Associated Bacteria

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The symbiotic association of entomopathogenic nematodes with specific bacteria facilitates reproduction (bacteria serve as food) and pathogenicity of the nematodes. Although axenic nematodes (nematodes without bacteria) may occasionally cause host death, they do not generally reproduce. Furthermore, bacteria alone are incapable of penetrating the alimentary tract and cannot independently gain entrance to the host's hemocoel. Thus, nematodes act as vectors to transport the bacteria into a host within which they can proliferate and the bacteria create conditions necessary for nematode survival and reproduction within the insect cadaver. The ventricular portion of the intestine of the steinernematid infective juvenile is specifically modified for storage of symbiotic bacteria and is called an intestinal vesicle (Poinar & Leutenegger 1968, Bird & Akhurst 1983). In the infective stage of heterorhabditid nematodes, symbiotic bacteria are located in the esophagus and in the ventricular portion of the intestine (Poinar et al. 1977). All species of Steinernema are associated with bacteria of the genus Xenorhabdus and all Heterorhabditis nematode species are associated with Photorhabdus bacteria (Boemare et al. 1993). Each nematode species has a specific natural association with only one bacterial species, although any one bacterial species may be associated with more than one nematode species (Akhurst & Boemare 1990). The specificity of association between nematodes and bacteria operates on three levels (Grewal et al. 1997b): provision of factors that enhance infective juvenile recovery from the non-feeding stage (dauer); provision of essential nutrients for the nematode by the bacterium; and retention of the bacterium within the intestine of the non-feeding infective juvenile.
MUTUALISTIC BACTERIA:
Penetrating nematodes inoculate bacteria Xenorhabdus or Photorhabdus spp. for steinernematids and heterorhabditids, respectively into the host. The nematode may appear to be little more than a biological syringe for its associated bacterium. Although parasitic EPN have not severed their nutritional relationship with bacteria, growth and reproduction are dependent upon conditions established in the host cadaver by the bacterium. Bacteria cannot survive in water and soil nor can reach the insect haemocoel on their own. The nematode must carry the bacteria into the hemocoel of an insect host where they multiply rapidly, kill the host by septicemia and serve as an essential food source for the nematode, and the nematodes do not grow and reproduce in the absence of the bacteria (Poinar & Thomas, 1966). Symbiotic bacteria associated with indigenous isolates of H. indica and S. carpocapsae were isolated and characterized (Nagesh et al., 2001). Phase variation has been observed in this group of bacteria. Pathogenic differences are not found between the two phases. Primary form enhances maturity, reproduction and production of antibiotics (Akhurst, 1980 ; 1982). Phase variation is suggested for survival of bacteria as phase I is more susceptible to phage virus (Akhurst & Boemare, 1990). Specificity of bacteria, bacteria-nematode association has been known. Steinernema species reproduce best in the monoxenic culture of their natural symbiont though they can utilize other bacterial species (Akhurst, 1983). Controlled mass culture of bacteria release metabolites that are anti fungal and anti bacterial. Indole derivatives, stilbene derivatives xenorhabdins, xenocoumacins, xeroxodes,and nematophins are bioactive. They inhibit Bacillus subtilis, Staphylococcus epidermidis, S. aureus, Aspergillus fumigatus and A. flavus (Webster et al., 1996). Xenorhabdus nematophilus was found to inhibit Botrytis cinerea, Cerastomella ulmi, C. dryocoetidis, Mucor piriformis, Pythium colaratum, P. ultimum, Penicillium notatum, Rhizoctonia solani, Trichoderma pseudokoningii and Verticillium dahliae and Photorhabdus inhibited Botrytis cinerea, Cerastomella ulmi, C. dryocoetidis, Mucor piriformis, P. coloratum, P. ultimum, Trichoderma pseudokoningii, Verticillium dahliae (Chen et al., 1994).
