New nematicidal and antimicrobial secondary metabolites from a new species in the new genus, Pseudobambusicola thailandica

Isolation, Identification and Molecular Mechanism Analysis of the Nematicidal Compound Spectinabilin from Newly Isolated Streptomyces sp. DT10

Plant parasitic nematodes (PPNs) are highly destructive and difficult to control, while conventional chemical nematicides are highly toxic and cause serious environmental pollution. Additionally, resistance to existing pesticides is becoming increasingly common. Biological control is the most promising method for the controlling of PPNs. Therefore, the screening of nematicidal microbial resources and the identification of natural products are of great significance and urgency for the environmentally friendly control of PPNs. In this study, the DT10 strain was isolated from wild moss samples and identified as Streptomyces sp. by morphological and molecular analysis. Using Caenorhabditis elegans as a model, the extract of DT10 was screened for nematicidal activity, which elicited 100% lethality. The active compound was isolated from the extracts of strain DT10 using silica gel column chromatography and semipreparative high-performance liquid chromatography (HPLC). The compound was identified as spectinabilin (chemical formula C28H31O6N) using liquid chromatography mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR). Spectinabilin exhibited a good nematicidal activity on C. elegans L1 worms, with a half-maximal inhibitory concentration (IC50) of 2.948 μg/mL at 24 h. The locomotive ability of C. elegans L4 worms was significantly reduced when treated with 40 μg/mL spectinabilin. Further analysis of spectinabilin against known nematicidal drug target genes in C. elegans showed that it acts via target(s) different from those of some currently used nematicidal drugs such as avermectin and phosphine thiazole. This is the first report on the nematicidal activity of spectinabilin on C. elegans and the southern root-knot nematode Meloidogyne incognita. These findings may pave the way for further research and application of spectinabilin as a potential biological nematicide.

Natural nematicidal metabolites and advances in their biocontrol capacity on plant parasitic nematodes

Covering: 2010 to 2021Natural nematicidal metabolites are important sources of nematode control. This review covers the isolation and structural determination of nematicidal metabolites from 2010 to 2021. We summarise chemical structures, bioactivity, metabolic regulation and biosynthesis of potential nematocides, and structure-activity relationship and application potentiality of natural metabolites in plant parasitic nematodes' biocontrol. In doing so, we aim to provide a comprehensive overview of the potential roles that natural metabolites can play in anti-nematode strategies.

The Fight against Plant-Parasitic Nematodes: Current Status of Bacterial and Fungal Biocontrol Agents

Plant-parasitic nematodes (PPNs) are among the most notorious and underrated threats to food security and plant health worldwide, compromising crop yields and causing billions of dollars of losses annually. Chemical control strategies rely heavily on synthetic chemical nematicides to reduce PPN population densities, but their use is being progressively restricted due to environmental and human health concerns, so alternative control methods are urgently needed. Here, we review the potential of bacterial and fungal agents to suppress the most important PPNs, namely Aphelenchoides besseyi, Bursaphelenchus xylophilus, Ditylenchus dipsaci, Globodera spp., Heterodera spp., Meloidogyne spp., Nacobbus aberrans, Pratylenchus spp., Radopholus similis, Rotylenchulus reniformis, and Xiphinema index.

Morpho-Phylogenetic Evidence Reveals Novel Pleosporalean Taxa from Sichuan Province, China

