 to 4.8 μM. Compounds 1 and 5 were also cytotoxic against human ovarian (OVCAR3) and melanoma (MDA-MB-435) cancer cell lines.

A Meroterpenoid from Tibetan Medicine Induces Lung Cancer Cells Apoptosis through ROS-Mediated Inactivation of the AKT Pathway

As a traditional Tibetan medicine in China, Meconopsis grandis Prain has been used to treat a variety of illnesses by local people for thousands of years. However, the active ingredients contained in Meconopsis grandis Prain and its pharmacodynamic mechanisms have scarcely been reported. We isolated a meroterpenoid named D1399 from Meconopsis grandis Prain endophytic fungi with strong antitumor activity. The structure analysis showed that D1399 is an alkaloid containing a 13-membered macrocyclic structure. The IC₅₀ of D1399 for human lung cancer cells' viability ranged from 0.88 to 2.45 μM. Furthermore, we utilized TUNEL assay and western blotting to investigate the antitumor effectiveness of D1399. The results have shown that D1399 induced the apoptosis of lung cancer cells on the extrinsic and intrinsic pathways by boosting ROS generation and repressing AKT activity. In the mouse xenograft model, the average tumor weight with 30 mg·kg^-1 D1399 treatment exhibited 73.19% inhibition compared with the untreated control, without affecting body weight loss. Above all, for the first time, our study provides a possible mechanism for the antitumor activity of D1399 in vitro and in vivo as a natural product from Tibetan medicine with Meconopsis grandis Prain, which may be a potentially promising antitumor drug candidate.

Perspectives and potential applications of endophytic microorganisms in cultivation of medicinal and aromatic plants

Ensuring food and nutritional security, it is crucial to use chemicals in agriculture to boost yields and protect the crops against biotic and abiotic perturbations. Conversely, excessive use of chemicals has led to many deleterious effects on the environment like pollution of soil, water, and air; loss of soil fertility; and development of pest resistance, and is now posing serious threats to biodiversity. Therefore, farming systems need to be upgraded towards the use of biological agents to retain agricultural and environmental sustainability. Plants exhibit a huge and varied niche for endophytic microorganisms inside the planta, resulting in a closer association between them. Endophytic microorganisms play pivotal roles in plant physiological and morphological characteristics, including growth promotion, survival, and fitness. Their mechanism of action includes both direct and indirect, such as mineral phosphate solubilization, fixating nitrogen, synthesis of auxins, production of siderophore, and various phytohormones. Medicinal and aromatic plants (MAPs) hold a crucial position worldwide for their valued essential oils and several phytopharmaceutically important bioactive compounds since ancient times; conversely, owing to the high demand for natural products, commercial cultivation of MAPs is on the upswing. Furthermore, the vulnerability to various pests and diseases enforces noteworthy production restraints that affect both crop yield and quality. Efforts have been made towards enhancing yields of plant crude drugs by improving crop varieties, cell cultures, transgenic plants, etc., but these are highly cost-demanding and time-consuming measures. Thus, it is essential to evolve efficient, eco-friendly, cost-effective simpler approaches for improvement in the yield and health of the plants. Harnessing endophytic microorganisms as biostimulants can be an effective and alternative step. This review summarizes the concept of endophytes, their multidimensional interaction inside the host plant, and the salient benefits associated with endophytic microorganisms in MAPs.

Pyrrospirones K-Q, Decahydrofluorene-Class Alkaloids from the Marine-Derived Fungus Penicillium sp. SCSIO 41512

Seven new decahydrofluorene-class alkaloids, pyrrospirones K-Q (1-7), together with six known analogues (8-13) were isolated from the marine-derived fungal strain Penicillium sp. SCSIO 41512. Their structures were determined by extensive spectroscopic analysis, and their absolute configurations were established by single-crystal X-ray diffraction analysis and quantum chemical calculations of electronic circular dichroism spectra. Compounds 1 and 3 possess a novel decahydrofluorene-class alkaloid skeleton with a 6/5/6/8/5/6/13 and a 6/5/6/5/6/13 polycyclic system, respectively. Biologically, 13 displayed significant inhibitory activity against protein tyrosine phosphatases CD45, TCPTP, SHP1, and PTP1B with IC₅₀ values of 8.1-17.8 μM, and 1, 2, 5, 8-10, 12, and 13 showed antibacterial activity against six pathogens. Their structure-activity relationship is also discussed.