Following is the list of associated bacteria of Xenorabdus and Photorhabdus
Xenorhabdus species 1. Xenorhabdus beddingii (Akhurst 1986) Akhurst and Boemare 1993 VP Synonym: Xenorhabdus nematophila subsp. beddingii Akhurst 1986
2. Xenorhabdus bovienii (Akhurst 1983) Akhurst and Boemare 1993 VP Synonym: Xenorhabdus nematophila subsp. bovienii Akhurst 1983
3. Xenorhabdus budapestensis Lengyel et al. 2005 VP
4. Xenorhabdus cabanillasii Tailliez et al. 2006 VP
5. Xenorhabdus doucetiae Tailliez et al. 2006 VP
6. Xenorhabdus ehlersii Lengyel et al. 2005 VP
7. Xenorhabdus griffiniae Tailliez et al. 2006 VP
8. Xenorhabdus hominickii Tailliez et al. 2006 VP Strains: 17903T "Xenorhabdus indica"
9. Xenorhabdus innexi Lengyel et al. 2005 VP
10. Xenorhabdus japonica Nishimura et al. 1995 VP
11. Xenorhabdus koppenhoeferi Tailliez et al. 2006 VP
12. Xenorhabdus kozodoii Tailliez et al. 2006 VP
13. Xenorhabdus luminescens Thomas and Poinar 1979 see: Photorhabdus luminescens subsp. luminescens (Thomas and Poinar 1979) Boemare et al. 1993 VP
14. Xenorhabdus luminescens Thomas and Poinar 1979
15. Xenorhabdus luminescens Thomas and Poinar 1979 see:Photorhabdus luminescens (Thomas and Poinar 1979) Boemare et al. 1993 emend. Fischer-Le Saux et al. 1999 VP
16. Xenorhabdus mauleonii Tailliez et al. 2006 VP
17. Xenorhabdus miraniensis Tailliez et al. 2006 VP
18. Xenorhabdus nematophila (Poinar and Thomas 1965) Thomas and Poinar 1979 AL
19. Xenorhabdus nematophila subsp. beddingii Akhurst 1986
20. Xenorhabdus nematophila subsp. beddingii Akhurst 1986 see:Xenorhabdus beddingii (Akhurst 1986) Akhurst and Boemare 1993 VP
21. Xenorhabdus nematophila subsp. bovienii Akhurst 1983
22. Xenorhabdus nematophila subsp. bovienii Akhurst 1983 see:Xenorhabdus bovienii (Akhurst 1983) Akhurst and Boemare 1993 VP
23. Xenorhabdus nematophila subsp. poinarii Akhurst 1983 see:Xenorhabdus poinarii (Akhurst 1983) Akhurst and Boemare 1993 VP
24. Xenorhabdus nematophila subsp. poinarii Akhurst 1983
25. "Xenorhabdus nematophilus subsp. nematophilus " (Poinar and Thomas 1965) Thomas and Poinar 1979
26. Xenorhabdus poinarii (Akhurst 1983) Akhurst and Boemare 1993 VP Synonym:Xenorhabdus nematophila subsp. poinarii Akhurst 1983
27. Xenorhabdus romanii Tailliez et al. 2006 VP
28. Xenorhabdus stockiae Tailliez et al. 2006 VP
29. Xenorhabdus szentirmaii Lengyel et al. 2005 VP
Photorhabdus species
1. Photorhabdus asymbiotica subsp. asymbiotica Fischer-Le Saux et al. 1999 VP
2. Photorhabdus asymbiotica subsp. australis Akhurst et al. 2004 VP
3. Photorhabdus luminescens (Thomas and Poinar 1979) Boemare et al. 1993 emend. Fischer-Le Saux et al. 1999 VP Synonym:Xenorhabdus luminescens Thomas and Poinar 1979
4. Photorhabdus luminescens subsp. akhurstii Fischer-Le Saux et al. 1999 VP
5. Photorhabdus luminescens subsp. kayaii Hazir et al. 2004 VP
6. Photorhabdus luminescens subsp. laumondii Fischer-Le Saux et al. 1999 VP
7. Photorhabdus luminescens subsp. luminescens (Thomas and Poinar 1979) Boemare et al. Xenorhabdus luminescens Thomas and Poinar 1979
8. Photorhabdus luminescens subsp. thracensis Hazir et al. 2004 VP
9. Photorhabdus temperata Fischer-Le Saux et al. 1999 VP