Pleosporales is the largest and most morphologically diverse order in Dothideomycetes, including a large proportion of saprobic fungi. During the investigation of microfungi from decaying wood in Sichuan Province, several novel fungal taxa of asexual and sexual morphs were collected, identified, and well-described. Phylogenetic analyses based on SSU, ITS, LSU, RPB2 and TEF1α gene sequences suggested that these new taxa were related to Pleosporales and distributed in five families, viz. Amorosiaceae, Bambusicolaceae, Lophiostomataceae, Occultibambusaceae and Tetraplosphaeriaceae. The morphological comparison and molecular phylogeny evidence justify the establishment of six new taxa, namely Bambusicola guttulata sp. nov., Flabellascoma sichuanense sp. nov., Neoangustimassarina sichuanensis gen. et sp. nov., Occultibambusa sichuanensis sp. nov. and Pseudotetraploa bambusicola sp. nov. Among them, Neoangustimassarina was introduced as the second sexual morph genus in Amorosiaceae; Bambusicola guttulata, O. sichuanensis and P. bambusicola were isolated from bamboos, which contributed to the diversity of bambusicolous fungi. The detailed, illustrated descriptions and notes for each new taxon are provided, as well as a brief note for each family. The potential richness of fungal diversity in Sichuan Province is also discussed.

Insight into the Taxonomic Resolution of the Pleosporalean Species Associated with Dead Woody Litter in Natural Forests from Yunnan, China

In the course of investigating the systematics of woody litter micromycete associates in Yunnan Province, China, we found one new species in Phaeoseptaceae, one new genus and three new species in Sulcatisporaceae from 16 specimens collected (ten collections of ascomycetous teleomorphs, four collections of hyphomycetous and two collections of coelomycetes anamorphs) from Ailaoshan, Chuxiong, Diqing, Honghe, Kunming, Lancang, Mengla and Yuxi in Yunnan Province. These taxonomic novelties were recognized with the aid of morphological comparisons and phylogenetic analyses of multiple gene sequences (non-translated loci and protein-coding regions). Pleopunctum menglaense sp. nov. is accommodated in Phaeoseptaceae (Pleosporales) based on its hyphomycetous anamorph, which is characterized by superficial sporodochia on the host surface, macronematous, mononematous, cylindrical, unbranched, aseptate, hyaline and smooth-walled conidiophores, monoblastic, terminal, hyaline conidiogenous cells, hyaline, muriform α conidia, and brown, muriform β conidia with tri-lobed wing like basal cells. Kazuakitanaka gen. nov. (type: K. yuxiensis) is introduced in Sulcatisporaceae (Massarineae, Pleosporales) for a saprobic ascomycete with teleomorphic and anamorphic (coelomycetous) features. The teleomorph possesses globose to subglobose ascomata with acentric ostiole, a peridial wall of textura angularis to textura prismatica, cylindric-clavate, pedicellate asci with an ocular chamber, and 1–2-septate, hyaline, fusiform, guttulate ascospores with a distinct mucilaginous sheath. The anamorph features pycnidial conidiomata, phialidic, ampulliform to cylindrical, hyaline conidiogenous cells and ampulliform to cylindrical, one-to-three-septate, hyaline, guttulate conidia. Loculosulcatispora was known only from its anamorph of L. thailandica. We observed the teleomorph of Loculosulcatispora hongheensis sp. nov. and amended the generic description of Loculosulcatispora accordingly. Loculosulcatispora hongheensis is characterized by globose to subglobose ascomata with a central ostiole, a peridial wall of textura angularis to globosa, branched, septate, pseudoparaphyses, clavate asci with a short pedicel and a minute ocular chamber and hyaline, fusiform, 1-septate ascospores with a thick irregular mucilaginous sheath. This study provides some insights into the diversity of fungi on dead woody litter in terrestrial habitats.

Polyketide-Derived Secondary Metabolites from a Dothideomycetes Fungus, Pseudopalawania siamensisgen. et sp. nov., (Muyocopronales) with Antimicrobial and Cytotoxic Activities

