Search Results (57)

As a staple food, potato (Solanum tuberosum L.) (Solanaceae) is one of the most produced food crops to ensure food security. The potato tuber moth (PTM), Phthorimaea operculella (Zeller, 1873) (Lepidoptera: Gelechiidae), is a major pest of potato, damaging both the growing and storage processes. In recent years, green pest control strategies have been gaining importance to reduce the adverse effects of chemicals and protect the environment. Entomopathogenic nematodes (EPNs) and their bacterial endosymbionts (Xenorhabdus and Photorhabdus spp.) have been one of the top topics studied in sustainable pest control approaches. In the present study, the two most common EPN species, Steinernema feltiae and Heterorhabditis bacteriophora, and their bacterial associates, Xenorhabdus bovienii and Photorhabdus luminescens subsp. kayaii were evaluated against PTM larvae separately and in combination with spinosad. The survival rates of infective juveniles (IJs) of EPNs were over 92% after 72 h of direct exposure to spinosad. Co-application of EPNs and bioactive compounds (BACs) of endosymbiotic bacteria with spinosad induced synergistic interactions and achieved the maximum mortality (100%) in PTM larvae 48 h post-treatment. Spinosad and BAC combinations were highly efficient in controlling the PTM larvae and provided LT₅₀ values below 23.0 h. Gas chromatography mass spectrometry (GC-MS) analysis identified 29 compounds in total, 20 of which belonged to P. luminescens subsp. kayaii. The results indicate that the integration of EPNs and BACs of endosymbiotic bacteria with spinosad presents a synergistic interaction and enhances pest control efficacy. Full article

Photorhabdus and Xenorhabdus bacteria, members of the Morganellaceae family, are sources of novel natural products for the biocontrol of fungal pathogens in soybean production. This study demonstrated the inhibitory effects of metabolites from four Photorhabdus and Xenorhabdus strains (including a local isolate, X. szentirmaii PAM 25), against four key phytopathogenic fungi. Bacterial metabolite efficacy and fungal susceptibility varied. Xenorhabdus szentirmaii DSM 16338, X. szentirmaii PAM 25, and X. doucetiae demonstrated significant inhibition (>90%) against Sclerotinia sclerotiorum, Botrytis cinerea, and Macrophomina phaseolina, exhibiting superior efficacy compared to X. nematophila and Photorhabdus kayaii. Fusarium oxysporum demonstrated greater resistance to the bacterial supernatants. We identified fabclavine, pyrollizixenamide, and szentirazine from X. szentirmaii, and xenocoumacins from X. doucetiae as the antifungal bioactive compounds in the respective easyPACid mutants. Furthermore, we assessed the efficacy of X. szentirmaii PAM 25 and its metabolites in protecting soybean seeds from S. sclerotiorum and investigated the shelf stability of the bacterial metabolites as the fungus suppressors. Cell-free supernatant maintained >80% inhibition of S. sclerotiorum after one year at 5–35 °C. Importantly, the cell-free supernatant, as well as the bacterial culture, effectively inhibited S. sclerotiorum in seed treatments, ensuring ≥80% seed germination, comparable to thiophanate-methyl + fluazinam fungicide. This study demonstrates that the direct seed application of Xenorhabdus and Photorhabdus bacteria offers a practical and innovative biological control method against soil-borne fungal pathogens. Full article

Xenorhabdus species are entomopathogenic bacteria that live in symbiosis with Steinernema nematodes and produce a wide range of bioactive secondary metabolites. This study aimed to characterize the complete genomes and biosynthetic potential of two novel Xenorhabdus isolates, ALN7.1 and ALN11.5, recovered from Steinernema lamjungense collected in Northern Thailand. High-quality genome assemblies were generated, and phylogenomic comparisons confirmed that both isolates belonged to the recently described species Xenorhabdus thailandensis. The assembled genomes were approximately 4.02 Mb in size, each comprising a single circular chromosome with a GC content of 44.6% and encoding ~3800 protein-coding sequences, consistent with the features observed in other members of the genus. Biosynthetic gene cluster (BGCs) prediction using antiSMASH identified 19 BGCs in ALN7.1 and 18 in ALN11.5, including known clusters for holomycin, pyrrolizixenamide, hydrogen cyanide, and gamexpeptide C, along with several uncharacterized clusters, suggesting unexplored metabolic potential. Comparative analyses highlighted conserved yet strain-specific BGC profiles, indicating possible diversification within the species. These results provide genomic insights into X. thailandensis ALN7.1 and ALN11.5 and support their potential as valuable sources for the discovery of novel natural products and for future biotechnological applications. Full article