Abstracts
1. Xenorhabdus gen. nov., a Genus of Entomopathogenic, Nematophilic Bacteria of the Family Enterobacteriaceae
GERARD M. THOMAS AND GEORGE 0. POINAR, JR. International Journal of Systematic Bacteriology 29:352-360 (1979 )

ABSTRACT:
A new genus, Xenorhabdus, is created to accommodate large, gram-negative, rod-shaped, facultatively anaerobic, entomopathogenic bacteria which are intimately associated with entomogenous nematodes. The normal habitat of these bacteria is the intestinal lumen of nematodes or the body cavity of host insects into which they have been introduced by the nematodes. The genus is placed in the family Enterobacteriaceae since the bacteria possess most of the important characteristics of this family. Xenorhabdus differs from other genera of Enterobacteriaceae in large cell size, failure to reduce nitrates to nitrites, intimate association with entomogenous nematodes, entomopathogenesis, and immunological characteristics. The type species is Xenorhabdus nematophilus (Poinar and Thomas) comb. nov. (synonym: Achromobacter nematophilus Poinar and Thomas). Xenorhabdus luminescens sp. nov., a bioluminescent, entomopathogenic bacterium isolated from the intestinal lumen of an entomogenous nematode, Heterorhabditis bacteriophora, is also described. In addition to their immunological differences, the two species are dissimilar in that X. luminescens is positive for bioluminescence and catalase activity, whereas X. nematophilus is not. The type strain of X. nematophilus is ATCC 19061, and that of X. luminescens is strain Hb (= ATCC 29999).

2. Morphological and Functional Dimorphism in Xenorhabdus spp., Bacteria Symbiotically-Associated with the Insect Pathogenic Nematodes Neoaplectana and Heterorhabditis.R. J. AKHURST
Journal of General Microbiology 121:303-309 (1980)

ABSTRACT:
Three genera of insect pathogenic nematodes are known to have specific symbiotic associations with bacteria: Neoaplectana spp. and Heterorhabditis spp. are associated with Xenorhabdus spp. (Thomas & Poinar, 1979) and Steinernema kraussei with a Flavobacterium sp. (Mrdcek, 1977). Each species of nematode is associated with a single bacterial species; all Heterorhabditis spp. examined have Xenorhabdus luminescens as the symbiont but each species of Neoaplectana is associated with a different species of bacterium (R. J. Akhurst, unpublished results). The bacterial symbiont is carried monoxenically in the intestine of the non-feeding infective stage of the nematode. The nematode penetrates an insect host and moves to the haemocoel where it voids the bacteria. The bacteria proliferate, kill the host and establish suitable conditions for reproduction of the nematodes by providing nutrients and inhibiting the growth of other bacteria (Poinar & Thomas, 1966). The symbiotic bacteria are also capable of rendering a wide variety of artificial media suitable for nematode reproduction, thus allowing the economical mass production of the nematodes (Bedding, 1976) necessary for the control of insect pests in the field During a study of the bacterial symbionts of many isolates of several species of Neoaplectana and Heterorhabditis from Australia, Europe, New Zealand and North America, I found that all may produce two forms of colony on agar media. The results of an investigation into the significance of and the relationships between the two forms of X. nematophilus, the symbiont of N. feltiae, are presented in this paper.

3. Antibiotic Activity of Xenorhabdus spp., Bacteria Symbiotically Associated with Insect Pathogenic Nematodes of the Families Heterorhabditidae and Steinernematidae. R, J. AKHURST
Journal of General Microbiology 128:3061-3065 (1982)
ABSTRACT:
Insect pathogenic nematodes of the Heterorhabditidae and Steinernematidae are symbiotically associated with bacteria of the genus Xenorhabdus; each species of nematode is associated with a single bacterial species (Thomas & Poinar, 1979 ; Akhurst, 1982). The bacterial symbiont is carried monoxenically within the intestine of the non-feeding infective stage nematode. After entering the insect host, the infective nematode invades the haemocoel where it releases the bacteria. The bacteria proliferate, kill the insect and enhance conditions for reproduction of the nematodes by providing nutrients and inhibiting the growth of other bacteria (Poinar & Thomas, 1966). Xenorhabdus species produce two forms of colony on agar media (Akhurst, 1980). The two forms of the symbiont of Neoaplectana feltiae can be distinguished by some biochemical tests and differ in their ability to enhance nematode reproduction in vivo and in vitro. The form isolated from the infective nematode (the primary form) was unstable, producing the secondary form which could revert to the primary. No evidence for the presence of bacteriophage or plasmid causing the differences between the forms could be detected. Dutky (1964) suggested that the bacterial symbiont of the DD 136 strain of N. feltiae (=carpocapsae) produced a wide spectrum antibiotic. Poinar et at. (1980) found that both Xenorhabdus nematophilus and X. luminescens inhibited Bacillus cereus subsp. mycoides and B. subtilis. They also reported the presence of defective bacteriophage in X. nematophilus and X. luminescens cultures and suggested that the defective phage was the bacterial agent. This paper presents the results of a study of the range activity and of some properties of the antibiotic produced by Xenorhabdus spp.