Pseudopalawania siamensisgen. et sp. nov., from northern Thailand, is introduced based on multi-gene analyses and morphological comparison. An isolate was fermented in yeast malt culture broth and explored for its secondary metabolite production. Chromatographic purification of the crude ethyl acetate (broth) extract yielded four tetrahydroxanthones comprised of a new heterodimeric bistetrahydroxanthone, pseudopalawanone (1), two known dimeric derivatives, 4,4'-secalonic acid D (2) and penicillixanthone A (3), the corresponding monomeric tetrahydroxanthone paecilin B (4), and the known benzophenone, cephalanone F (5). Compounds 1-3 showed potent inhibitory activity against Gram-positive bacteria. Compounds 2 and 3 were inhibitory against Bacillus subtilis with minimum inhibitory concentrations (MIC) of 1.0 and 4.2 μg/mL, respectively. Only compound 2 showed activity against Mycobacterium smegmatis. In addition, the dimeric compounds 1-3 also showed moderate cytotoxic effects on HeLa and mouse fibroblast cell lines, which makes them less attractive as candidates for development of selectively acting antibiotics.

Metabolites of a Drechslera sp. endophyte with potential as biocontrol and bioremediation agent

Endophytic fungi have several well-established beneficial effects on plant health and growth, and are a huge source of bioactive compounds. The endophyte Drechslera sp. strain 678, isolated from the roots of an Australian native grass Neurachne alopecuroidea, demonstrated efficacy against four plant pathogens (Pythium ultimum, Rhizoctonia solani, Botrytis cinerea, Alternaria alternata). In addition, strain 678 was capable of degrading a common additive used in gasoline, known as methyl tertiary-butyl ether (MtBE). Thus, the organic extracts obtained from the culture filtrate of strain 678 were studied. Metabolomic analysis revealed the presence of two major bioactive metabolites, monocerin and an alkynyl substituted epoxycyclohexenone derivative, which showed good antifungal activity. The Drechslera sp. strain 678 and its compounds show promise for applications in biocontrol and bioremediation activities in agriculture or as a remediation option for MtBE contamination in soil.

Identification of Rosellinia species as producers of cyclodepsipeptide PF1022 A and resurrection of the genus Dematophora as inferred from polythetic taxonomy

Rosellinia (Xylariaceae) is a large, cosmopolitan genus comprising over 130 species that have been defined based mainly on the morphology of their sexual morphs. The genus comprises both lignicolous and saprotrophic species that are frequently isolated as endophytes from healthy host plants, and important plant pathogens. In order to evaluate the utility of molecular phylogeny and secondary metabolite profiling to achieve a better basis for their classification, a set of strains was selected for a multi-locus phylogeny inferred from a combination of the sequences of the internal transcribed spacer region (ITS), the large subunit (LSU) of the nuclear rDNA, beta-tubulin (TUB2) and the second largest subunit of the RNA polymerase II (RPB2). Concurrently, various strains were surveyed for production of secondary metabolites. Metabolite profiling relied on methods with high performance liquid chromatography with diode array and mass spectrometric detection (HPLC-DAD/MS) as well as preparative isolation of the major components after re-fermentation followed by structure elucidation using nuclear magnetic resonance (NMR) spectroscopy and high resolution mass spectrometry (HR-MS). Two new and nine known isopimarane diterpenoids were identified during our mycochemical studies of two selected Dematophora strains and the metabolites were tested for biological activity. In addition, the nematicidal cyclodepsipeptide PF1022 A was purified and identified from a culture of Rosellinia corticium, which is the first time that this endophyte-derived drug precursor has been identified unambiguously from an ascospore-derived isolate of a Rosellinia species. While the results of this first HPLC profiling were largely inconclusive regarding the utility of secondary metabolites as genus-specific chemotaxonomic markers, the phylogeny clearly showed that species featuring a dematophora-like asexual morph were included in a well-defined clade, for which the genus Dematophora is resurrected. Dematophora now comprises all previously known important plant pathogens in the genus such as D. arcuata, D. bunodes, D. necatrix and D. pepo, while Rosellinia s. str. comprises those species that are known to have a geniculosporium-like or nodulisporium-like asexual morph, or where the asexual morph remains unknown. The extensive morphological studies of L.E. Petrini served as a basis to transfer several further species from Rosellinia to Dematophora, based on the morphology of their asexual morphs. However, most species of Rosellinia and allies still need to be recollected in fresh state, cultured, and studied for their morphology and their phylogenetic affinities before the infrageneric relationships can be clarified.

