Evolution and taxonomy of nematode-associated entomopathogenic bacteria of the genera Xenorhabdus and Photorhabdus: an overview (original) (raw)
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Entomopathogenic symbiotic bacteria, Xenorhabdus and Photorhabdus of nematodes
World Journal of Microbiology & Biotechnology, 2001
Xenorhabdus and Photorhabdus species are entomopathogenic bacteria with a wide insect host range, that belong to the family Enterobacteriaceae. Xenorhabdus and Photorhabdus species symbiotically associate with nematodes of the families Steinernematidae and Heterorhabditidae respectively. The factor(s) determining the symbiotic interaction between nematodes and bacteria are yet to be identified. Xenorhabdus and Photorhabdus species exist in two main phenotypic forms, a phenomenon known as phase variation. The phase I (or primary form) varies from phase II (or secondary form) in certain physiological and morphological characteristics. There is no variation in the DNA integrity of phase I and phase II and this supports epigenetic regulatory mechanism in phase variation. Certain pathogenic determinants such as pili, lipopolysaccharides and toxins contribute to the pathogenicity of Xenorhabdus and Photorhabdus species, and both appear to be equally pathogenic to insects. The observed similarity in their virulence to insect hosts may reflect possible in vivo conversion of phase II to phase I, however the host cellular invasion and virulence is yet to be properly understood. The virulence of Xenorhabdus variants varies among insects apparently due to factors which include the feeding habits of the insects. The molecular mechanism and biological significance of phase variation are presently unknown.
Journal of Crop Protection, 2017
By conducting three different methods, we report on the isolation of five novel strains of non-symbiotic bacteria from crushed infective juveniles (IJs) of four species of entomopathogenic nematodes (EPN) including Heterorhabditis bacteriophora, Steinernema carpocapsae, Steinernema feltiae, and Steinernema glaseri and five bacterial species from hemolymph of insect larvae infected with EPNs. Samples of hemolymph of infected Galleria mellonella L. larvae by EPNs and crushed surface sterilized IJs were bulk streaked onto both MacConkey and NBTA agar. To further ensure diagnoses, extracted DNA from IJs bulk was subjected to PCR by 16S-rRNA bacterial universal primers. Bacteria were identified using biochemical and phylogenetic analysis. Based on 16S-rRNA gene sequence, maximum parsimony, maximum likelihood and neighbour joining phylogenetic analyses were conducted, as well as comparisons of predicted RNA secondary structures. Four species of bacteria were identified including: Stenotro...
Current Microbiology, 2012
Photorhabdus are motile Gram-negative bacteria that have a mutualistic association with Heterorhabditis nematodes (Heterorhabditidae). These bacteria possess peculiar biochemical characteristics such as inability to reduce nitrates, and the capacity to ferment only a limited number of carbohydrates. Heterorhabditis nematodes vector the bacteria from one insect host to another and also provide shelter to the bacteria from soil stressors and antagonists. Once inside the insect host, the bacterial symbionts are released and produce toxins and secondary metabolites and broad-spectrum antibiotics, which kill the host by septicemia within 48 h. At present, three Photorhabdus spp. have been identified: P. luminescens, P. temperata, and P. asymbiotica, and many subspecies have also been described. Characterization of new species and subspecies has been based on sequence data, mostly of the 16S rDNA, and also of a selection of protein coding genes. In addition to this, phenotypic traits including temperature growth, colony morphology, color, light production, carbohydrate response, and assimilation, among others, have been considered. In this study, we characterize the bacterial symbiont of Heterorbabditis sonorensis, a recently discovered entomopathogenic nematode species form the Sonoran desert in Arizona, USA. A selection of classic biochemical and molecular methods including sequence data of six genes: 16s rDNA, and four protein coding genes: gyrB, recA, gltX, and dnaN were considered. Evolutionary relationships of this new Photorhabdus subsp. were inferred considering maximum parsimony and Bayesian analyses.
Journal of Invertebrate Pathology, 2015
Xenorhabdus bacteria (γ-proteobacteria: Enterobacteriaceae) have dual lifestyles. They have a mutualistic relationship with Steinernema nematodes (Nematoda: Steinernematidae) and are pathogenic to a wide range of insects. Each Steinernema nematode associates with a specific Xenorhabdus species. However, a Xenorhabdus species can have multiple nematode hosts. For example, Xenorhabdus bovienii (Xb) colonizes at least nine Steinernema species from two different phylogenetic clades. The Steinernema-Xb partnership has been found in association with different insect hosts. Biological and molecular data on the Steinernema jollieti-Xb strain SS-2004 pair have recently been described. In particular, the Xb SS-2004 bacteria are virulent alone after direct injection into insect, making this strain a model for studying Xb virulence. In this study, we searched for Xb strains attenuated in virulence. For this purpose, we underwent infection assays with five Steinernema spp.-Xb pairs with two insects, Galleria mellonella (Lepidoptera: Pyralidae) and Spodoptera littoralis (Lepidoptera: Noctuidae). The S. weiseri-Xb CS03 pair showed attenuated virulence and lower fitness in S. littoralis in comparison to the other nematode-bacteria pairs. Furthermore, when injected alone into the hemolymph of G. mellonella or S. littoralis, the Xb CS03 bacterial strain was the only non-virulent strain. By comparison with the virulent Xb SS-2004 strain, Xb CS03 showed an increased sensitivity to the insect antimicrobial peptides, suggesting an attenuated response to the insect humoral immunity. To our current knowledge, Xb CS03 is the first non-virulent Xb strain identified. We propose this strain as a new model for studying the Xenorhabdus virulence.