4. Taxonomic Study of Xenorhabdus, a Genus of Bacteria Symbiotically Associated with Insect Pathogenic Nematodes
RAYMOND J. AKHURST
International Journal of Systematic Bacteriology 33:38-45 (1983)

ABSTRACT:
The taxonomy of the bacteria symbiotically associated with the insect-pathogenic nematodes Neoaplectana and Heterorhabditis was examined. The bacteria studied were isolated from 33 populations obtained from Australasia, Europe, and the United States. The symbionts of all species of Neoaplectana and Heterorhabditis examined were members of the genus Xenorhabdus, but they differed in several respects from the description of the genus Xenorhabdits, including the guanine-plus-cytosine content of the deoxy ribosome nucleic acid acid and the production of acid from carbohydrates. All bacteria isolated from Heterorhabditis spp. were identified as members of Xenorhabdus luminescens. The bacteria isolated from one Neoaplectana species were similar and were distinguishable from the bacteria isolated from other Neoaplectana species. The following three subspecies of Xenorhabdus nematophilus are proposed: Xenorhabdus nematophilus subsp. nematophilus (bacteria symbiotic with Neoaplectana feltiae (= Neoaplectana carpocapsae); type strain ATCC 19061), Xenorhabdus nematophilus subsp. bovienii (bacteria symbiotic with Neoaplectana bibionis; type strain, UQN1 2210T), and Xenorhabdus nematophilus subsp. poinarii (bacteria symbiotic with Neoaplectana glaseri; type strain, UQM 2216). These subspecies vary in host nematode, pigmentation, maximum temperature for growth, responses to tests for phenylalanine deaminase by secondary-form isolates and for lipase (Tween 80 test) and lecithinase by primary-form isolates, and coloration of primary-form isolates on MacConkey agar and media containing brornthymol blue.

5. A Numerical Taxonomic Study of the Genus Xenorhabdus (Enterobacteriaceae) and Proposed Elevation of the Subspecies of X. nematophilus to Species. R. J. AKHURST AND N. E. BOEMARE
Journal of General Microbiology 134:1835-1845 (1988)
ABSTRACT:
Xenorhabdus spp. are bacteria mutualistically associated with entomopathogenic nematodes of the families Steinernematidae and Heterorhabditidae (Thomas & Poinar, 1979; Akhurst, 1983). The bacteria are pathogenic for the insect host when released into the haemolymph by the nematodes. They support nematode reproduction by producing nutrients and antimicrobial agents that inhibit the growth of a wide range of organisms (Poinar & Thomas, 1966; Akhurst, 1982). All Xenorhabdus isolates have been shown to produce two colony forms when cultured in vitro. These colony forms are indicative of two phases that differ in some biochemical characteristics (Akhurst 1980, 1986; Boemare & Akhurst, 1988). Field-collected infective-stage nematodes carry only primary-phase Xenorhabdus in their intestine. This phase is unstable in vitro, and occasionally in vivo, producing the secondary phase; this may also be unstable, reverting to the primary phase. There has been some difficulty in describing the taxonomic characteristics of Xenorhabdus, with various workers presenting conflicting data (Poinar et al., 1971 ; Thomas & Poinar, 1979, 1983; Akhurst, 1982, 1983; Boemare, 1983; Farmer, 1984; Grimont et al., 1984). Boemare & Akhurst (1988) suggested that one of the reasons for the disparity in results may have been the phase variation. They tested both phases of Xenorhabdus isolated from 21 strains (13 species) of Steinernematidae and Heterorhabditidae for 240 characters to examine the consequence of phase variation on the taxonomy of Xenorhabdus. This paper reports numerical analyses of the data of Boemare & Akhurst (1988). The analyses were undertaken to examine more closely the significance of phase variation for the taxonomy of Xenorhabdus and to evaluate taxonomic relationships within the genus.

