Photorhabdus aballayi sp. nov. and Photorhabdus luminescens subsp. venezuelensis subsp. nov., isolated from Heterorhabditis amazonensis entomopathogenic nematodes

Six Gram-negative, rod-shaped bacterial strains isolated from Heterorhabditis amazonensis entomopathogenic nematodes were characterized to determine their taxonomic position. 16S rRNA and gyrB gene sequences indicate that they belong to the class Gammaproteobacteria, family Morganellaceae and genus Photorhabdus, and that some of them are conspecifics. Two of them, APURE^T and JAR^T, were selected for further molecular characterization using whole genome- and whole-proteome-based phylogenetic reconstructions and sequence comparisons. Phylogenetic reconstructions using whole genome and whole proteome sequences show that strains APURE^T and JAR^T are closely related to Photorhabdus luminescens subsp. luminescens ATCC 29999^T and to P. luminescens subsp. mexicana MEX47-22^T. Moreover, digital DNA-DNA hybridization (dDDH) values between APURE^T and P. luminescens subsp. luminescens ATCC 29999^T, APURE^T and P. luminescens subsp. mexicana MEX47-22^T, and APURE^T and JAR^T are 61.6, 61.2 and 64.1 %, respectively. These values are below the 70 % divergence threshold that delimits prokaryotic species. dDDH scores between JAR^T and P. luminescens subsp. luminescens ATCC 29999^T and between JAR^T and P. luminescens subsp. mexicana MEX47-22^T are 71.9 and 74.8 %, respectively. These values are within the 70 and 79 % divergence thresholds that delimit prokaryotic subspecies. Based on these genomic divergence values, APURE^T and JAR^T represent two different taxa, for which we propose the names: Photorhabdus aballayi sp. nov. with APURE^T (=CCM 9236^T =CCOS 2019^T) as type strain and Photorhabdus luminescens subsp. venezuelensis subsp. nov. with JAR^T (=CCM 9235^T =CCOS 2021^T) as type strain. Our study contributes to a better understanding of the biodiversity of an important bacterial group with enormous biotechnological and agricultural potential.

Photorhabdus antumapuensis sp. nov., a novel symbiotic bacterial species associated with Heterorhabditis atacamensis entomopathogenic nematodes

One motile, Gram-negative, non-spore-forming and rod-shaped symbiotic bacterium, strain UCH-936T, was isolated from Heterorhabditis atacamensis nematodes. Results of biochemical, physiological, molecular and genomic analyses suggest that it represents a new species, which we propose to name Photorhabdus antumapuensis sp. nov. Digital DNA–DNA hybridization shows that strain UCH-936T is more closely related to Photorhabdus kleinii DSM 23513T, but shares solely 50.5 % similarity, which is below the 70% cut-off value that delimits species boundaries in bacteria. Phylogenetic reconstructions using whole-genome sequences show that strain UCH-936T forms a unique clade, suggesting its novel and distinct taxonomic status again. Similarly, comparative genomic analyses shows that the virulence factor flagella-related gene fleR, the type IV pili-related gene pilL and the vibriobactin-related gene vibE are present in the genome of strain UCH-936T but absent in the genomes of its closest relatives. Biochemically and physiologically, UCH-936T differs also from all closely related Photorhabdus species. Therefore, Photorhabdus antumapuensis sp. nov. is proposed as a new species with the type strain UCH-936T (CCCT 21.06T=CCM 9188T=CCOS 1991T).