Community composition, bacterial symbionts, antibacterial and antioxidant activities of honeybee-associated fungi

Background

Fungi associated with insects represent one potentially rich source for the discovery of novel metabolites. However, a comprehensive understanding of the fungal communities of Apis mellifera ligustica remains elusive.

Results

Here, we investigated the phylogenetic diversity and community composition of honeybee-associated fungi using combination of culture-dependent and culture-independent approaches. A total of forty-five fungi were isolated and purified from the Apis mellifera ligustica, royal jelly, and honeycomb, which belonged to four classes and eleven different genera. Furthermore, 28 bacterial 16S rRNA gene sequences were obtained by PCR from the fungal metagenome. High-throughput sequencing analyses revealed that the fungal communities were more diverse, a total of 62 fungal genera were detected in the honeybee gut by culture-independent method, whereas only 4 genera were isolated by culture-dependent method. Similarly, 247 fungal genera were detected in the honeycomb, whereas only 4 genera were isolated. In addition, we assessed the antibacterial and antioxidant activities of fungal isolates. Most fungal crude extracts obtained from the cultivation supernatant exhibited antioxidant activities. Only two fungal crude extracts displayed moderate activity against Escherichia coli and Staphylococcus aureus. Chemical analysis of Chaetomium subaffine MFFC22 led to the discovery of three known compounds, including cochliodinol (1), emodin (2), chrysophanol (3). Among them, cochliodinol (1) showed intense DPPH radical scavenging activity with the 50% inhibitory concentration (IC₅₀) of 3.06 μg/mL, which was comparable to that of the positive ascorbic acid (IC₅₀ = 2.25 μg/mL). Compound 2 displayed weak inhibitory activities against Micrococcus tetragenus and S. aureus.

Conclusions

This research provided a fundamental clue for the complex interactions among honeybees, fungi, bacterial symbionts, and the effects on the honeybee. Furthermore, the diversity of honeybee-associated fungi had great potential in finding the resource of new species and antioxidants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02580-4.

Identification of Antagonistic Compounds between the Palm Tree Xylariale Endophytic Fungi and the Phytopathogen Fusarium oxysporum

To discover microorganisms that naturally possess chemical weapons against the phytopathogen Fusarium oxysporum, the biological and chemical diversity of plant leaf endophytes was investigated. Endophytes were isolated from the palm tree Astrocaryum sciophyllum collected in pristine forests of French Guiana. Several Xylariaceae inhibited the growth of F. oxysporum and were further explored. Antifungal specialized metabolites were isolated from the Xylariaceae BSNB-0294 strain in confrontation with the phytopathogen and led to the identification of undescribed compounds, i.e., two depsipeptides named xylariaceins, two metabolites containing a 3-imidazolinone moiety, and four new compounds including a nitro-phenylpropanamide and three phenylalanine analogues named xylariains A-D. In parallel, the chemical investigation of the phytopathogen during the coculture led to the identification of an unknown compound, which we named focicin. The production of focicin was exacerbated during the competition. Matrix-assisted laser desorption/ionization coupled to time-of-flight mass spectometry (MALDI-TOF MS) imaging of the competition between BSNB-0294 (endophytic strain) and F. oxysporum f.sp. ciceris (phytopathogen) highlighted time-dependent chemical interactions between the two microorganisms.

Deep learning approaches for natural product discovery from plant endophytic microbiomes

Plant microbiomes are not only diverse, but also appear to host a vast pool of secondary metabolites holding great promise for bioactive natural products and drug discovery. Yet, most microbes within plants appear to be uncultivable, and for those that can be cultivated, their metabolic potential lies largely hidden through regulatory silencing of biosynthetic genes. The recent explosion of powerful interdisciplinary approaches, including multi-omics methods to address multi-trophic interactions and artificial intelligence-based computational approaches to infer distribution of function, together present a paradigm shift in high-throughput approaches to natural product discovery from plant-associated microbes. Arguably, the key to characterizing and harnessing this biochemical capacity depends on a novel, systematic approach to characterize the triggers that turn on secondary metabolite biosynthesis through molecular or genetic signals from the host plant, members of the rich 'in planta' community, or from the environment. This review explores breakthrough approaches for natural product discovery from plant microbiomes, emphasizing the promise of deep learning as a tool for endophyte bioprospecting, endophyte biochemical novelty prediction, and endophyte regulatory control. It concludes with a proposed pipeline to harness global databases (genomic, metabolomic, regulomic, and chemical) to uncover and unsilence desirable natural products.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1186/s40793-021-00375-0.