6. Lysogeny and Bacteriocinogeny in Xenorhabdus nematophilus and Other Xenorhabdus spp. N. E. BOEMARE," M.-H. BOYER-GIGLIO,'J.-O. THALER,' R. J. AKEURST,'AND M. BREHELIN'
Applied and Environmental Microbiology 58:3032-3037 (1992)
ABSTRACT:
Xenorhabdus spp. (members of the family Enterobacteriaceae) are symbiotically associated with entornopathogenic nematodes in the family’s Steinernematidae and Heterorhabditidae. The nematodes act as vectors, transporting their bacterial symbionts; into the hemocoel of the insect host. Xenorhabdus spp. contribute to the symbiotic relationship by providing nutritional requirements for their nematode partners. Xenorhabdus strains spontaneously produce two colony form variants which have been called phase variants. Phase 1 variants adsorb dyes on agar plates, produce lecithinase, emit light (in bioluminescent strains only and have cytoplasmic paracrystalline inclusions, while these properties are either absent or greatly reduced in phase 2 . Phase 1 variants also produce nonprotein agardiffusible antibiotics that minimize the secondary invasion of the insect cadaver by other microorganisms, while phase 2 variants produce no such compounds. Some of these antibiotics have been identified as indole derivatives, trans-stilbenes, xenorhabdins, and xenocoumacins. Antibiotic activity has also been attributed to elements like the phage tails that were detected in Xenorhabdus luminescens. These elements, interpreted as virulent for Bacillus cereus, were designated defective bacteriophages. Subsequently, a bacteriophage that was lytic for phase 1 but not for phase 2 of X. luminescens was reported. It has been hypothesized that this phage was the cause of phase variation in Xenorhabdus spp.. However, the lytic activity of this phage occurred without any induction, indicating that the phage may have originated from another host. To test the hypothesis that lysogenic phages; were present in Xenorhabdus spp., we attempted to induce lysis by several treatments and determine the nature of the elements causing lysis.

7. DNA Relatedness between Xenorhabdus spp. (Enterobacteriaceae), Symbiotic Bacteria of Entomopathogenic Nematodes, and a Proposal to transfer Xenorhabdus luminescens to a New Genus, Photorhabdus gen. nov.
N. E. BOEMARE, R. J. AKHURST, AND R. G. MOURANT
International Journal of Systematic Bacteriology 43:249-255 (1993)

ABSTRACT:
The genus Xenorhabdus (Enterobacteriaceae) consists almost entirely of the bacterial symbionts of entomopathogenic nematodes belonging to the families Steinernematidae and Heterorhabditidae . The bacterial symbionts are carried monoxenically in a special vesicle in the infective stage (L3 juveniles) of members of the Steinernematidae and throughout the whole intestine of infective juveniles Heterorhabditidae, which provide protection and trans port for their bacterial symbionts. The nematodes also provide protection for their symbionts against the host's immune response; during the early stage of the infection, L4 and adult steinernernatids produce an inhibitor of the insect inducible immune protein. Both nematodes and Xenorhabdus spp. are pathogenic for most insects when they are released into the hemolymph. The bacterial symbionts also contribute to the symbiotic relationship by establishing and maintaining suitable conditions for nematode reproduction, providing nutrients and antimicrobial substances that inhibit the growth of a wide range of micro organisms . Phase variants of 21 strains of Xenorhabdus spp. from 14 nematode species isolated from various parts of the world were characterized biochemically and physiologically, and the data were analyzed by numerical taxonomy. On the basis of this evidence, the elevation of four subspecies of Xenorhabdus nematophilus to species status as X. nematophilus, Xenorhabdus bovienii, Xenorhabdus poinarii, and Xenorhabdus beddingii was proposed, and an emended description of the species Xenorhabdus luminescens was given.