In vitro liquid culture of the mollusc-parasitic nematode Phasmarhabditis (Rhabditida: Rhabditidae)

The success of the mollusc-parasitic nematode, Phasmarhabditis hermaphrodita (Schneider) Andrássy (Rhabditida: Rhabditidae), as a biological control agent in Europe has led to worldwide interest in phasmarhabditids as biocontrol agents. In this study, the mass culture potential of three phasmarhabditids, namely Phasmarhabditis papillosa, Phasmarhabditis kenyaensis and Phasmarhabditis bohemica, was assessed. In addition, ten bacterial candidates, consisting of seven associated with slugs and three associated with entomopathogenic nematodes, were investigated. The bacteria were tested for their ability to cause mortality to Deroceras invadens, as well as to support nematode growth. Initial mortality studies demonstrated that Kluyvera, Aeromonas and Pseudomonas spp. (AP3) caused 100% mortality when they were injected into the haemocoel of D. invadens. However, in growth studies, Pseudomonas sp. (AP4) was found to be the most successful bacterium, leading to recovery and reproduction in almost all nematode species, except for P. kenyaensis. In flask studies, P. bohemica, which showed exceptional growth with Pseudomonas sp. (AP1), was chosen for further investigation. The effect of inoculating flasks with different concentrations of Pseudomonas sp. (AP1), as well as with different concentrations of P. bohemica, was evaluated by assessing the nematode populations for 14 days. The results indicated that the lowest, 1% (v/v), bacteria inoculation led to higher total nematode and to infective juvenile (IJ) yield, with flasks with the highest IJ inoculum (3000 IJs/ml) having a positive effect on the total number of nematodes and IJs in cultures of P. bohemica. This study presents improvements for the mass-culturing of nematodes associated with molluscs.

Photorhabdus hindustanensis sp. nov., Photorhabdus akhurstii subsp. akhurstii subsp. nov., and Photorhabdus akhurstii subsp. bharatensis subsp. nov., isolated from Heterorhabditis entomopathogenic nematodes

Two Gram-negative, rod-shaped bacteria, H1^T and H3^T, isolated from the digestive tract of Heterorhabditis entomopathogenic nematodes were biochemically and molecularly characterized to determine their taxonomic positions. The 16S rRNA gene sequences of these strains indicate that they belong to the Gammaproteobacteria, to the family Morganellaceae, and to the Photorhabdus genus. Deeper analyses using whole genome-based phylogenetic reconstructions show that strains H1^T and H3^T are closely related to P. akhurstii DSM 15138^T, to P. hainanensis DSM 22397^T, and to P. namnaonensis PB45.5^T. In silico genomic comparisons confirm these observations and show that strain H1^T shares 70.6, 66.8, and 63.5 % digital DNA-DNA hybridization (dDDH) with P. akhurstii DSM 15138^T, P. hainanensis DSM 22397^T, and P. namnaonensis PB45.5^T, respectively, and that strain H3^T shares 76.6, 69.4, and 59.2 % dDDH with P. akhurstii DSM 15138^T, P. hainanensis DSM 22397^T, and P. namnaonensis PB45.5^T, respectively. Physiological and biochemical characterization reveals that these two strains differ from most of the validly described Photorhabdus species and from their more closely related taxa. Given the clear phylogenetic separations, that the threshold to discriminate species and subspecies is 70 and 79% dDDH, respectively, and that strains H1^T and H3^T differ physiologically and biochemically from their more closely related taxa, we propose to classify H1^T and H3^T into new taxa as follows: H3^T as a new subspecies within the species P. akhurstii, and H1^T as a new species within the Photorhabdus genus, in spite that H1^T shares 70.6 % dDDH with P. akhurstii DSM 15138^T, score that is slightly higher than the 70 % threshold that delimits species boundaries. The reason for this is that H1^T and P. akhurstii DSM 15138^T cluster apart in the phylogenetic trees and that dDDH scores between strain H1^T and other P. akhurstii strains are lower than 70 %. Hence, the following names are proposed: Photorhabdus hindustanensis sp. nov. with the type strain H1^T (=IARI-SGMG3^T,=KCTC 82683^T=CCM 9150^T=CCOS 1975^T) and P. akhurstii subsp. bharatensis subsp. nov. with the type strain H3^T (=IARI-SGHR2^T=KCTC 82684^T=CCM 9149^T=CCOS 1976^T). These propositions automatically create P. akhurstii subsp. akhurstii subsp. nov. with DSM 15138^T as the type strain (currently classified as P. akhurstii).