Bioprospecting of endophytic microorganisms for bioactive compounds of therapeutic importance

Presently, several drug discovery investigations on therapeutic management of human health are aimed at bioprospecting for microorganisms, especially endophytic microbes of biotechnological importance. This review investigates the benefits of endophytes, especially in producing bioactive compounds useful in modern medicine by systematically reviewing published data from 12 databases. Only experimental studies investigating either or both bacterial and fungal endophytes and within the scope of this review were selected. The published data from the last 2 decades (2000-2019) revealed diverse endophytes associated with different plants produce a broad spectrum of bioactive compounds with therapeutic benefits. Notably, antibacterial, followed by anticancer and antifungal activities, were mostly reported. Only three studies investigated the anti-plasmodial activity. The variation observed in the synthesis of bioactive compounds amongst endophytes varied with host type, endophyte species, and cultivation medium. Fungal endophytes were more investigated than bacterial endophytes, with both endophytes having species diversity amongst literature. The endophytes were predominantly from medicinal plants and belonged to either Ascomycota (fungi) or Proteobacteria and Firmicutes (bacteria). This review presents excellent prospects of harnessing endophytes and their unique bioactive compounds in developing novel and effective compounds of medicinal importance.

A Review on Antistaphylococcal Secondary Metabolites from Basidiomycetes

Fungi are a rich source of secondary metabolites with several pharmacological activities such as antifungal, antioxidant, antibacterial and anticancer to name a few. Due to the large number of diverse structured chemical compounds they produce, fungi from the phyla Ascomycota, Basidiomycota and Muccoromycota have been intensively studied for isolation of bioactive compounds. Basidiomycetes-derived secondary metabolites are known as a promising source of antibacterial compounds with activity against Gram-positive bacteria. The continued emergence of antimicrobial resistance (AMR) poses a major challenge to patient health as it leads to higher morbidity and mortality, higher hospital-stay duration and substantial economic burden in global healthcare sector. One of the key culprits for AMR crisis is Staphylococcus aureus causing community-acquired infections as the pathogen develops resistance towards multiple antibiotics. The recent emergence of community strains of S. aureus harbouring methicillin-resistant (MRSA), vancomycin-intermediate (VISA) and vancomycin-resistant (VRSA) genes associated with increased virulence is challenging. Despite the few significant developments in antibiotic research, successful MRSA therapeutic options are still needed to reduce the use of scanty and expensive second-line treatments. This paper provides an overview of findings from various studies on antibacterial secondary metabolites from basidiomycetes, with a special focus on antistaphylococcal activity.

Identification and dereplication of endophytic Colletotrichum strains by MALDI TOF mass spectrometry and molecular networking

The chemical diversity of biologically active fungal strains from 42 Colletotrichum, isolated from leaves of the tropical palm species Astrocaryum sciophilum collected in pristine forests of French Guiana, was investigated. The collection was first classified based on protein fingerprints acquired by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) correlated with cytotoxicity. Liquid chromatography coupled to high-resolution tandem mass spectrometry (LC-HRMS/MS) data from ethyl acetate extracts were acquired and processed to generate a massive molecular network (MN) using the MetGem software. From five Colletotrichum strains producing cytotoxic specialized metabolites, we predicted the occurrence of peptide and cytochalasin analogues in four of them by MN, including a similar ion clusters in the MN algorithm provided by MetGem software. Chemoinformatics predictions were fully confirmed after isolation of three pentacyclopeptides (cyclo(Phe-Leu-Leu-Leu-Val), cyclo(Phe-Leu-Leu-Leu-Leu) and cyclo(Phe-Leu-Leu-Leu-Ile)) and two cytochalasins (cytochalasin C and cytochalasin D) exhibiting cytotoxicity at the micromolar concentration. Finally, the chemical study of the last active cytotoxic strain BSNB-0583 led to the isolation of four colletamides bearing an identical decadienamide chain.

Carneic Acids from an Endophytic Phomopsis sp. as Dengue Virus Polymerase Inhibitors

Thirteen carneic acids were isolated from the fungal endophyte Phomopsis sp. SNB-LAP1-7-32. Their structures were identified by mass spectrometry and extensive one- and two-dimensional NMR spectroscopy and through comparison with data reported in the literature. Compounds 1-13 were investigated for their antipolymerase activities against DENV polymerase and Zika NS5. Five of them exhibited significant inhibition of dengue polymerase with IC₅₀ values in the 10 to 20 μM range without cytotoxicity. None inhibited Zika virus NS5 protein.

