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Trends in Microbiology Apr 2001The toxin complex (tc) genes of Photorhabdus encode insecticidal, high molecular weight Tc toxins. These toxins have been suggested as useful alternatives to those... (Review)
Review
The toxin complex (tc) genes of Photorhabdus encode insecticidal, high molecular weight Tc toxins. These toxins have been suggested as useful alternatives to those derived from Bacillus thuringiensis for expression in insect-resistant transgenic plants. Although Photorhabdus luminescens is symbiotic with nematodes that kill insects, tc genes have recently been described from other insect-associated bacteria such as Serratia entomophila, an insect pathogen, and Yersinia pestis, the causative agent of bubonic plague, which has a flea vector. Here, recent advances in our understanding of the tc gene family are reviewed in view of their potential development as insect-control agents.
Topics: Animals; Bacterial Toxins; Cloning, Molecular; Genes, Bacterial; Insecticides; Nematoda; Pest Control, Biological; Photorhabdus; Symbiosis
PubMed: 11286884
DOI: 10.1016/s0966-842x(01)01978-3 -
Environmental Microbiology Reports Dec 2022Photorhabdus, the symbiotic bacteria of Heterorhabditis nematodes, has been reported to possess many non-ribosomal peptide synthetase (NRPS) biosynthesis gene clusters...
Photorhabdus, the symbiotic bacteria of Heterorhabditis nematodes, has been reported to possess many non-ribosomal peptide synthetase (NRPS) biosynthesis gene clusters (BGCs). To provide an in-depth assessment of the non-ribosomal peptide biosynthetic potential of Photorhabdus, we compared the distribution of BGCs in 81 Photorhabdus strains, confirming the predominant presence (44.80%) of NRPS BGCs in Photorhabdus. All 990 NRPS BGCs were clustered into 275 gene cluster families (GCFs) and only 13 GCFs could be annotated with known BGCs, suggesting their great diversity and novelty. These NRPS BGCs encoded 351 novel peptides containing more than four amino acids, and 173 of them showed high sequence similarity to known BGCs encoding bioactive peptides, implying the promising potential of Photorhabdus to produce valuable peptides. Sequence similarity networking of adenylation (A-) domains suggested that the substrate specificity of A-domains was not directly correlated with the sequence similarity. The molecular similarity network of predicted metabolite scaffolds of NRPS BGCs and reported peptides from Photorhabdus and a relevant database demonstrated that the non-ribosomal peptide biosynthetic potential of Photorhabdus was largely untapped and revealed the core peptides deserving intensive studies. Our present study provides valuable information for the targeted discovery of novel non-ribosomal peptides from Photorhabdus.
Topics: Animals; Photorhabdus; Nematoda; Multigene Family; Symbiosis; Peptides
PubMed: 35998886
DOI: 10.1111/1758-2229.13118 -
Nucleic Acids Research Aug 2021Bacteria have evolved sophisticated mechanisms to deliver potent toxins into bacterial competitors or into eukaryotic cells in order to destroy rivals and gain access to...
Bacteria have evolved sophisticated mechanisms to deliver potent toxins into bacterial competitors or into eukaryotic cells in order to destroy rivals and gain access to a specific niche or to hijack essential metabolic or signaling pathways in the host. Delivered effectors carry various activities such as nucleases, phospholipases, peptidoglycan hydrolases, enzymes that deplete the pools of NADH or ATP, compromise the cell division machinery, or the host cell cytoskeleton. Effectors categorized in the family of polymorphic toxins have a modular structure, in which the toxin domain is fused to additional elements acting as cargo to adapt the effector to a specific secretion machinery. Here we show that Photorhabdus laumondii, an entomopathogen species, delivers a polymorphic antibacterial toxin via a type VI secretion system. This toxin inhibits protein synthesis in a NAD+-dependent manner. Using a biotinylated derivative of NAD, we demonstrate that translation is inhibited through ADP-ribosylation of the ribosomal 23S RNA. Mapping of the modification further showed that the adduct locates on helix 44 of the thiostrepton loop located in the GTPase-associated center and decreases the GTPase activity of the EF-G elongation factor.
Topics: ADP-Ribosylation; Bacterial Toxins; GTP Phosphohydrolases; NAD; Peptide Elongation Factor G; Photorhabdus; Protein Biosynthesis; RNA, Ribosomal, 23S; Thiostrepton; Type VI Secretion Systems
PubMed: 34255843
DOI: 10.1093/nar/gkab608 -
Microbes and Infection Feb 2004The three currently recognised Photorhabdus species are bioluminescent bacteria that are pathogenic to insects. P. luminescens and P. temperata form a symbiotic... (Review)
Review
The three currently recognised Photorhabdus species are bioluminescent bacteria that are pathogenic to insects. P. luminescens and P. temperata form a symbiotic relationship with nematodes that infect insects. P. asymbiotica, on the other hand, has only been isolated from human clinical specimens from the USA and Australia. The bacterium has been associated with locally invasive soft tissue and disseminated bacteraemic infections. An invertebrate vector for P. asymbiotica has not yet been identified.