The black-spotted frog (Pelophylax nigromaculatus) is a common economic species in the rice–frog ecological cropping mode. The present study investigated microbial community structures in paddy water and black-spotted frog’s guts across rice monoculture and low-/high-density rice–frog co-cropping systems at four rice growth stages. Proteobacteria dominate in paddy water, while frog guts are enriched in Firmicutes and Actinobacteriota. The frog density shows no impact on the α-diversity, but rice growth stages significantly alter the Shannon, Simpson, and Pielou_e indices (p < 0.01). Co-cropping may promote amino acid synthesis, elemental cycling, and stress tolerance in paddy water microbiota, which are more diverse than gut microbiota. Strong correlations exist between paddy water and gut microbiotas, with Limnohabitans being linked to gut diversity (p < 0.05). Low-density co-cropping enhances Xenorhabdus, which is beneficial for pest control and stabilizes gut microbiota. The results of this study offer insights for managing rice–frog systems based on rice growth stages. Full article

Xenorhabdus nematophila has excellent potential for application in both medicine and agriculture due to its various active secondary metabolites. The transcriptional regulator OmpR negatively regulates Xenocoumacin 1 (Xcn1), which has wide antimicrobial activity. Here, we expressed and purified OmpR and verified its binding activities to promoters via an electrophoretic mobility shift assay. RNA sequencing was used to analyze the relevance and difference of differentially expressed genes between X. nematophila and its mutant ΔompR. Compared with the WT, 1127 differentially expressed genes were found in ΔompR, while 4150 co-expressed genes were detected. RT-qPCR data validated the RNA-seq results with 20 randomly selected genes. OmpR positively regulates the process of porphyrin metabolism, quorum sensing, β-Lactam resistance and glyoxylate and dicarboxylate metabolism, while negatively regulating the phosphotransferase system, two-component system and bacterial chemotaxis. OmpR indirectly regulates the biosynthesis of Xcn1 by positively regulating the process of glyoxylate metabolism, which consumes energy and precursors, and negatively regulates biomacromolecules biosynthesis, which provides energy and precursors. Overall, this work revealed the indirect effects of OmpR on the biosynthesis of Xcn1, serving as a foundation for future research into the intricate regulatory network of X. nematophila. Full article

Drosophila melanogaster is broadly used to model host–pathogen interactions. Entomopathogenic nematodes are excellent research tools for dissecting the molecular and functional basis of parasitism and the host’s anti-parasitic response. In this work, we used discovery metabolomics to explore the differences in the metabolome composition of wild type D. melanogaster larvae that were infected with symbiotic nematodes (Steinernema carpocapsae carrying Xenorhabdus nematophila mutualistic bacteria) or axenic nematodes (S. carpocapsae lacking their bacterial partners). Benefiting from their high separation power, sensitivity, and compatibility with low amounts of the starting metabolome, we leveraged microanalytical capillary electrophoresis electrospray ionization mass spectrometry (CE-ESI-MS) to profile the small (<500 Da) polar portion of the metabolome among these experimental treatments. We detected and quantified 122 different small molecules, of which 50 were identified with high confidence. Supervised multivariate analysis revealed that the infection was paralleled with changes in amino acid biosynthesis (arginine, phenylalanine, tryptophan, and tyrosine), metabolism (alanine, arginine, aspartate, glutamate, glycine, proline, serine, and threonine), and classical signalling (aspartate, γ-aminobutyrate, glutamate, and pyridoxine). This study demonstrates the ability of high-sensitivity CE-ESI-MS to uncover metabolic perturbations during infection. The results from the metadata may facilitate the design of targeted studies to explore small biomolecules and their functions during host–pathogen interaction. Full article