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.

In Vitro Antimalarial and Toxicological Activities of Quercus infectoria (Olivier) Gall Extracts

BACKGROUND

The spread of Plasmodium falciparum resistance in common antimalarial drugs, including artemisinin-based combination therapies, has necessitated the discovery of new drugs with novel mechanisms of action. In the present study, the in vitro antimalarial and toxicological activities of acetone, methanol, ethanol and aqueous extracts of Quercus infectoria (Q. infectoria) galls were investigated.

METHODS

The extracts were assessed for the antimalarial potential using a malarial SYBR Green I fluorescence-based (MSF) assay, while the toxicity was screened by using brine shrimp lethality test (BSLT), haemolytic assay, and cytotoxicity assay against normal embryo fibroblast cell line (NIH/3T3) and normal kidney epithelial cell line (Vero).

RESULTS

The acetone extract showed the highest antimalarial activity (50% inhibitory concentration, IC50 = 5.85 ± 1.64 μg/mL), followed by the methanol extract (IC50 = 10.31 ± 1.90 μg/mL). Meanwhile, the ethanol and aqueous extracts displayed low antimalarial activity with IC50 values of 20.00 ± 1.57 and 30.95 μg/mL ± 1.27 μg/mL, respectively. The significant antimalarial activity was demonstrated in all extracts and artemisinin (P < 0.05). All extracts were non-toxic to brine shrimps (50% lethality concentration, LC50 > 1000 ppm). Furthermore, no occurrence of haemolysis (< 5%) was observed in normal erythrocytes when treated with all extracts compared to Triton X-100 that caused 100% haemolysis (P < 0.05). The acetone and methanol extracts were non-toxic to the normal cell lines and statistically significant to artemisinin (P < 0.05).

CONCLUSION

Taken together with satisfactory selectivity index (SI) values, the acetone and methanol extracts of Q. infectoria galls could serve as an alternative, promising and safe antimalarial agents.

Natural Bioactive Compounds from Fungi as Potential Candidates for Protease Inhibitors and Immunomodulators to Apply for Coronaviruses

The inhibition of viral protease is an important target in antiviral drug discovery and development. To date, protease inhibitor drugs, especially HIV-1 protease inhibitors, have been available for human clinical use in the treatment of coronaviruses. However, these drugs can have adverse side effects and they can become ineffective due to eventual drug resistance. Thus, the search for natural bioactive compounds that were obtained from bio-resources that exert inhibitory capabilities against HIV-1 protease activity is of great interest. Fungi are a source of natural bioactive compounds that offer therapeutic potential in the prevention of viral diseases and for the improvement of human immunomodulation. Here, we made a brief review of the current findings on fungi as producers of protease inhibitors and studies on the relevant candidate fungal bioactive compounds that can offer immunomodulatory activities as potential therapeutic agents of coronaviruses in the future.

Metabolomic-guided discovery of cyclic nonribosomal peptides from Xylaria ellisii sp. nov., a leaf and stem endophyte of Vaccinium angustifolium

Fungal endophytes are sources of novel bioactive compounds but relatively few agriculturally important fruiting plants harboring endophytes have been carefully studied. Previously, we identified a griseofulvin-producing Xylaria species isolated from Vaccinium angustifolium, V. corymbosum, and Pinus strobus. Morphological and genomic analysis determined that it was a new species, described here as Xylaria ellisii. Untargeted high-resolution LC-MS metabolomic analysis of the extracted filtrates and mycelium from 15 blueberry isolates of this endophyte revealed differences in their metabolite profiles. Toxicity screening of the extracts showed that bioactivity was not linked to production of griseofulvin, indicating this species was making additional bioactive compounds. Multivariate statistical analysis of LC-MS data was used to identify key outlier features in the spectra. This allowed potentially new compounds to be targeted for isolation and characterization. This approach resulted in the discovery of eight new proline-containing cyclic nonribosomal peptides, which we have given the trivial names ellisiiamides A-H. Three of these peptides were purified and their structures elucidated by one and two-dimensional nuclear magnetic resonance spectroscopy (1D and 2D NMR) and high-resolution tandem mass spectrometry (HRMS/MS) analysis. The remaining five new compounds were identified and annotated by high-resolution mass spectrometry. Ellisiiamide A demonstrated Gram-negative activity against Escherichia coli BW25113, which is the first reported for this scaffold. Additionally, several known natural products including griseofulvin, dechlorogriseofulvin, epoxy/cytochalasin D, zygosporin E, hirsutatin A, cyclic pentapeptides #1–2 and xylariotide A were also characterized from this species.