Topics: Communicable Diseases, Emerging; Humans; Luminescent Measurements; Photorhabdus; Rhabditida Infections
PubMed: 15049334
DOI: 10.1016/j.micinf.2003.10.018 -
Toxicon : Official Journal of the... Mar 2007Most of the insecticidal toxins used in agriculture come from a single bacterium Bacillus thuringiensis or 'Bt'. Here we review our work on the array of toxins produced... (Review)
Review
Most of the insecticidal toxins used in agriculture come from a single bacterium Bacillus thuringiensis or 'Bt'. Here we review our work on the array of toxins produced by Photorhabdus and Xenorhabdus bacteria that are symbiotic with entomopathogenic nematodes, and discuss their potential for use in agriculture as alternatives to Bt. Despite the fact that both Photorhabdus and Xenorhabdus are introduced directly into the insect blood stream by their nematode vectors, they produce a range of toxins with both oral and injectable insecticidal activity. The toxin complexes (Tc's) are large orally active toxins that are displayed on the outer surface of the bacterium. They require three components (A-C) for full toxicity and one 'A' component has been successfully expressed in transgenic Arabidopsis to confer insect resistance. One such group of Tc's, the PirAB binary toxins, have oral activity against mosquitoes and some caterpillar pests. Their mode of action is not known but they show significant sequence similarity to a recently described neurotoxin beta-leptinotarsin-h isolated from the blood of the Colorado potato beetle. Other toxins such as 'makes caterpillars floppy' (Mcf) and proteins encoded by the 'Photorhabdus virulence cassettes' (PVCs) only show injectable activity. Mcf1 promotes apoptosis in a wide range of cells and appears to mimic mammalian BH3 domain-only proteins in the mitochondrion whereas the mode of action of the PVCs remains undetermined. The likely biological reasons for the massive functional redundancy in Photorhabdus insecticidal toxins are discussed.
Topics: Agriculture; Animals; Bacterial Toxins; Insecticides; Pest Control, Biological; Photorhabdus; Plants, Genetically Modified
PubMed: 17207509
DOI: 10.1016/j.toxicon.2006.11.019 -
Applied and Environmental Microbiology Jun 2022Phytopathogens represent a large agricultural challenge. The use of chemical pesticides is harmful to the environment, animals, and humans. Therefore, new sustainable...
Phytopathogens represent a large agricultural challenge. The use of chemical pesticides is harmful to the environment, animals, and humans. Therefore, new sustainable and biological alternatives are urgently needed. The insect-pathogenic bacterium Photorhabdus luminescens, already used in combination with entomopathogenic nematodes (EPNs) as a biocontrol agent, is characterized by two different phenotypic cell forms, called primary (1°) and secondary (2°). The 1° cells are symbiotic with EPNs and are used for biocontrol, and the 2° cells are unable to undergo symbiosis with EPNs, remain in the soil after insect infection, and specifically interact with plant roots. A previous RNA sequencing (RNAseq) analysis showed that genes encoding the exochitinase Chi2A and chitin binding protein (CBP) are highly upregulated in 2° cells exposed to plant root exudates. Here, we investigate Chi2A and CBP functions and demonstrate that both are necessary for P. luminescens 2° cells to inhibit the growth of the phytopathogenic fungus Fusarium graminearum. We provide evidence that Chi2A digests chitin and thereby inhibits fungal growth. Furthermore, we show that 2° cells specifically colonize fungal hyphae as one of the first mechanisms to protect plants from fungal phytopathogens. Finally, soil pot bioassays proved plant protection from F. graminearum by 2° cells, where Chi2A and CPB were essential for this process. This work gives molecular insights into the new applicability of as a plant-growth-promoting and plant-protecting organism in agriculture. The enteric enterobacterium Photorhabdus luminescens is already being used as a bioinsecticide since it is highly pathogenic toward a broad range of insects. However, the bacteria exist in two phenotypically different cell types, called 1° and 2° cells. Whereas only 1° cells are symbiotic with their nematode partner to infect insects, 2° cells were shown to remain in the soil after an insect infection cycle. It was demonstrated that 2° cells specifically interact with plant roots. Here, we show that the bacteria are beneficial for the plants by protecting them from phytopathogenic fungi. Specific colonization of the fungus mycelium as well as chitin-degrading activity mediated by the chitin binding protein (CBP) and the chitinase Chi2A are essential for this process. Our data give evidence for the novel future applicability of as a plant-growth-promoting organism and biopesticide.
Topics: Animals; Chitin; Fusarium; Insecta; Nematoda; Photorhabdus; Soil; Symbiosis
PubMed: 35604230
DOI: 10.1128/aem.00645-22 -
Cell Apr 2019Contractile injection systems (CISs) are cell-puncturing nanodevices that share ancestry with contractile tail bacteriophages. Photorhabdus virulence cassette (PVC)...
