New phytotoxic metabolites from Pestalotiopsis sp. HC02, a Fungus Residing in Chondracris rosee gut

Antibacterial and cytotoxic metabolites produced by Streptomyces tanashiensis BYF-112 isolated from Odontotermes formosanus

Chemical investigations of the termite-associated Streptomyces tanashiensis BYF-112 resulted in the discovery of four novel alkaloid derivatives: vegfrecines A and B (1 and 2), exfoliazone A (3), and venezueline H (7), in addition to nine known metabolites (4-6, 8-13). The structures of these compounds were elucidated through comprehensive spectroscopic analysis and comparison with existing literature data. Antibacterial assays revealed that viridomycin A (11) exhibited potent antibacterial activity against Staphylococcus aureus, with a zone of inhibition (ZOI) of 12.67 mm, in comparison to a ZOI of 17.67 mm for the positive control gentamicin sulfate. Viridomycin A (11) showed moderate activity against Micrococcus tetragenus and Pseudomonas syringae pv. actinidae, with ZOI values of 15.50 and 14.33 mm, respectively, which were inferior to those of gentamicin sulfate (34.67 and 24.00 mm). Viridomycin F (12) also exhibited moderate antibacterial effects against S. aureus, M. tetragenus, and P. syringae pv. actinidae, with ZOI values of 8.33, 16.50, and 10.83 mm, respectively. Cytotoxicity assays demonstrated that viridobruunine A (5), exfoliazone (6), viridomycin A (11), and X-14881E (13) exhibited significant cytotoxicity against human malignant melanoma (A375), ovarian cancer (SKOV-3), and gastric cancer (MGC-803) cell lines, with IC50 values ranging from 4.61 to 19.28 μmol·L-1. Furthermore, bioinformatic analysis of the complete genome of S. tanashiensis suggested a putative biosynthetic gene cluster (BGC) responsible for the production of compounds 1-12. These findings indicate that the secondary metabolites of insect-associated S. tanashiensis BYF-112 hold promise as potential sources of novel antibacterial and anticancer agents.

Identification of fungus-growing termite-associated halogenated-PKS maduralactomycin a as a potential inhibitor of MurF protein of multidrug-resistant Acinetobacter baumannii

Multidrug-resistant Acinetobacter baumannii infections have become a major public health concern globally. Inhibition of its essential MurF protein has been proposed as a potential target for broad-spectrum drugs. This study aimed to evaluate the potential of a novel ecological niche of 374 fungus-growing termite associated Natural Products (NPs). The molecular docking and computational pharmacokinetics screened four compounds, i.e., Termstrin B, Fridamycin A, Maduralactomycin A, and Natalenamide C, as potential compounds that have higher binding affinities and favourable protein-ligand interactions. The compound Maduralactomycin A induced more stability based on its lowest average RMSD value (2.31 Å) and low standard deviation (0.35) supported by the consistent flexibility and β-factor during the protein's time-dependent motion. While hydrogen bond analysis indicated that Termstrin B has formed the strongest intra-protein interaction, solvent accessibility was in good agreement with Maduralactomycin A compactness. Maduralactomycin A has the strongest binding energy among all the compounds (-348.48 kcal/mol) followed by Termstrin B (-321.19 kcal/mol). Since these findings suggest Maduralactomycin A and Termstrin B as promising candidates for inhibition of MurF protein, the favourable binding energies of Maduralactomycin A make it a more important compound to warrant further investigation. However, experimental validation using animal models and clinical trials is recommended before reaching any final conclusions.

Pestalotiopsis Diversity: Species, Dispositions, Secondary Metabolites, and Bioactivities

Pestalotiopsis species have gained attention thanks to their structurally complex and biologically active secondary metabolites. In past decades, several new secondary metabolites were isolated and identified. Their bioactivities were tested, including anticancer, antifungal, antibacterial, and nematicidal activity. Since the previous review published in 2014, new secondary metabolites were isolated and identified from Pestalotiopsis species and unidentified strains. This review gathered published articles from 2014 to 2021 and focused on 239 new secondary metabolites and their bioactivities. To date, 384 Pestalotiopsis species have been discovered in diverse ecological habitats, with the majority of them unstudied. Some may contain secondary metabolites with unique bioactivities that might benefit pharmacology.