Didymellanosine, a new decahydrofluorene analogue, and ascolactone C from Didymella sp. IEA-3B.1, an endophyte of Terminalia catappa

Didymellanosine (1), the first analogue of the decahydrofluorene-class of natural products bearing a 13-membered macrocyclic alkaloid conjugated with adenosine, and a new benzolactone derivative, ascolactone C (4) along with eight known compounds (2, 3, 5-10), were isolated from a solid rice fermentation of the endophytic fungus Didymella sp. IEA-3B.1 derived from the host plant Terminalia catappa. In addition, ascochitamine (11) was obtained when (NH4)2SO4 was added to rice medium and is reported here for the first time as a natural product. Didymellanosine (1) displayed strong activity against the murine lymphoma cell line L5178Y, Burkitt's lymphoma B cells (Ramos) and adult lymphoblastic leukemia T cells (Jurkat J16), with IC50 values of 2.0, 3.3 and 4.4 µM, respectively. When subjected to a NFκB inhibition assay, didymellanosine (1) moderately blocked NFκB activation in the triple-negative breast cancer cell line MDA-MB 231. In an antimicrobial assay, ascomylactam C (3) was the most active compound when tested against a panel of Gram-positive bacteria including drug-resistant strains with MICs of 3.1-6.3 µM, while 1 revealed weaker activity. Interestingly, both compounds were also found active against Gram-negative Acinetobacter baumannii with MICs of 3.1 µM, in the presence of a sublethal concentration (0.1 µM) of colistin.

Identification of Antimicrobial Compounds from Sandwithia guyanensis-Associated Endophyte Using Molecular Network Approach

The emergence of multidrug resistant bacterial pathogens and the increase of antimicrobial resistance constitutes a major health challenge, leading to intense research efforts being focused on the discovery of novel antimicrobial compounds. In this study, endophytes were isolated from different parts of Sandwithia guyanensis plant (leaves, wood and latex) belonging to the Euphorbiaceae family and known to produce antimicrobial compounds, and chemically characterised using Molecular Network in order to discover novel antimicrobial molecules. One fungal endophyte extract obtained from S. guyanensis latex showed significant antimicrobial activity with Minimal Inhibitory Concentration on methicillin-resistant Staphylococcus aureus at 16 µg/mL. The chemical investigation of this fungus (Lecanicillium genus) extract led to the isolation of 5 stephensiolides compounds, four of which demonstrated antibacterial activity. Stephensiolide I and G showed the highest antibacterial activity on MRSA with a MIC at 4 and 16 µg/mL respectively.

Ascomylactams A-C, Cytotoxic 12- or 13-Membered-Ring Macrocyclic Alkaloids Isolated from the Mangrove Endophytic Fungus Didymella sp. CYSK-4, and Structure Revisions of Phomapyrrolidones A and C

Three new 12- or 13-membered-ring macrocyclic alkaloids, named ascomylactams A-C (1-3), along with the analogues phomapyrrolidone C (4) and phomapyrrolidone A (5) were isolated from the mangrove endophytic fungus Didymella sp. CYSK-4. Their structures were elucidated by analysis of extensive spectroscopic data and mass spectrometric data. The structures and absolute configurations of 1 and 2 were determined by single-crystal X-ray diffraction experiments, which represents the first crystal structures described for a (6/5/6/5) tetracyclic skeleton fused with a 12- or 13-membered-ring macrocyclic moiety. The configurations of phomapyrrolidone C (4) and phomapyrrolidone A (5) were revised by detailed analysis of the NMR data. In a cytotoxic assay, compounds 1 and 3 showed moderate cytotoxicity against MDA-MB-435, MDA-MB-231, SNB19, HCT116, NCI-H460, and PC-3 human cancer cell lines, with IC₅₀ values in the range of 4.2-7.8 μM.

Promising Alternative Therapeutics for Oral Candidiasis

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Candida is the main human fungal pathogen causing infections (candidiasis), mostly in the elderly and immunocompromised hosts. Even though Candida spp. is a member of the oral microbiota in symbiosis, in some circumstances, it can cause microbial imbalance leading to dysbiosis, resulting in oral diseases. Alternative therapies are urgently needed to treat oral candidiasis (usually associated to biofilms), as several antifungal drugs’ activity has been compromised. This has occurred especially due to an increasing occurrence of drugresistant in Candida spp. strains. The overuse of antifungal medications, systemic toxicity, cross-reactivity with other drugs and a presently low number of drug molecules with antifungal activity, have contributed to important clinical limitations.