Heat shock proteins (HSPs), particularly HSP90, play a vital role in insect responses to environmental and biotic stresses by maintaining protein stability and supporting immune defenses. This study explores HSP90 regulation in Galleria mellonella larvae following exposure to the nematode Steinernema carpocapsae and its symbiotic bacterium Xenorhabdus nematophila. Exposure to live nematodes caused slight changes in HSP90 expression, while non-viable nematodes had no effect, suggesting that nematode secretions or symbiotic bacteria do not directly influence HSP90 levels. However, nematodes with altered surface properties significantly increased HSP90 expression. X. nematophila also moderately elevated HSP90 levels but this effect disappeared when weakly bound surface proteins were removed. Interestingly, under thermal stress, live nematodes reduced heat-induced HSP90 expression, whereas surface-treated nematodes enhanced it. These findings suggest that HSP90 modulation is influenced by biological control agents, highlighting a potential link between HSP90 and immune detection of invaders. This interaction may be crucial in adapting biological control strategies in response to climate change. Further research is needed to clarify HSP activation pathways, host immune interactions, and mechanisms of entomopathogen immune evasion, particularly under varying environmental temperatures, to enhance bioinsecticide efficacy. Full article

ABC toxin complexes (Tcs) are tripartite complexes that come together to form nano-syringe-like translocation systems. ABC Tcs are often compared with Bacillus thuringiensis (Bt) toxins, and as such, they have been highly studied as a potential novel pesticide to combat growing insect resistance. Moreover, it is possible to substitute the cytotoxic hypervariable region with alternative peptides, which promise potential use as a novel peptide delivery system. These toxins possess the unique ability to form active chimeric holotoxins across species and display the capability to translocate a variety of payloads across membrane bilayers. Additionally, mutagenesis on the linker region and the receptor binding domains (RBDs) show that mutations do not inherently cause a loss of functionality for translocation. For these reasons, Tcs have emerged as an ideal candidate for targeted protein engineering. However, elucidation of the specific function of each RBD in relation to target receptor recognition currently limits the use of a rational design approach with any ABC Tc. Additionally, there is a distinct lack of targeting and biodistribution data for many Tcs among mammals and mammalian cell lines. Here, we outline two separate strategies for modifying the targeting capabilities of the A subunit (TcA) from Xenorhabdus nematophilus, Xn-XptA2. We identify novel structural differences that make Xn-XptA2 different than other characterized TcAs and display the modular capabilities of substituting RBDs from alternative TcAs into the Xn-XptA2 scaffold. Finally, we show the first, to our knowledge, biodistribution data of any TcA in mice. Full article

Xenorhabdus and Photorhabdus bacteria, which live in mutualistic symbiosis with entomopathogenic nematodes, are currently recognised as an important source of bioactive compounds. During their extraordinary life cycle, these bacteria are capable of fine regulation of mutualism and pathogenesis towards two different hosts, a nematode and a wide range of insect species, respectively. Consequently, survival in a specific ecological niche favours the richness of biosynthetic gene clusters and respective metabolites with a specific structure and function, providing templates for uncovering new agrochemicals and therapeutics. To date, numerous studies have been published on the genetic ability of Xenorhabdus and Photorhabdus bacteria to produce biosynthetic novelty as well as distinctive classes of their metabolites with their activity and mechanism of action. Research shows diverse techniques and approaches that can lead to the discovery of new natural products, such as extract-based analysis, genetic engineering, and genomics linked with metabolomics. Importantly, the exploration of members of the Xenorhabdus and Photorhabdus genera has led to encouraging developments in compounds that exhibit pharmaceutically important properties, including antibiotics that act against Gram- bacteria, which are extremely difficult to find. This article focuses on recent advances in the discovery of natural products derived from these nematophilic bacteria, with special attention paid to new valuable leads for therapeutics. Full article

Entomopathogenic bacteria, classified into the genus Xenorhabdus, exhibit a dual lifestyle as mutualistic symbionts to Steinernema nematodes and as pathogens to a broad range of insects. Bacterial virulence depends on toxin proteins that induce toxemia and various immunosuppressive secondary metabolites that cause septicemia. Particularly, the immunosuppressive properties of Xenorhabdus bacteria determine the variability of their insecticidal activities. This study explored the role of peptide metabolites in virulence and its variation among six bacterial strains across three species: X. nematophila, X. bovienii, and X. hominickii. Initially, their virulence significantly varied against a susceptible lepidopteran host, Maruca vitrata, but showed less variation against a tolerant coleopteran host, Tenebrio molitor, with high median lethal bacterial doses. In M. vitrata, virulence was strongly correlated with bacterial growth rate and inhibitory activity against phospholipase A₂. Secondly, the six strains differed in the compositions of their secreted secondary metabolites, analyzed by GC-MS following ethyl acetate extraction. Notably, there was significant variation in the production of di- or tetra-peptides. Highly virulent strains commonly produced the cyclic Pro-Phe (cPF). Thirdly, the expression of non-ribosomal peptide synthetase (NRPS) genes varied greatly among the strains. NRPS genes were minimally expressed in the tolerant T. molitor and highly expressed in the susceptible M. vitrata. In M. vitrata, specific NRPS genes were markedly expressed in the virulent strains. Finally, cPF demonstrated potent immunosuppressive activity against the cellular and humoral responses of M. vitrata. The addition of cPF significantly enhanced the virulence against the tolerant T. molitor. These findings suggest that immunosuppression is necessary for the pathogenicity of Xenorhabdus bacteria, wherein NRPS products play a critical role in suppressing immune-associated factors in target insects. Full article