Photorhabdus spp.: An Overview of the Beneficial Aspects of Mutualistic Bacteria of Insecticidal Nematodes

The current approaches to sustainable agricultural development aspire to use safer means to control pests and pathogens. Photorhabdus bacteria that are insecticidal symbionts of entomopathogenic nematodes in the genus Heterorhabditis can provide such a service with a treasure trove of insecticidal compounds and an ability to cope with the insect immune system. This review highlights the need of Photorhabdus-derived insecticidal, fungicidal, pharmaceutical, parasiticidal, antimicrobial, and toxic materials to fit into current, or emerging, holistic strategies, mainly for managing plant pests and pathogens. The widespread use of these bacteria, however, has been slow, due to cost, natural presence within the uneven distribution of their nematode partners, and problems with trait stability during in vitro culture. Yet, progress has been made, showing an ability to overcome these obstacles via offering affordable mass production and mastered genome sequencing, while detecting more of their beneficial bacterial species/strains. Their high pathogenicity to a wide range of arthropods, efficiency against diseases, and versatility, suggest future promising industrial products. The many useful properties of these bacteria can facilitate their integration with other pest/disease management tactics for crop protection.

Identification of Photorhabdus symbionts by MALDI-TOF MS

Species of the bacterial genus Photorhabus live in a symbiotic relationship with Heterorhabditis entomopathogenic nematodes. Besides their use as biological control agents against agricultural pests, some Photorhabdus species are also a source of natural products and are of medical interest due to their ability to cause tissue infections and subcutaneous lesions in humans. Given the diversity of Photorhabdus species, rapid and reliable methods to resolve this genus to the species level are needed. In this study, we evaluated the potential of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the identification of Photorhabdus species. To this end, we established a collection of 54 isolates consisting of type strains and multiple field strains that belong to each of the validly described species and subspecies of this genus. Reference spectra for the strains were generated and used to complement a currently available database. The extended reference database was then used for identification based on the direct transfer sample preparation method and the protein fingerprint of single colonies. High-level discrimination of distantly related species was observed. However, lower discrimination was observed with some of the most closely related species and subspecies. Our results therefore suggest that MALDI-TOF MS can be used to correctly identify Photorhabdus strains at the genus and species level, but has limited resolution power for closely related species and subspecies. Our study demonstrates the suitability and limitations of MALDI-TOF-based identification methods for assessment of the taxonomic position and identification of Photorhabdus isolates.

Photorhabdus heterorhabditis subsp. aluminescens subsp. nov., Photorhabdus heterorhabditis subsp. heterorhabditis subsp. nov., Photorhabdus australis subsp. thailandensis subsp. nov., Photorhabdus australis subsp. australis subsp. nov., and Photorhabdus aegyptia sp. nov. isolated from Heterorhabditis entomopathogenic nematodes

Three Gram-stain-negative, rod-shaped, non-spore-forming bacteria, BA1^T, Q614^T and PB68.1^T, isolated from the digestive system of Heterorhabditis entomopathogenic nematodes, were biochemically and molecularly characterized to clarify their taxonomic affiliations. The 16S rRNA gene sequences of these strains suggest that they belong to the Gammaproteobacteria, to the family Morganellacea, and to the genus Photorhabdus. Deeper analyses using whole genome-based phylogenetic reconstructions suggest that BA1^T is closely related to Photorhabdus akhursti, that Q614^T is closely related to Photorhabdus heterorhabditis, and that PB68.1^T is closely related to Photorhabdus australis. In silico genomic comparisons confirm these observations: BA1^T and P. akhursti 15138^T share 68.8 % digital DNA-DNA hybridization (dDDH), Q614^T and P. heterorhabditis SF41^T share 75.4 % dDDH, and PB68.1^T and P. australis DSM 17609^T share 76.6  % dDDH. Physiological and biochemical characterizations reveal that these three strains also differ from all validly described Photorhabdus species and from their more closely related taxa, contrary to what was previously suggested. We therefore propose to classify BA1^T as a new species within the genus Photorhabdus, Q614^T as a new subspecies within P. heterorhabditis, and PB68.1^T as a new subspecies within P. australis. Hence, the following names are proposed for these strains: Photorhabdus aegyptia sp. nov. with the type strain BA1^T(=DSM 111180^T=CCOS 1943^T=LMG 31957^T), Photorhabdus heterorhabditis subsp. aluminescens subsp. nov. with the type strain Q614^T (=DSM 111144^T=CCOS 1944^T=LMG 31959^T) and Photorhabdus australis subsp. thailandensis subsp. nov. with the type strain PB68.1^T (=DSM 111145^T=CCOS 1942^T). These propositions automatically create Photorhabdus heterorhabditis subsp. heterorhabditis subsp. nov. with SF41^T as the type strain (currently classified as P. heterorhabditis) and Photorhabdus australis subsp. australis subsp. nov. with DSM17609^T as the type strain (currently classified as P. australis).