Inhibitory Effects of Carbazomycin B Produced by Streptomyces roseoverticillatus 63 Against Xanthomonas oryzae pv. oryzae

The present manuscript highlights the potential role of Streptomyces roseoverticillatus 63 (Sr-63) against Xanthomonas oryzae pv. oryzae (Xoo), which is the cause of a disastrous bacterial leaf blight disease with rice worldwide. The disease suppression was achieved under greenhouse conditions. A foliar spray of the fermentation broth of Sr-63 significantly reduced the leaf blight symptoms with rice in Xoo inoculated rice plants. Furthermore, we observed that the carbazomycin B, isolated from the fermentation broth of Sr-63, was demonstrated to have antibacterial activity against Xoo with a minimum inhibitory concentration (MIC) of 8 μg mL-1. The results indicated that carbzomycin B hampered the membrane formation of Xoo, reduced the production of xanthomonadin and extracellular polymeric substance (EPS). The fourier transform infrared spectroscopic (FT-IR) indicated that carbazomycin B changed the components of the cell membrane, then caused a change of the cell surface hydrophobicity of Xoo. Scanning electron microscopy revealed that the Xoo cells treated with carbazomycin B exhibited apparent structural deformation. The results also indicated that carbazomycin B had a negative impact on the metabolism of Xoo, carbazomycin B reduced the activity of malate dehydrogenase (MDH) activity and suppressed the protein expression of Xoo. Overall, our data suggests that Streptomyces roseoverticillatus 63 is a promising biocontrol agent that could be used to combat the bacterial leaf blight diseases of rice.

Three phytotoxins produced by Neopestalotiopsis clavispora, the causal agent of ring spot on Kadsura coccinea

Phytotoxins are widely found in plant pathogens. In recent years, many diseases caused by Neopestalotiopsis clavispora have been reported. To better understand the pathogenicity of N. clavispora, a solid fermentation strategy was employed to isolate and identify virulence factors afritoxinone B, afritoxinone A and oxysporone. The phytotoxic activities of these toxins were evaluated. Oxysporone exhibited high levels of phytotoxic activity after 72 h and the lesion area ranged from 21.5-84.3 mm2 after 9 days of treatment. The phytotoxic activities of the other two compounds were lower than that for oxysporone. The phytotoxic activity towards non-host organisms was also assessed for the three analyzed compounds; phytotoxic activity was observed in each case. Based on these results, we conclude that oxysporone is the main virulence factor in N. clavispora. We also suggest that each of the three compounds were non-host-specific toxins (NHST). To our knowledge, this is the first study to analyze phytotoxins produced by N. clavispora.

Antibacterial and cytotoxic metabolites of termite-associated Streptomyces sp. BYF63

Four anthraquinone derivatives, termstrin A, B, C and D (1-4), were isolated and purified from termite-associated Streptomyces sp. BYF63. Their structures were elucidated on the basis of extensive spectroscopic analyses (HR-ESI-MS, 1D and 2D NMR). Compounds 1 and 4 were found to possess potent antibacterial activities against Staphylococcus aureus, with the zone of inhibition (ZOI) values of 12.85 and 11.17 mm, respectively, which were comparable to that of penicillin sodium with ZOI of 13.15 mm. Furthermore, metabolite 1 showed moderate cytotoxicities against melanoma cell line A375 and gastric cancer cell line MGC-803, with IC₅₀ values of 22.76 and 36.65 μM, respectively, which were less than those of referenced adriamycin.

Polyketide Derivatives from Mangrove Derived Endophytic Fungus Pseudopestalotiopsis theae

Chemical investigation of secondary metabolites from the endophytic fungus Pseudopestalotiopsis theae led to the isolation of eighteen new polyketide derivatives, pestalotheols I–Q (1–9) and cytosporins O–W (15–23), together with eight known analogs (10–14 and 24–26). The structures of the new compounds were elucidated by HRMS and 1D and 2D NMR data, as well as by comparison with literature data. Modified Mosher’s method was applied to determine the absolute configuration of some compounds. Compound 23 showed significant cytotoxicity against the mouse lymphoma cell line L5178Y with an IC₅₀ value of 3.0 μM. Furthermore, compounds 22 and 23 showed moderate antibacterial activity against drug-resistant Acinetobacter baumannii (ATCC BAA-1605) in combination with sublethal colistin concentrations.

Secondary Metabolites Produced by an Endophytic Fungus Pestalotiopsis microspora

An endophytic fungus Pestalotiopsis microspora isolated from the fruits of Manilkara zapota was cultured in potato dextrose broth media. Chromatographic separation of the EtOAc extract of the broth and mycelium led to the isolation of a new azaphilonoid named pitholide E (1), in addition to previously identified pitholide B (2), pitholide D (3), pestalotin (LL-P880α) (4), PC-2 (5), LL-P880β (6), tyrosol (7) and 4-oxo-4H-pyran-3-acetic acid (8). An endophytic fungus P. microspora from M. zapota and the isolation of compounds 1-5, 7 and 8 from P. microspora are reported here for the first time.