8. Bacteriocinogenesis cells of Xenorhabdus nematophilus and Photorhabdus luminescens: Enterobacteriaceae associated with entomopathogenic nematodes. Stephen Baghdiguian, Marie-Helene Boyer-Giglio, Jacques-Olivier Thaler, Guy Bonnot, Noel Boemare
Biology of the cell 79:177-185 (1993)
ABSTRACT:
The genus Xenorhabdus consists of specific bacterial symbionts of the entornopathogenic nematodes Steinernemat idae, and the genus Photorhabdus consists almost entirely of those of the entornopathogenic nematodes Heterorhabditidae. They are both members of the Enterobacteriaceae. These bacteria are transported by their nematode hosts into the hemocoel of the insect prey, inducing a lethal septiceamia. Moreover, the two bacterial genera contribute to the symbiotic relationship by providing nutritional requirements for their nematode partners during their reproduction in the insect cadavers. Most of the Xenorhabdus strains are lysogenic. They produce few enterphages and a lot of bacteriocins after induction by mitomycin C or high temperature treatments . Consequently, lysogeny was concomitant with an important bacteriocinogeny (as the ability to produce bacteriocins after an induction treatment). They were bactericidal against other species. The term 'bacterio cin' was coined by Jacob et al. for antibacterial agents which were synthetized by bacteria and required specific receptors. Among several types, one group includes phage tail-like particles consisting of contractile tails also called particulate bacteriocins, lethal phages or defective phages . Bacteriocins evidenced in Xenorhabdus cultures belong to this category. They have a high molecular mass, sediment easily and appear as phage tail-like particles in the electron microscope as do numbers of other described contractile tails. Electronic examination of the purified suspensions shows bacteriocins with extended and contracted sheaths.

9. Xenorhabdus and Photorhabdus spp.: Bugs that kill bugs. Forst S., Dowds B., Boemare N., Stackebrandt E.
Annual Review of Microbiology. 51: 47-72 (1997)

ABSTRACT:
Xenorhabdus and Photorhabdus spp. are gram negative gamma proteobacteria that form entomopathogenic symbioses with soil nematodes. They undergo a complex life cycle that involves a symbiotic stage, in which the bacteria are carried in the gut of the nematodes, and a pathogenic stage, in which susceptible insect prey are killed by the combined action of the nematode and the bacteria. Both bacteria produce antibiotics, intracellular protein crystals, and numerous other products. These traits change in phase variants, which arise when the bacteria are maintained under stationary phase conditions in the laboratory. Molecular biological studies suggest that Xenorhabdus and Photorhabdus spp. may serve as valuable model systems for studying signal transduction and transcriptional and posttranscriptional regulation of gene expression. Such studies also indicate that these bacterial groups, which had been previously considered to be very similar, may actually be quite different at the molecular level.

10. PCR-ribotyping of Xenorhabdus and Photorhabdus isolates from the Caribbean region in relation to the taxonomy and geographic distribution of their nematode hosts Fischer-Le-Saux M., Mauléon H., Constant P., Brunel B., Boemare N. Applied and Environmental Microbiology. 64:(11) 4246-4254 (1998)

ABSTRACT:
The genetic diversity of symbiotic Xenorhabdus and Photorhabdus bacteria associated with entomopathogenic nematodes (Steinernema spp. and Heterorhabditis spp.) was examined by a restriction fragment length polymorphism analysis of PCR-amplified 16S rRNA genes (rDNAs). 117 strains were studied, most of which were isolated from the Caribbean basin after exhaustive soil sampling. The collection consisted of 77 isolates recovered from entomopathogenic nematodes on 14 Caribbean islands and of 40 reference strains belonging to Xenorhabdus and Photorhabdus spp. collected at various localities worldwide. 30 distinctive 16S rDNA genotypes were identified, and cluster analysis was used to distinguish the genus Xenorhabdus from the genus Photorhabdus. The genus Xenorhabdus appears more diverse than the genus Photorhabdus, and for both genera the bacterial genotype diversity is in congruence with the host-nematode taxonomy. The occurrence of symbiotic bacterial genotypes was related to the ecological distribution of host nematodes.