Evolution and taxonomy of nematode-associated entomopathogenic bacteria of the genera Xenorhabdus and Photorhabdus: an overview

Entomopathogenic bacteria from the genera Photorhabdus and Xenorhabdus are closely related Gram-negative bacilli from the family Enterobacteriaceae (γ-Proteobacteria). They establish obligate mutualistic associations with soil nematodes from the genera Steinernema and Heterorhabditis to facilitate insect pathogenesis. The research of these two bacterial genera is focused mainly on their unique interactions with two different animal hosts, i.e. nematodes and insects. So far, studies of the mutualistic bacteria of nematodes collected from around the world have contributed to an increase in the number of the described Xenorhabdus and Photorhabdus species. Recently, the classification system of entomopatogenic nematode microsymbionts has undergone profound revision and now 26 species of the genus Xenorhabdus and 19 species of the genus Photorhabdus have been identified. Despite their similar life style and close phylogenetic origin, Photorhabdus and Xenorhabdus bacterial species differ significantly in e.g. the nematode host range, symbiotic strategies for parasite success, and arrays of released antibiotics and insecticidal toxins. As the knowledge of the diversity of entomopathogenic nematode microsymbionts helps to enable the use thereof, assessment of the phylogenetic relationships of these astounding bacterial genera is now a major challenge for researchers. The present article summarizes the main information on the taxonomy and evolutionary history of Xenorhabdus and Photorhabdus, entomopathogenic nematode symbionts.

Photorhabdus khanii subsp. guanajuatensis subsp. nov., isolated from Heterorhabditis atacamensis, and Photorhabdus luminescens subsp. mexicana subsp. nov., isolated from Heterorhabditis mexicana entomopathogenic nematodes

Two Gram-negative, rod-shaped, non-spore-forming bacteria, MEX20-17^T and MEX47-22^T, were isolated from the digestive system of Heterorhabditis atacamensis and Heterorhabditis mexicana entomopathogenic nematodes, respectively. Their 16S rRNA gene sequences suggest that strains MEX20-17^T and MEX47-22^T belong to the γ-Proteobacteria and to the genus Photorhabdus. Deeper analyses using housekeeping-gene-based and whole-genome-based phylogenetic reconstruction suggest that MEX20-17^T is closely related to Photorhabdus khanii and that MEX47-22^T is closely related to Photorhabdus luminescens. Sequence similarity scores confirm these observations: MEX20-17^T and P. khanii DSM 3369^T share 98.9 % nucleotide sequence identity (NSI) of concatenated housekeeping genes, 70.4 % in silico DNA-DNA hybridization (isDDH) and 97 % orthologous average nucleotide identity (orthoANI); and MEX47-22^T and P. luminescens ATCC 29999^T share 98.9 % NSI, 70.6 % isDDH and 97 % orthoANI. Physiological characterization indicates that both strains differ from all validly described Photorhabdus species and from their more closely related taxa. We therefore propose to classify MEX20-17^T and MEXT47-22^T as new subspecies within P. khanii and P. luminescens, respectively. Hence, the following names are proposed for these strains: Photorhabdus khanii subsp. guanajuatensis subsp. nov. with the type strain MEX20-17^T (=LMG 30372^T=CCOS 1191^T) and Photorhabdus luminescenssubsp. mexicana subsp. nov. with the type strain MEX47-22^T (=LMG 30528^T=CCOS 1199^T). These propositions automatically create Photorhabdus khanii subsp. khanii subsp. nov. with DSM 3369^T as the type strain (currently classified as P. khanii), and Photorhabdus luminescenssubsp. luminescenssubsp. nov. with ATCC 29999^T as the type strain (currently classified as P. luminescens).