Skeletocutins M-Q: biologically active compounds from the fruiting bodies of the basidiomycete Skeletocutis sp. collected in Africa

During the course of screening for new metabolites from basidiomycetes, we isolated and characterized five previously undescribed secondary metabolites, skeletocutins M-Q (1-5), along with the known metabolite tyromycin A (6) from the fruiting bodies of the polypore Skeletocutis sp. The new compounds did not exhibit any antimicrobial, cytotoxic, or nematicidal activities. However, compound 3 moderately inhibited the biofilm formation of Staphylococcus aureus (S. aureus), while compounds 3 and 4 performed moderately in the ʟ-leucine-7-amido-4-methylcoumarin (ʟ-Leu-AMC) inhibition assay. These compounds represent the first secondary metabolites reported to occur in the fruiting bodies by Skeletocutis. Interestingly, tyromycin A (6) was found to be the only common metabolite in fruiting bodies and mycelial cultures of the fungus, and none of the recently reported skeletocutins from the culture of the same strain were detected in the basidiomes.

Skeletocutins A-L: Antibacterial Agents from the Kenyan Wood-Inhabiting Basidiomycete, Skeletocutis sp

Fermentation of the fungal strain Skeletocutis sp. originating from Mount Elgon Natural Reserve in Kenya, followed by bioassay guided fractionation led to the isolation of 12 previously undescribed metabolites named skeletocutins A-L (1-5 and 7-13) together with the known tyromycin A (6). Their structures were assigned by NMR spectroscopy complemented by HR-ESIMS. Compounds 1-6 and 11-13 exhibited selective activities against Gram-positive bacteria, while compound 10 weakly inhibited the formation of biofilm of Staphylococcus aureus. The isolated metabolites were also evaluated for inhibition of _L-leucine aminopeptidase, since tyromycin A had previously been reported to possess such activities but only showed weak effects. Furthermore, all compounds were tested for antiviral activity against Hepatitis C virus (HCV), and compound 6 moderately inhibited HCV infectivity with an IC₅₀ of 6.6 μM.

Kenalactams A-E, Polyene Macrolactams Isolated from Nocardiopsis CG3

In our screening program for new biologically active secondary metabolites, a new strain, Nocardiopsis CG3 (DSM 106572), isolated from the saltpan of Kenadsa, was found to produce five new polyene macrolactams, the kenalactams A-E (1-5). Their structures were elucidated by spectral methods (NMR and HRESIMS), and the absolute configuration was derived by chemical derivatization (Mosher's method). Through a feeding experiment, alanine was proven to be the nitrogen-bearing starter unit involved in biosynthesis of the polyketide kenalactam A (1). Kenalactam E (5) was cytotoxic against human prostate cancer PC-3 cells with an IC₅₀ value of 2.1 μM.

Sesquiterpenes from an Eastern African Medicinal Mushroom Belonging to the Genus Sanghuangporus

During the course of searching for new anti-infective and other biologically active secondary metabolites from Kenyan basidiomycetes, 13 previously undescribed metabolites, (6 R,7 S,10 R)-7,10-epoxy-7,11-dimethyldodec-1-ene-6,11-diol (1) and 12 sesquiterpenes named elgonenes A-L (2-13), and the known compound P-coumaric acid (14) were isolated from a basidiomycete collected in Mount Elgon Natural Reserve. The producing organism represents a new species of the genus Sanghuangporus, which is one of the segregates of the important traditional Asian medicinal mushrooms that were formerly known as the " Inonotus linteus" complex. The structure elucidation of compounds 1-13, based on 2D NMR spectroscopy, high-resolution mass spectrometry, and other spectral methods, and their antibacterial, antifungal, and cytotoxic activities are reported.