11. Isolation and entomotoxic properties of the Xenorhabdus nematophilus F1 lecithinase
Thaler J.O., Duvic B., Givaudan A., Boemare N.
Applied and Environmental Microbiology. 64:(7) 2367-2373 (1998)

ABSTRACT:
Xenorhabdus spp, and Photorhabdus spp,, entomopathogenic bacteria symbiotically associated with nematodes of the families Steinernematidae and Heterorhabditidae, respectively, were shown to produce different lipases when they were grown on suitable nutrient agar, Substrate specificity studies showed that Photorhabdus spp, exhibited a broad lipase activity, while most of the Xenorhabdus spp, secreted a specific lecithinase. Xenorhabdus spp, occur spontaneously in two variants, phase I and phase II. Only the phase I variants of Xenorhabdus nematophilus and Xenorhabdus bovienii strains produced lecithinase activity when the bacteria were grown on a solid lecithin medium (0.01% lecithin nutrient agar; 24 h of growth). Five enzymatic isomers responsible for this activity were separated from the supernatant of a X. nematophilus F1 culture in two chromatographic steps, cation-exchange chromatography and C-18 reverse-phase chromatography. The substrate specificity of the X. nematophilus F1 lecithinase suggested that a phospholipase C preferentially active on phosphatidylcholine could be isolated. The entomotoxic properties of each isomer were tested by injection into the hemocoels of insect larvae. None of the isomers exhibited toxicity with the insects tested, Locusta migratoria, Galleria mellonella, Spodoptera littoralis, and Manduca sexta. The possible role of lecithinase as either a virulence factor or a symbiotic factor is discussed.

12. Boemare-NE; Akhurst-RJ. 1988. Biochemical and physiological characterization of colony form variants in Xenorhabdus spp. (Enterobacteriaceae). Journal-of-General-Microbiology, 134: 3, 751-761.
ABSTRACT:
Primary and secondary form variants of Xenorhabdus isolated from 21 strains (13 species) of entomophilic nematodes in the family’s Steinernematidae and Heterorhabditidae were tested for 240 biochemical and physiological characters. Primary form variants, isolated from the infective stage nematodes, could always be distinguished from the secondary by adsorption of neutral red from MacConkey agar. Lecithinase, antibiotic activity and/or adsorption of bromothymol blue were useful for distinguishing the variants of most strains. The variants of all strains also differed for other characteristics but the distinguishing characteristics varied from strain to strain. The importance of including both variants of each strain and of using appropriate methods in the study of Xenorhabdus taxonomy was demonstrated.

13. Pest management in Horticultural ecosystem vol.8: No.1, pp38-42

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ISOLATION AND CHARACTERIZATION OF.-SYMBIOTIC BACTERIA FROM Heterorhabditis spp. AND Steinernema carpocapsae Weiser M. NAGESH, S. S. HUSSAINI and S. P. SINGH
ABSTRACT:
indigenous isolates of entomopathogenic nematodes Steinernema and Heterorhabditis spp. were used for isolating the symbiotic enterobacteria. The bacterial isolation was done using both surface sterilized infective juveniles of the nematode species and the haemolymph of waxmoth. Galleria mellonella larval cadavers infected with the nematodes. Based on morphology, electron microscopy and culture studies the bacteria isolated from indigenous Steiltemema carpocapsae and Heterorhabditis spp. confirmed to the description of Xenorhabdus and Photorhabdus spp.



14. Pest management in Horticultural ecosystem vol.8: No.1, pp38-42
ISOLATION AND CHARACTERIZATION OF.-SYMBIOTIC BACTERIA FROM Heterorhabditis spp. AND Steinernema carpocapsae Weiser M. NAGESH, S. S. HUSSAINI and S. P. SINGH

ABSTRACT:
Indigenous isolates of entomopathogenic nematodes Steinernema and Heterorhabditis spp. were used for isolating the symbiotic enterobacteria. The bacterial isolation was done using both surface sterilized infective juveniles of the nematode species and the haemolymph of waxmoth. Galleria mellonella larval cadavers infected with the nematodes. Based on morphology, electron microscopy and culture studies the bacteria isolated from indigenous Steiltemema carpocapsae and Heterorhabditis spp. confirmed to the description of Xenorhabdus and Photorhabdus spp.