Diversity of entomopathogenic nematodes and their symbiotic bacteria in south African plantations and indigenous forests

The occurrence and diversity of entomopathogenic nematodes (EPN) and their symbiotic bacteria was evaluated in commercial forestry plantations (Eucalyptus spp., Pinus spp. and Acacia mearnsii) and indigenous forests in South Africa. EPN were most prevalent in A. mearnsii plantations, accounting for 60.7% of the isolates, while indigenous forests, plantations of Pinus spp. and Eucalyptus spp. accounted for 35.7, 3.6 and 0% of the isolates, respectively. DNA sequences of the internal transcribed spacer (ITS) and D2-D3 28S rDNA regions were used to identify the nematode species. Four Steinernema spp. were identified, including S. citrae, S. sacchari, two undescribed species, as well as Heterorhabditis bacteriophora and H. baujardi. Heterorhabditis baujardi is reported from South Africa for the first time. Analysis of 16S rRNA of the bacteria confirmed the presence of at least three Xenorhabdus species from Steinernema isolates and two subspecies of Photorhabdus luminescens from Heterorhabditis species.

First report of a symbiotic relationship between Xenorhabdus griffiniae and an unknown Steinernema from South Africa

Strain WS9, a mutualistic-associated bacterium, was isolated from an unknown entomopathogenic Steinernema nematode, collected from a litchi orchard in Friedenheim, Mpumalanga, South Africa. Based on phenotypic and phylogenetic data of the 16S rRNA, gltX, recA, dnaN, gyrB and infB gene sequences, strain WS9 is identified as X. griffiniae. Strain WS9 has antibacterial activity against Gram-positive and Gram-negative bacteria. This is the first report of an association between X. griffiniae and an unknown Steinernema species from South Africa.

Screening of the Antimicrobial Activity against Drug Resistant Bacteria of Photorhabdus and Xenorhabdus Associated with Entomopathogenic Nematodes from Mae Wong National Park, Thailand

Photorhabdus and Xenorhabdus are symbiotic with entomopathogenic nematodes (EPNs) of the genera Heterorhabditis and Steinernema, respectively. These bacteria produce several secondary metabolites including antimicrobial compounds. The objectives of this study were to isolate and identify EPNs and their symbiotic bacteria from Mae Wong National Park, Thailand and to evaluate the antibacterial activities of symbiont extracts against drug resistant bacteria. A total of 550 soil samples from 110 sites were collected between August 2014 and July 2015. A total of EPN isolates were obtained through baiting and White trap methods, which yielded 21 Heterorhabditis and 3 Steinernema isolates. Based on molecular identification and phylogenetic analysis, the most common species found in the present study was P. luminescens subsp. akhurstii associated with H. indica. Notably, two species of EPNs, H. zealandica and S. kushidai, and two species of symbiotic bacteria, X. japonica and P. temperata subsp. temperata represented new recorded organisms in Thailand. Furthermore, the association between P. temperata subsp. temperata and H. zealandica has not previously been reported worldwide. Disk diffusion, minimal inhibitory concentration, and minimal bactericidal concentration analyses demonstrated that the crude compound extracted by ethyl acetate from P. temperata subsp. temperata could inhibit the growth of up to 10 strains of drug resistant bacteria. Based on HPLC-MS analysis, compound classes in bacterial extracts were identified as GameXPeptide, xenoamicin, xenocoumacin, mevalagmapeptide phurealipids derivatives, and isopropylstilbene. Together, the results of this study provide evidence for the diversity of EPNs and their symbiotic bacteria in Mae Wong National Park, Thailand and demonstrate their novel associations. These findings also provide an important foundation for further research regarding the antimicrobial activity of Photorhabdus bacteria.