International Journal of Systematic Bacteriology, 1993
The levels of DNA relatedness for a broad sample ofXenorhabdus strains isolated from different species of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) and from different geographical sources were estimated by the hydroxyapatite method. The level of DNA-DNA relatedness for the two phases of each isolate tested was not significantly different from lo%, demonstrating unequivocally that the phase variation demonstrated by all Xenorhabdus spp. is not due to contamination. The isolates of the described Xenorhabdus species coalesced into different DNA relatedness groups, confirming that Xenorhubdus nemutophilus, Xenorhabdus bovienii, Xenorhubdus poinarii, and Xenorhabdus beddingii, defined on the basis of phenotypic differences, are valid species. The symbiont of Steinernemu intermedia also coalesced with the X. bovienii isolates. This was the only symbiont of seven recently described and unamed Steinernema spp. (including Steinernemu ritteri, Steinemem rara, and Steinernemu anomali) that formed a group with any of the previously described Xenorhabdus species; new species descriptions are required to accommodate the other taxa, but too few isolates were available to allow satisfactory descriptions of them. The DNA relatedness data also showed that the bacteria currently classified as Xenorhabdus luminescens are significantly different from all other Xenorhubdus strains. These data strongly support indications from previous studies of phenotypic characteristics, cellular fatty acids, and DNA relatedness that X. luminescens should be classified as a separate genus, A new genus, Photorhabdus, with an amended description of the type species, Photorhabdus luminescens, is proposed.
Journal of helminthology, 2014
The entomopathogenic nematode Steinernema yirgalemense is considered a promising agent in the biocontrol of insects. However, little is known about the bacteria living in symbiosis with the nematode. In this study, we have identified the only available bacterial strain (157-C) isolated from S. yirgalemense, as a member of the species Xenorhabdus indica. Identification was based on 16S rDNA, recA, dnaN, gltX, gyrB and infB gene sequence analyses. The relatedness of strain 157-C to the type strain of X. indica (DSM 17 382) was confirmed with DNA-DNA hybridization. The phenotypic characteristics of strain 157-C are similar to those described for the type strain of X. indica. This is the first report associating X. indica with S. yirgalemense.
TURKISH JOURNAL OF ZOOLOGY, 2015
The entomopathogenic nematode species (EPNs) of 2 genera, Heterorhabditis and Steinernema, are effective biological control agents against major insect pests (Kaya and Gaugler, 1993). These nematodes each contain symbiotic bacteria, with Photorhabdus spp. for Heterorhabditis and Xenorhabdus spp. for Steinernema (Akhurst, 1980; Boemare et al., 1993). The symbiotic bacteria reside in the nematode intestine (for Heterorhabditis) or in a bacterial vesicle (for Steinernema) and are released into the insect hemocoel when the nematode enters the target insect host (Dowds and Peters, 2002). The bacteria multiply, producing septicemia, and kill the insect host within 24 to 48 h, allowing the colonizing nematodes to feed on both the bacteria and the digested insect tissues (Dunphy and Webster, 1988; Park and Kim, 2000). Once developed, infective juveniles (IJs) emerge from the cadaver and search for another host. These bacteria are of interest not only for the mutualistic association with EPNs, but also for their production of toxins, antibiotics, and enzymes (Webster et al., 2002; Park and Forst, 2006; Proschak et al., 2011). As there are currently no selective media for these bacteria and freeliving forms of these bacteria have not yet been discovered, to carry out research on these bacteria, they must first be isolated from their nematode hosts. Three methods have been used for isolating symbiotic bacteria from entomopathogenic nematodes. The "hanging drop" method uses a sterile drop of insect hemolymph,
Biopesticide International, 2017
Entomopathogenic nematodes (EPNs) belonging to the families heterorhabditidae (genus Heterorhabditis) and steinernematidae (genus Steinernema) are mutualistically associated with bacteria in the family Enterobacteriaceae (Photorhabdus spp. for Heterorhabditis and Xenorhabdus spp. for Steinernema). At present, there are 100 Steinernema and 17 Heterorhabditis species and 20 Xenorhabdus and 4 Photorhabdus species. In general, each EPN species has its own bacterial species, but a given bacterial species may be associated with more than one EPN species. The EPNs' natural habitat is the soil where the nematode-bacterium complex infects many different insect species killing them within 48 h. EPNs have been isolated from many different islands and from all continents except antarctica. Because EPNs and their associated bacteria are safe to humans, other vertebrates, and plants, can effectively kill soil insect pests in a short time, serve as an alternative to chemical pesticides, are easily massed produced in vivo and in vitro, and do not require registration in many countries, a number of EPN species have been produced commercially to target soil and plant-boring pests in high value crops. Moreover, the associated bacteria produce antibiotics and other compounds that have potential to be used against human, veterinary, and plant pathogens.