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We undertook a structured search of bibliographic databases (PubMed Central, Elsevier’s ScienceDirect, SCOPUS and Springer’s SpringerLink) for peer-reviewed research literature using a focused review in the areas of alternatives to manage oral candidiasis. The keywords used were “candidiasis”, “oral candidiasis”, “biofilm + candida”, “alternative treatment”, “combination therapy + candida” and the reports from the last 10 to 15 years were considered for this review.

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This review identified several promising new approaches in the treatment of oral candidiasis: combination anti-Candida therapies, denture cleansers, mouth rinses as alternatives for disrupting candidal biofilms, natural compounds (e.g. honey, probiotics, plant extracts and essential oils) and photodynamic therapy.

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The findings of this review confirm the importance and the urgency of the development of efficacious therapies for oral candidal infections.

Structural Identification of Antibacterial Lipids from Amazonian Palm Tree Endophytes through the Molecular Network Approach

A library of 197 endophytic fungi and bacteria isolated from the Amazonian palm tree Astrocaryum sciophilum was extracted and screened for antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). Four out of five antibacterial ethyl acetate extracts were also cytotoxic for the MRC-5 cells line. Liquid chromatography coupled to tandem mass spectrometry (UPHLC-HRMS/MS) analyses combined with molecular networking data processing were carried out to allow the identification of depsipeptides and cyclopeptides responsible for the cytotoxicity in the dataset. Specific ion clusters from the active Luteibacter sp. extract were also highlighted using an MRSA activity filter. A chemical study of Luteibacter sp. was conducted leading to the structural characterization of eight fatty acid exhibiting antimicrobial activity against MRSA in the tens of µg/mL range.

Anti-glioma trichobamide A with an unprecedented tetrahydro-5H-furo[2,3-b]pyrrol-5-one functionality from ascidian-derived fungus Trichobotrys effuse 4729

Trichobamide A (1), a novel pyrrocidine alkaloid with an unprecedented tetrahydro-5H-furo[2,3-b]pyrrol-5-one moiety, was isolated from the ascidian-derived fungus Trichobotrys effuse 4729.

Anti-quorum sensing and antibiofilm potential of Alternaria alternata, a foliar endophyte of Carica papaya, evidenced by QS assays and in-silico analysis

In the present study, secondary metabolites from an endophytic fungus, Alternaria alternata, colonizing Carica papaya, demonstrated antiquorum sensing properties against Pseudomonas aeruginosa. This study reports the antagonistic effects of fungal crude extract of A. alternata against the various quorum sensing (QS) associated virulent factors such as percentage decrease in production of pyocyanin, alginate, chitinase and rhamnolipid; significant decrease in proteases activity such as LasA protease activity, staphylolytic activity, Las B elastase; and a marked decrease in biofilm formation and associated factors such as exopolysaccharide (EPS) production and cell surface hydrophobicity (CSH). Further, motility pattern i.e., swimming and swarming was also found to be inhibited. This down regulation of QS and associated factors are further supported by in-silico analysis of interaction between QS receptor LasR and bioactive molecules viz., sulfurous acid, 2-propyl tridecyl ester and 1,2-benzenedicarboxylic acid, bis(2-methylpropyl) ester present in fungal crude extract, found based on GCMS analysis, sketches the modulating ability of QS expression. This is the first report on an endophytic fungus of C. papaya having a role in QS inhibition against P. aeruginosa and lays a platform to explore further the endophytes for potent therapeutic agents in QS.

Diversity of cultivable fungal endophytes in Paullinia cupana (Mart.) Ducke and bioactivity of their secondary metabolites

Paullinia cupana is associated with a diverse community of pathogenic and endophytic microorganisms. We isolated and identified endophytic fungal communities from the roots and seeds of P. cupana genotypes susceptible and tolerant to anthracnose that grow in two sites of the Brazilian Amazonia forest. We assessed the antibacterial, antitumor and genotoxic activity in vitro of compounds isolated from the strains Trichoderma asperellum (1BDA) and Diaporthe phaseolorum (8S). In concert, we identified eight fungal species not previously reported as endophytes; some fungal species capable of inhibiting pathogen growth; and the production of antibiotics and compounds with bacteriostatic activity against Pseudomonas aeruginosa in both susceptible and multiresistant host strains. The plant genotype, geographic location and specially the organ influenced the composition of P. cupana endophytic fungal community. Together, our findings identify important functional roles of endophytic species found within the microbiome of P. cupana. This hypothesis requires experimental validation to propose management of this microbiome with the objective of promoting plant growth and protection.