Contractile injection systems (CISs) are cell-puncturing nanodevices that share ancestry with contractile tail bacteriophages. Photorhabdus virulence cassette (PVC) represents one group of extracellular CISs that are present in both bacteria and archaea. Here, we report the cryo-EM structure of an intact PVC from P. asymbiotica. This over 10-MDa device resembles a simplified T4 phage tail, containing a hexagonal baseplate complex with six fibers and a capped 117-nanometer sheath-tube trunk. One distinct feature of the PVC is the presence of three variants for both tube and sheath proteins, indicating a functional specialization of them during evolution. The terminal hexameric cap docks onto the topmost layer of the inner tube and locks the outer sheath in pre-contraction state with six stretching arms. Our results on the PVC provide a framework for understanding the general mechanism of widespread CISs and pave the way for using them as delivery tools in biological or therapeutic applications.
Topics: Bacteriophage T4; Cell Membrane; Cryoelectron Microscopy; Models, Molecular; Photorhabdus; Protein Conformation; Type VI Secretion Systems
PubMed: 30905475
DOI: 10.1016/j.cell.2019.02.020 -
Current Opinion in Microbiology Jun 2012Insects are the largest group of animals on earth. Like mammals, virus, fungi, bacteria and parasites infect them. Several tissue barriers and defense mechanisms are... (Review)
Review
Insects are the largest group of animals on earth. Like mammals, virus, fungi, bacteria and parasites infect them. Several tissue barriers and defense mechanisms are common for vertebrates and invertebrates. Therefore some insects, notably the fly Drosophila and the caterpillar Galleria mellonella, have been used as models to study host-pathogen interactions for several insect and mammal pathogens. They are excellent tools to identify pathogen determinants and host tissue cell responses. We focus here on the comparison of effectors used by two different groups of bacterial insect pathogens to accomplish the infection process in their lepidopteran larval host: Bacillus thuringiensis and the nematode-associated bacteria, Photorhabdus and Xenorhabdus. The comparison reveals similarities in function and expression profiles for some genes, which suggest that such factors are conserved during evolution in order to attack the tissue encountered during the infection process.
Topics: Animal Diseases; Animals; Bacillus thuringiensis; Host-Pathogen Interactions; Insecta; Photorhabdus; Xenorhabdus
PubMed: 22633889
DOI: 10.1016/j.mib.2012.04.006 -
Naunyn-Schmiedeberg's Archives of... Mar 2011Photorhabdus luminescens produces several types of protein toxins, which are essential for participation in a trilateral symbiosis with nematodes and insects. The... (Review)
Review
Photorhabdus luminescens produces several types of protein toxins, which are essential for participation in a trilateral symbiosis with nematodes and insects. The nematodes, carrying the bacteria, invade insect larvae and release the bacteria, which kill the insects with their toxins. Recently, the molecular mechanisms of the toxin complexes PTC3 and PTC5 have been elucidated. The biologically active components of the toxin complexes are ADP-ribosyltransferases, which modify actin and Rho GTPases, respectively. The actions of the toxins are described and compared with other bacterial protein toxins acting on the cytoskeleton.
Topics: ADP Ribose Transferases; Actins; Animals; Bacterial Toxins; Cytoskeleton; Humans; Insecticides; Photorhabdus; rho GTP-Binding Proteins
PubMed: 21072628
DOI: 10.1007/s00210-010-0579-5 -
Current Topics in Microbiology and... 2017Photorhabdus asymbiotica is a species of bacterium that is pathogenic to humans whilst retaining the ability to infect insect hosts. Currently, there are two recognised...
Photorhabdus asymbiotica is a species of bacterium that is pathogenic to humans whilst retaining the ability to infect insect hosts. Currently, there are two recognised subspecies, P. asymbiotica subsp. asymbiotica and P. asymbiotica subsp. australis with strains isolated from various locations in the USA, Australia, Thailand, Nepal and Europe. Like other species of Photorhabdus, P. asymbiotica subsp. australis was shown to form a symbiotic relationship with a Heterorhabditis nematode. In contrast to most strains of Photorhabdus luminescens, P. asymbiotica can grow at 37 °C and this is a defining factor in its ability to cause human disease. Insights into other adaptations it has undergone that have enabled host switching to occur have come from whole genome sequencing and transcriptomic studies. P. asymbiotica has a smaller genome compared to P. luminenscens with a lower diversity of insecticidal toxins. However, it has acquired plasmids and several pathogenicity islands in its genome. These encode genes with similarity to effectors or systems found in other known human pathogens such as Salmonella and Yersinia and are therefore likely to contribute to human pathogenicity. Of crucial importance to virulence is the fact that P. asymbiotica undergoes a large metabolic shift at the human host temperature.
Topics: Animals; Australia; Europe; Genome; Humans; Insecta; Photorhabdus; Virulence
PubMed: 27726002
DOI: 10.1007/82_2016_29