Three Novel Xenorhabdus-Steinernema Associations and Evidence of Strains of X. khoisanae Switching Between Different Clades

Xenorhabdus species are normally closely associated with entomopathogenic nematodes of the family Steinernematidae. Strain F2, isolated from Steinernema nguyeni, was identified as Xenorhabdus bovienii and strains J194 and SB10, isolated from Steinernema jeffreyense and Steinernema sacchari as Xenorhabdus khoisanae, based on phenotypic characteristics and sequencing of 16S rRNA and housekeeping genes dnaN, gltX, gyrB, infB and recA. All three strains produced antimicrobial compounds that inhibited the growth of Gram-positive and Gram-negative bacteria. This is the first report of associations between strains of the symbiotic bacteria X. bovienii with S. nguyeni, and X. khoisanae with S. jeffreyense and S. sacchari. This provides evidence that strains of Xenorhabdus spp. may switch between nematode species within the same clade and between different clades.

Photorhabdusluminescens subsp. namnaonensis subsp. nov., isolated from Heterorhabditisbaujardi nematodes

A lightly yellowish-pigmented, oxidase-negative bacterial strain (PB45.5T) isolated from the Nam Nao district of Phetchabun in central Thailand was investigated to determine its taxonomic position. Cells of the isolate showed a rod shaped appearance. The strain stained Gram-negative. Strain PB45.5T shared highest 16S rRNA gene sequence similarity with the type strains of Photorhabdus luminescens subsp. akhurstii (99.2 %) and Photorhabdus luminescens subsp. hainanensis (99.1 %) and lower similarities to all other Photorhabdus luminescens subspecies (<98.0 %). Multilocus sequence analysis (MLSA) based on concatenated partial recA, dnaN, gltX, gyrB and infB gene sequences confirmed the affiliation obtained by 16S rRNA gene sequence analysis but showed a clear distinction of PB45.5T from the closest related type strains. Strain PB45.5T shared only 96.9 % sequence similarity (concatenated nucleotide sequences) with P. luminescens subsp. akhurstii FRG04T and 96.8 % with P. luminescens subsp. hainanensis C8404T. The fatty acid profile of the strain consisted of the major fatty acids C14 : 0, C16 : 0, C17 : 0 cyclo, C16 : 1ω7c and/or iso-C15 : 0 2-OH, and C18 : 1ω7c. The MLSA results and the differential biochemical and chemotaxonomic properties showed that strain PB45.5T represents a novel P. luminescens subspecies, for which the name Photorhabdus luminescens subsp. namnaonensis subsp. nov. (type strain PB45.5T=LMG 29915T=CCM 8729T) is proposed.

Strains of Photorhabdus spp. associated with polish Heterorhabditis isolates: their molecular and phenotypic characterization and symbiont exchange

The relationships between six bacterial symbionts of the entomopathogenic nematodes Heterorhabditis bacteriophora and Heterorhabditis megidis from Poland to species and subspecies of the genus Photorhabdus were evaluated. This study was based on phylogenetic analysis of sequence data of five genes: 16S rRNA, gyrB, recA, gltX, and dnaN. The bacteria were also characterized phenotypically by biochemical and physiological tests. Our results have revealed that the Photorhabdus strains isolated from H. megidis belong to P. temperata, subsp. temperata and subsp. cinerea. Isolates from H. bacteriophora represent P. luminescens subs. kayaii and P. temperata subs. cinerea. This study for the first time provides evidence for H. bacteriophora and P. temperata subsp. cinerea symbiotic association. In addition, we tested whether the microsymbionts of the Polish H. bacteriophora and H. megidis isolates support the development of non-native nematode host population and colonization of their infective juveniles. It has been shown that the studied Photorhabdus strains can readily swap their nematode host, both at intra- and interspecies level. It supports the hypothesis of different symbiotic associations in the Heterorhabditis-Photorhabdus lineage.