A new amino amidine derivative from the wood-decaying fungus Xylaria cf. cubensis SWUF08-86

The secondary metabolites of Xylaria cf. cubensis SWUF08-86 fungus were investigated, and the chromatographic separation of the crude extracts yielded seventeen compounds. The structure elucidation by spectroscopic analysis including 1D and 2D NMR and the comparison of these data with literature, along with HREIMS spectrometry, revealed one new amino amidine derivative (1), together with five known simple cyclic dipeptide analogs, diketopiperazines (2-6) and eleven other known compounds, including one hemi-cycline (10), three aromatic derivatives (11-13), one sesquiterpene (14) and three sterols (15-17). The isolated compounds were screened for anticancer and anti-pathogenic bacterial and fungal activities. Based on this work, Xylaria cf. cubensis SWUF08-86 has proven to be a diverse secondary metabolites producer.

Candida glabrata Biofilms: How Far Have We Come?

Infections caused by Candida species have been increasing in the last decades and can result in local or systemic infections, with high morbidity and mortality. After Candida albicans, Candida glabrata is one of the most prevalent pathogenic fungi in humans. In addition to the high antifungal drugs resistance and inability to form hyphae or secret hydrolases, C. glabrata retain many virulence factors that contribute to its extreme aggressiveness and result in a low therapeutic response and serious recurrent candidiasis, particularly biofilm formation ability. For their extraordinary organization, especially regarding the complex structure of the matrix, biofilms are very resistant to antifungal treatments. Thus, new approaches to the treatment of C. glabrata's biofilms are emerging. In this article, the knowledge available on C. glabrata's resistance will be highlighted, with a special focus on biofilms, as well as new therapeutic alternatives to control them.

Betulinic Acid, The First Lupane-Type Triterpenoid Isolated from Both a Phomopsis sp. and Its Host Plant Diospyros carbonaria Benoist

Following a biological screening using a dengue replicon virus-cell-based assay, Diospyros carbonaria AcOEt extract was investigated, affording six known lupane-type triterpenoids endowed with anti-DENV-2 NS5 polymerase activity. The study of the associated microbial community of this species permitted us to identify 38 endophytes belonging to five different orders. Nine out of these 38 strains showed significant activity on the dengue replicon assay. The chemical investigation of the most active one, Phomopsis sp. SNB-LAP1-7-32, led to the isolation of betulinic acid, an anti-viral secondary metabolite isolated previously from the host plant. This result is the first example of a lupane-type triterpenoid isolated from both an endophyte and its host plant. Its presence in the Phomopsis strain may result from gene transfer and/or specific niche selection.

Two New Secondary Metabolites from the Endophytic Fungus Endomelanconiopsis endophytica

Two new secondary metabolites, endomeketals A–B (1–2), a new natural product (3), and a known compound (4) were isolated from the ethyl acetate extract of the endophytic fungus Endomelanconiopsis endophytica A326 derived from Ficus hirta. Their structures were determined on the basis of extensive spectroscopic analysis. All compounds were evaluated for their cytotoxic activities against SF-268, MCF-7, NCI-H460, and HepG-2 tumor cell lines. However, no compound showed cytotoxic activity against these human tumor cell lines.

Isolation and characterization of culturable seed-associated bacterial endophytes from gnotobiotically grown Marama bean seedlings

Marama bean (Tylosema esculentum) is an indigenous non-nodulating legume to the arid agro-ecological parts of Southern Africa. It is a staple food for the Khoisan and Bantu people from these areas. It is intriguing how it is able to synthesize the high-protein content in the seeds since its natural habitat is nitrogen deficient. The aim of the study was to determine the presence of seed transmittable bacterial endophytes that may have growth promoting effects, which may be particularly important for the harsh conditions. Marama bean seeds were surface sterilized and gnotobiotically grown to 2 weeks old seedlings. From surface-sterilized shoots and roots, 123 distinct bacterial isolates were cultured using three media, and identified by BOX-PCR fingerprinting and sequence analyses of the 16S rRNA and nifH genes. Phylogenetic analyses of 73 putative endophytes assigned them to bacterial species from 14 genera including Proteobacteria (Rhizobium, Massilia, Kosakonia, Pseudorhodoferax, Caulobacter, Pantoea, Sphingomonas, Burkholderia, Methylobacterium), Firmicutes (Bacillus), Actinobacteria (Curtobacterium, Microbacterium) and Bacteroidetes (Mucilaginibacter, Chitinophaga). Screening for plant growth-promoting activities revealed that the isolates showed production of IAA, ACC deaminase, siderophores, endoglucanase, protease, AHLs and capacities to solubilize phosphate and fix nitrogen. This is the first report that marama bean seeds may harbor endophytes that can be cultivated from seedlings; in this community of bacteria, physiological characteristics that are potentially plant growth promoting are widespread.