Benzannulated spiroketal natural products: isolation, biological activity, biosynthesis, and total synthesis

A review discussing the isolation, biological activity, biosynthesis, and total synthesis of naturally occurring benzannulated spiroketals.

Pestalotilide A, a New Cytotoxic Diphenyl Ether Derivative from Pestalotiposis guepinii

A new diphenyl ether derivative, named pestalotilide A (1), along with four known compounds (2-5) have been isolated from the organic extracts of an endophytic fungus Pestalotiposis guepinii. Their structures were elucidated on the basis of HR-ESI-MS, 1D and 2D NMR spectroscopic data analyses. These isolates were evaluated for cytotoxicity against three cancer cell lines: Hela, HCT116 and A549; pestalotilide A exhibited weak in vitro anti-proliferative activities against the tested cell lines, with IC50 values of 23.8, 18.4 and 35.2 μM, respectively.

Streptomyces amphotericinicus sp. nov., an amphotericin-producing actinomycete isolated from the head of an ant (Camponotus japonicus Mayr)

A novel actinomycete, designated strain 1H-SSA8^T, was isolated from the head of an ant (Camponotus japonicus Mayr) and was found to produce amphotericin. A polyphasic approach was employed to determine the status of strain 1H-SSA8^T. Morphological and chemotaxonomic characteristics were consistent with those of members of the genus Streptomyces. The menaquinones detected were MK-9(H6), MK-9(H8) and MK-9(H4). The phospholipid profile consisted of diphosphatidylglycerol, phosphatidylmethylethanolamine, phosphatidylethanolamine and phosphatidylinositol mannoside. The major fatty acids were identified as iso-C16 : 0, C16 : 0, C15 : 0 and anteiso-C15 : 0. Analysis of the 16S rRNA gene sequence showed that strain 1H-SSA8^T belongs to the genus Streptomyces with high sequence similarity to Streptomyces ramulosus NRRL B-2714^T (99.2 %). Two tree-making algorithms based on 16S rRNA gene sequences showed that the isolate formed a phyletic line with Streptomyces himastatinicus ATCC 53653^T (98.7 %). The MLSA utilizing partial sequences of the housekeeping genes (atpD, gyrB, recA, rpoB and trpB) also supported the position. However, evolutionary distances were higher than the 0.007 MLSA evolutionary distance threshold proposed for species-level relatedness. Moreover, the low level of DNA-DNA relatedness and phenotypic differences allowed the novel isolate to be differentiated from its most closely related strain S. ramulosus NRRL B-2714^T and strain S. himastatinicus ATCC 53653^T. It is concluded that the organism can be classified as representing a novel species of the genus Streptomyces, for which the name Streptomyces amphotericinicus sp. nov. is proposed. The type strain is 1H-SSA8^T (=CGMCC 4.7350^T=DSM 103128^T).

Diversity, Bacterial Symbionts and Antibacterial Potential of Gut-Associated Fungi Isolated from the Pantala flavescens Larvae in China

The diversity of fungi associated with the gut of Pantala flavescens larvae was investigated using a culture-dependent method and molecular identification based on an analysis of the internally transcribed spacer sequence. In total, 48 fungal isolates were obtained from P. flavescens larvae. Based on phylogenetic analyses, the fungal isolates were grouped in 5 classes and 12 different genera. Fourteen bacterial 16S rDNA sequences derived from total genomic DNA extractions of fungal mycelia were obtained. The majority of the sequences were associated with Proteobacteria (13/14), and one Bacillaceae (1/14) was included. Leclercia sp., Oceanobacillus oncorhynchi and Methylobacterium extorquens, were reported for the first time as bacterial endosymbionts in fungi. High-performance liquid chromatography (HPLC) analysis indicated that bacterial symbionts produced specific metabolites and also exerted an inhibitory effect on fungal metabolites. The biological activity of the fungal culture extracts against the pathogenic bacteria Staphylococcus aureus (ATCC 6538), Bacillus subtilis (ATCC 6633) and Escherichia coli (ATCC 8739) was investigated, and 20 extracts (42%) exhibited antibacterial activity against at least one of the tested bacterial strains. This study is the first report on the diversity and antibacterial activity of symbiotic fungi residing in the gut of P. flavescens larvae, and the results show that these fungi are highly diverse and could be exploited as a potential source of bioactive compounds.