First Report of the Isolation of the Symbiotic Bacterium Photorhabdus luminescens subsp. laumondii Associated with Heterorhabditis safricana from South Africa

Photorhabdus luminescens subsp. laumondii is closely associated with the entomopathogenic nematode Heterorhabditis bacteriophora and has, to date, not been isolated from other nematode species. This study is the first report of P. luminescens subsp. laumondii from two South African isolates of entomopathogenic nematodes, Heterorhabditis safricana SF281 and H. bacteriophora SF351. Both symbiotic bacterial strains are phenotypically closely related to P. luminescens subsp. laumondii previously isolated and described from H. bacteriophora. The genetic relatedness between P. luminescens subsp. laumondii strains SF281B and SF351B was confirmed by comparing 16S rDNA, recA, gyrB and gltX sequences with sequences of P. luminescens subsp. laumondii, including the type strain (TT01^T) and strain E21.

First report of the symbiotic bacterium Xenorhabdus indica associated with the entomopathogenic nematode Steinernema yirgalemense

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.

Photorhabdus heterorhabditis sp. nov., a symbiont of the entomopathogenic nematode Heterorhabditis zealandica

The bacterial symbionts SF41T and SF783 were isolated from populations of the insect pathogenic nematode Heterorhabditis zealandica collected in South Africa. Both strains were closely related to strain Q614 isolated from a population of Heterorhabditis sp. collected from soil in Australia in the 1980s. Sequence analysis based on a multigene approach, DNA-DNA hybridization data and phenotypic traits showed that strains SF41T, SF783 and Q614 belong to the same species of the genus Photorhabdus with Photorhabdus temperata subsp. cinerea as the most closely related taxon (DNA-DNA hybridization value of 68%). Moreover, the phylogenetic position of Photorhabdus temperata subsp. cinerea DSM 19724T initially determined using the gyrB sequences, was reconsidered in the light of the data obtained by our multigene approach and DNA-DNA hybridization experiments. Strains SF41T, SF783 and Q614 represent a novel species of the genus Photorhabdus, for which the name Photorhabdus heterorhabditis sp. nov. is proposed (type strain SF41T=ATCC BAA-2479T=DSM 25263T).

Description of Xenorhabdus khoisanae sp. nov., the symbiont of the entomopathogenic nematode Steinernema khoisanae

Bacterial strain SF87(T), and additional strains SF80, SF362 and 106-C, isolated from the nematode Steinernema khoisanae, are non-bioluminescent Gram-reaction-negative bacteria that share many of the carbohydrate fermentation reactions recorded for the type strains of recognized Xenorhabdus species. Based on 16S rRNA gene sequence data, strain SF87(T) is shown to be closely related (98% similarity) to Xenorhabdus hominickii DSM 17903(T). Nucleotide sequences of strain SF87 obtained from the recA, dnaN, gltX, gyrB and infB genes showed 96-97% similarity with Xenorhabdus miraniensis DSM 17902(T). However, strain SF87 shares only 52.7% DNA-DNA relatedness with the type strain of X. miraniensis, confirming that it belongs to a different species. Strains SF87(T), SF80, SF362 and 106-C are phenotypically similar to X. miraniensis and X. beddingii, except that they do not produce acid from aesculin. These strains are thus considered to represent a novel species of the genus Xenorhabdus, for which the name Xenorhabdus khoisanae sp. nov. is proposed. The type strain is SF87(T) ( =DSM 25463(T) =ATCC BAA-2406(T)).