Contributions of North American endophytes to the phylogeny, ecology, and taxonomy of Xylariaceae (Sordariomycetes, Ascomycota)

The Xylariaceae (Sordariomycetes) comprise one of the largest and most diverse families of Ascomycota, with at least 85 accepted genera and ca. 1343 accepted species. In addition to their frequent occurrence as saprotrophs, members of the family often are found as endophytes in living tissues of phylogenetically diverse plants and lichens. Many of these endophytes remain sterile in culture, precluding identification based on morphological characters. Previous studies indicate that endophytes are highly diverse and represent many xylariaceous genera; however, phylogenetic analyses at the family level generally have not included endophytes, such that their contributions to understanding phylogenetic relationships of Xylariaceae are not well known. Here we use a multi-locus, cumulative supermatrix approach to integrate 92 putative species of fungi isolated from plants and lichens into a phylogenetic framework for Xylariaceae. Our collection spans 1933 isolates from living and senescent tissues in five biomes across the continental United States, and here is analyzed in the context of previously published sequence data from described species and additional taxon sampling of type specimens from culture collections. We found that the majority of strains obtained in our surveys can be classified in the hypoxyloid and xylaroid subfamilies, although many also were found outside of these lineages (as currently circumscribed). Many endophytes were placed in lineages previously not known for endophytism. Most endophytes appear to represent novel species, but inferences are limited by potential gaps in public databases. By linking our data, publicly available sequence data, and records of ascomata, we identify many geographically widespread, host-generalist clades capable of symbiotic associations with diverse photosynthetic partners. Concomitant with such cosmopolitan host use and distributions, many xylariaceous endophytes appear to inhabit both living and non-living plant tissues, with potentially important roles as saprotrophs. Overall, our study reveals major gaps in the availability of multi-locus datasets and metadata for this iconic family, and provides new hypotheses regarding the ecology and evolution of endophytism and other trophic modes across the family Xylariaceae.

Secondary Metabolites Isolated from the Amazonian Endophytic Fungus Diaporthe sp. SNB-GSS10

We describe a Sabicea cinerea endophytic fungus closely related to Diaporthe pseudomangiferae that produces two known metabolites, mycoepoxydiene (1) and altiloxin A (2), as well as enamidin (3) and eremofortin F (4), two compounds not previously described in the literature. The structure of these four metabolites was elucidated using spectroscopic analysis, and their cytotoxic activities were measured against the human cell lines KB, MRC-5, and MDA-MB-435.

Plants and endophytes: equal partners in secondary metabolite production?

Well known plant production systems should be re-evaluated due to findings that the interesting metabolite might actually be produced by microbes intimately associated with the plant, so-called endophytes. Endophytes can be bacteria or fungi and they are characterized usually by the feature that they do not cause any harm to the host. Indeed, in some cases, such as mycorrhizal fungi or other growth promoting endophytes, they can be beneficial for the plant. Here some examples are reviewed where the host plant and/or endophyte metabolism can be induced by the other partner. Also, partial or complete biosynthesis pathways for plant secondary metabolites can be attributed to such endophytes. In other cases the host plant is able to metabolize substances from fungal origin. The question of the natural role of such metabolic changes for the endophyte will be briefly touched. Finally, the consequences for the use of plant cultures for secondary metabolite production is discussed.

Antibacterial ilicicolinic acids C and D and ilicicolinal from Neonectria discophora SNB-CN63 isolated from a termite nest

Ilicicolinic acids A, C, and D (1-3) and ilicicolinal (4) were isolated from a fungus isolated from a Nasutitermes corniger nest in French Guiana. The structures of ilicicolinic acids C and D and ilicicolinal were elucidated using 1D and 2D NMR spectroscopic data as well as MS data. Ilicicolinic acids show antibacterial activity in vitro.