Nematicidal anthranilic acid derivatives from Laccaria species

Three undescribed natural products, the anthranilic acid derivatives laccanthrilic acids A, B, and C, as well as the known (3S)-1,2,3,4-tetrahydro-3-β-carboline-3-carboxylic acid were isolated from fruiting bodies of Laccaria laccata. The structures were established by 1D and 2D NMR spectroscopy, HR-(+)-ESIMS and chemical synthesis. The absolute configuration of laccanthrilic acids A and B was determined by GC-MS after hydrolytic cleavage and derivatisation of the resulting glutamic acid with methanol and Mosher's reagent and subsequent comparison with authentic synthetic samples of known absolute configuration. The absolute configuration of laccanthrilic acid C was determined by comparison of the CD spectra of laccanthrilic acids B and C with each other. Metabolic profiling of related species showed that the compounds are common in the genus Laccaria. Laccanthrilic acid B exhibited moderate nematicidal effects against Caenorhabditis elegans, which might explain to some degree the beneficial role of these fungi for the growth and survival of their host plants.

Cytotoxic, antimicrobial and antiviral secondary metabolites produced by the plant pathogenic fungus Cytospora sp. CCTU A309

Chemical analysis of extracts from cultures of the plant pathogenic fungus Cytospora sp. strain CCTU A309 collected in Iran led to the isolation of two previously unreported heptanedioic acid derivatives namely (2R,3S) 2-hydroxy-3-phenyl-4-oxoheptanedioic acid (1) and (2S,3S) 2-hydroxy-3-phenyl-4-oxoheptanedioic acid (2) as diastereomers, four previously undescribed prenylated p-terphenyl quinones 3-6 in addition to five known metabolites. Their structures were elucidated on the basis of extensive spectroscopic analysis and high-resolution mass spectrometry. For metabolites 1 and 2, the absolute configurations at C-2 were deduced from comparison of the ¹H NMR difference of their (S)- and (R)-phenylglycine methyl ester derivatives while the relative configurations were tentatively assigned by a J-based analysis and confirmed by comparison of ¹³C chemical shifts to literature data. The isolated compounds were tested for their cytotoxic, antimicrobial (including biofilm inhibition), antiviral, and nematicidal activities. While only moderate antimicrobial effects were observed, the terphenyl quinone derivatives 3-6 and leucomelone (10) exhibited significant cytotoxicity against the mouse fibroblast L929 and cervix carcinoma KB-3-1 cell lines with IC₅₀ values ranging from 2.4 to 26 μg/mL. Furthermore, metabolites 4-6 showed interesting antiviral activity against hepatitis C virus (HCV).

Nematicidal Cyclic Lipodepsipeptides and a Xanthocillin Derivative from a Phaeosphariaceous Fungus Parasitizing Eggs of the Plant Parasitic Nematode Heterodera filipjevi

The new cyclic lipodepsipeptide ophiotine (1), two new arthrichitin derivatives named arthrichitins B (4) and C (5), a new xanthocillin-like alkaloid, xanthomide Z (2), and the previously described arthrichitin (3) were isolated from the liquid culture broth of a nematode-associated fungus with affinities to the genus Ophiosphaerella. The structural elucidation and determination of the absolute configuration of the new molecules were accomplished using a combination of spectroscopic and chemical techniques, including 1D and 2D NMR, HRMS, and Marfey's analysis. Opiotine (1) displayed moderate nematicidal activity against the host nematode ( Heterodera filipjevi), while xanthomide Z (2) exhibited very weak activity. Arthrichitin C (5) showed very weak cytotoxic effects on several cancer cell lines, with IC₅₀ values in the range of 24-33 μM. Xanthomide Z is among few xanthocillin derivatives that comprise formamide functions instead of the cyano functions that are usually observed in this class of fungal alkaloids.