Currently, it is widely accepted that the type III secretion system (T3SS) serves as the transport platform for bacterial virulence factors, while flagella act as propulsion motors. However, there remains a noticeable dearth of comparative studies elucidating the functional disparities between these two mechanisms. Entomopathogenic nematode symbiotic bacteria (ENS), including Xenorhabdus and Photorhabdus, are Gram-negative bacteria transported into insect hosts by Steinernema or Heterorhabdus. Flagella are conserved in ENS, but the T3SS is only encoded in Photorhabdus. There are few reports on the function of flagella and the T3SS in ENS, and it is not known what role they play in the infection of ENS. Here, we clarified the function of the T3SS and flagella in ENS infection based on flagellar inactivation in X. stockiae (flhDC deletion), T3SS inactivation in P. luminescens (sctV deletion), and the heterologous synthesis of the T3SS of P. luminescens in X. stockiae. Consistent with the previous results, the swarming movement of the ENS and the formation of biofilms are dominated by the flagella. Both the T3SS and flagella facilitate ENS invasion and colonization within host cells, with minimal impact on secondary metabolite formation and secretion. Unexpectedly, a proteomic analysis reveals a negative feedback loop between the flagella/T3SS assembly and the type VI secretion system (T6SS). RT-PCR testing demonstrates the T3SS’s inhibition of flagellar assembly, while flagellin expression promotes T3SS assembly. Furthermore, T3SS expression stimulates ribosome-associated protein expression. Full article

Secondary metabolites, bioactive compounds produced by living organisms, can unveil symbiotic relationships in nature. In this study, soilborne entomopathogenic nematodes associated with symbiotic bacteria (Xenorhabdus stockiae and Photorhabdus luminescens) were extracted from solvent supernatant containing secondary metabolites, demonstrating significant inhibitory effects against E. coli, S. aureus, B. subtilus, P. mirabilis, E. faecalis, and P. stutzeri. The characterization of these secondary metabolites by Fourier transforms infrared spectroscopy revealed amine groups of proteins, hydroxyl and carboxyl groups of polyphenols, hydroxyl groups of polysaccharides, and carboxyl groups of organic acids. Furthermore, the obtained crude extracts were analyzed by high-performance liquid chromatography for the basic identification of potential bioactive peptides. Gas chromatography–mass spectrometry analysis of ethyl acetate extracts from Xenorhabdus stockiae identified major compounds including nonanoic acid derivatives, proline, paromycin, octodecanal derivatives, trioxa-5-aza-1-silabicyclo, 4-octadecenal, methyl ester, oleic acid, and 1,2-benzenedicarboxylicacid. Additional extraction from Photorhabdus luminescens yielded functional compounds such as indole-3-acetic acid, phthalic acid, 1-tetradecanol, nemorosonol, 1-eicosanol, and unsaturated fatty acids. These findings support the potential development of novel natural antimicrobial agents for future pathogen suppression. Full article