Antibacterial epipolythiodioxopiperazine and unprecedented sesquiterpene from Pseudallescheria boydii, a beetle (coleoptera)-associated fungus

Pseudallescheria boydiiproduces four new epipolythiodioxopiperazine (ETP) boydines A–D and two novel sesquiterpene boydenes A and B.

Antifungal activities of metabolites produced by a termite-associated Streptomyces canus BYB02

Two main antifungal metabolites resistomycin and tetracenomycin D were isolated and purified from a termite-associated Streptomyces canus BYB02 by column chromatography. The structures of isolated compounds were determined on the basis of extensive spectroscopic analysis. Resistomycin possessed strong activities against mycelial growth of Valsa mali (IC(50) = 1.1 μg/mL) and Magnaporthe grisea (IC(50) = 3.8 μg/mL), which were comparable to those of referenced cycloheximide, with IC(50) values of 2.3 and 0.3 μg/mL, respectively. A further spore germination test showed that resistomycin exhibited potent reduction in spore germination for M. grisea , with an IC(50) value of 5.55 μg/mL. Finally, the in vivo antifungal activity experiment showed that resistomycin possessed significant preventive efficacy against rice blast, which was more potent than that of referenced carbendazim, with control efficacies of 66.8 and 58.7%, respectively. The present results suggest that resistomycin has potential to be used as a fungicide.

Afritoxinones A and B, dihydrofuropyran-2-ones produced by Diplodia africana the causal agent of branch dieback on Juniperus phoenicea

Two phytotoxic dihydrofuropyran-2-ones, named afritoxinones A and B, were isolated from liquid culture of Diplodia africana, a fungal pathogen responsible for branch dieback of Phoenicean juniper in Italy. Additionally, six others known metabolites were isolated and characterized: oxysporone, sphaeropsidin A, epi-sphaeropsidone, R-(-)-mellein, (3R,4R)-4-hydroxymellein and (3R,4S)-4-hydroxymellein. The structures of afritoxinones A and B were established by spectroscopic and optical methods and determined to be as (3aS(*),6R(*),7aS)-6-methoxy-3a,7a-dihydro-3H,6H-furo[2,3-b]pyran-2-one and (3aR(*),6R(*),7aS)-6-methoxy-3a,7a-dihydro-3H,6H-furo[2,3-b]pyran-2-one, respectively. The phytotoxic activity of afritoxinones A and B and oxysporone was evaluated on host (Phoenicean juniper) and non-host plant (holm oak, cork oak and tomato) by cutting and leaf puncture assay. Oxysporone proved to be the most phytotoxic compound. This study represents the first report of secondary metabolites produced by D. africana. In addition, the taxonomic implications of secondary metabolites in Botryosphaeriaceae family studies are discussed.

Dihydroberkleasmin A: a new eremophilane sesquiterpenoid from the fermentation broth of the plant endophytic fungus Pestalotiopsis photiniae

Dihydroberkleasmin A (1), a new ester-substituted sesquiterpenoid related to the eremophilane class, together with the known compound berkleasmin C (2), were isolated from the fermentation broth of the plant endophytic fungus Pestalotiopsis photiniae. The structure of dihydroberkleasmin A (1) was elucidated by extensive spectroscopic analysis. The stereochemistry was assigned by comparison of the NMR spectroscopic data with those of berkleasmin A.

Phytotoxic and antifungal metabolites from Curvularia sp. FH01 isolated from the gut of Atractomorpha sinensis

Two main phytotoxic and antifungal phthalic acid butyl isobutyl ester (1) and radicinin (2) were isolated from the culture of Curvularia sp. FH01, a fungus residing in the Atractomorpha sinensis gut. The structures of isolated metabolites were established on the basis of spectral analysis. Metabolites 1 and 2 exhibited significant phytotoxic activity against the radical growth of Echinochloa crusgalli with their IC(50) values of 61.9 and 5.9 μg/mL, respectively, which were comparable to that 2,4-dichlorophenoxyacetic acid (2.0 μg/mL) used as a positive control. The antifungal test results showed that compound 2 possessed strong antifungal activity against Magnaporthe grisea (IC(50)=16.3 μg/mL) and Valsa mali (IC(50)=18.2 μg/mL). The findings of the present study suggest that bioactive properties of the fungus FH01 can be attributed to its major components, phthalic acid butyl isobutyl ester and radicinin, and both agents have a potential to be used as herbicide and fungicide.