Sclerotinia sclerotiorum (Lib.) de Bary, a polyphagous necrotrophic fungal pathogen, has brought about significant losses in agriculture and floriculture. Until now, the most common method for controlling S. sclerotiorum has been the application of fungicides. Xenocoumacin 1 (Xcn1) is a potential biopesticide having versatile antimicrobial activities, generated by Xenorhabdus nematophila. This study was intended to isolate Xcn1 from X. nematophila YL001 and clarify its efficacies for S. sclerotiorum control. Xcn1 demonstrated a wider antifungal spectrum against 10 plant-pathogenic fungi. It also exhibited a strong inhibitory effect on the mycelial growth of S. sclerotiorum with an EC₅₀ value of 3.00 μg/mL. Pot experiments indicated that Xcn1 effectively inhibited disease extension on oilseed rape and broad bean plants caused by S. sclerotiorum. Morphological and ultrastructural observations revealed that the hyphae of S. sclerotiorum became twisted, shriveled, and deformed at the growing points after treatment with Xcn1 at 3.00 μg/mL and that the subcellular fractions also became abnormal concurrently, especially the mitochondrial structure. Moreover, Xcn1 also increased cell membrane permeability and decreased the content of exopolysaccharide as well as suppressing the activities of polygalacturonase and cellulase of S. sclerotiorum, but exerted no effects on oxalic acid production. This study demonstrated that Xcn1 has great potential to be developed as a new biopesticide for the control of S. sclerotiorum. Full article

Entomopathogenic nematodes from the genus Steinernema (Nematoda: Steinernematidae) are capable of causing the rapid killing of insect hosts, facilitated by their association with symbiotic Gram-negative bacteria in the genus Xenorhabdus (Enterobacterales: Morganellaceae), positioning them as interesting candidate tools for the control of insect pests. In spite of this, only a limited number of species from this bacterial genus have been identified from their nematode hosts and their insecticidal properties documented. This study aimed to perform the genome sequence analysis of fourteen Xenorhabdus strains that were isolated from Steinernema nematodes in Argentina. All of the strains were found to be able of killing 7th instar larvae of Galleria mellonella (L.) (Lepidoptera: Pyralidae). Their sequenced genomes harbour 110 putative insecticidal proteins including Tc, Txp, Mcf, Pra/Prb and App homologs, plus other virulence factors such as putative nematocidal proteins, chitinases and secondary metabolite gene clusters for the synthesis of different bioactive compounds. Maximum-likelihood phylogenetic analysis plus average nucleotide identity calculations strongly suggested that three strains should be considered novel species. The species name for strains PSL and Reich (same species according to % ANI) is proposed as Xenorhabdus littoralis sp. nov., whereas strain 12 is proposed as Xenorhabdus santafensis sp. nov. In this work, we present a dual insight into the biocidal potential and diversity of the Xenorhabdus genus, demonstrated by different numbers of putative insecticidal genes and biosynthetic gene clusters, along with a fresh exploration of the species within this genus. Full article

Fungal diseases such as Fusarium head blight (FHB) are significant biotic stressors, negatively affecting wheat production and quality. This study explored the antifungal activity of the metabolites produced by the bacterial symbionts of entomopathogenic nematodes (EPNs) against FHB-causing Fusarium sp. Fusarium graminearum. To achieve this, the symbiotic bacteria of nine EPN isolates from the EPN collection at the Agricultural Research Council-Small Grains (ARC-SG) were isolated from the cadavers of Galleria mellonella (Lepidoptera: Pyralidae) larvae after infection with EPNs. Broth cultures (crude) and their supernatants (filtered and autoclaved) of each bacterial isolate were used as bacterial metabolite treatments to test their inhibitory effect on the mycelial growth and spore germination of F. graminearum. Mycelial growth inhibition rates varied among both bacterial isolates and treatments. Crude metabolite treatments proved to be more effective than filtered and autoclaved metabolite treatments, with an overall inhibition rate of 75.25% compared to 23.93% and 13.32%, respectively. From the crude metabolite treatments, the Xenorhabdus khoisanae SGI 197 bacterial isolate from Steinernema beitlechemi SGI 197 had the highest mean inhibition rate of 96.25%, followed by Photorhabdus luminescens SGI 170 bacteria isolated from Heterorhabditis bacteriophora SGI 170 with a 95.79% mean inhibition rate. The filtered metabolite treatments of all bacterial isolates were tested for their inhibitory activity against Fusarium graminearum spore germination. Mean spore germination inhibition rates from Xenorhabdus spp. bacterial isolates were higher (83.91 to 96.29%) than those from Photorhabdus spp. (6.05 to 14.74%). The results obtained from this study suggest that EPN symbiotic bacterial metabolites have potential use as biological control agents of FHB. Although field efficacy against FHB was not studied, the significant inhibition of mycelial growth and spore germination suggest that the application of these metabolites at the flowering stage may provide protection to plants against infection with or spread of F. graminearum. These metabolites have the potential to be employed as part of integrated pest management (IPM) to inhibit/delay conidia germination until the anthesis (flowering stage) of wheat seedlings has passed. Full article