Mutualism and pathogenesis in Xenorhabdus and Photorhabdus: two roads to the same destination

Goodrich-Blair, Heidi; Clarke, David J.

doi:10.1111/j.1365-2958.2007.05671.x

Cited by 276 publications

(241 citation statements)

References 74 publications

(103 reference statements)

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“…Though growth phase impacts virulence, the total number of cells injected appears to be less important 16 , with typical inocula ranging from 20 to 20,000 CFU. In fact, in the case of Xenorhabdus and Photorhabdus species, as few as 5 CFU are sufficient to kill the insect host 17 . In order to assess the virulence properties of bacterial species that are resistant to ethanol sterilization (e.g.…”

Section: Discussionmentioning

confidence: 99%

Rearing and Injection of Manduca sexta Larvae to Assess Bacterial Virulence

Hussa

Goodrich-Blair

2012

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Manduca sexta, commonly known as the tobacco hornworm, is considered a significant agricultural pest, feeding on solanaceous plants including tobacco and tomato. The susceptibility of M. sexta larvae to a variety of entomopathogenic bacterial species [1][2][3][4][5] , as well as the wealth of information available regarding the insect's immune system [6][7][8] , and the pending genome sequence 9 make it a good model organism for use in studying host-microbe interactions during pathogenesis. In addition, M. sexta larvae are relatively large and easy to manipulate and maintain in the laboratory relative to other susceptible insect species. Their large size also facilitates efficient tissue/hemolymph extraction for analysis of the host response to infection.The method presented here describes the direct injection of bacteria into the hemocoel (blood cavity) of M. sexta larvae. This approach can be used to analyze and compare the virulence characteristics of various bacterial species, strains, or mutants by simply monitoring the time to insect death after injection. This method was developed to study the pathogenicity of Xenorhabdus and Photorhabdus species, which typically associate with nematode vectors as a means to gain entry into the insect. Entomopathogenic nematodes typically infect larvae via natural digestive or respiratory openings, and release their symbiotic bacterial contents into the insect hemolymph (blood) shortly thereafter 10 . The injection method described here bypasses the need for a nematode vector, thus uncoupling the effects of bacteria and nematode on the insect. This method allows for accurate enumeration of infectious material (cells or protein) within the inoculum, which is not possible using other existing methods for analyzing entomopathogenesis, including nicking 11 and oral toxicity assays 12 . Also, oral toxicity assays address the virulence of secreted toxins introduced into the digestive system of larvae, whereas the direct injection method addresses the virulence of wholecell inocula.The utility of the direct injection method as described here is to analyze bacterial pathogenesis by monitoring insect mortality. However, this method can easily be expanded for use in studying the effects of infection on the M. sexta immune system. The insect responds to infection via both humoral and cellular responses. The humoral response includes recognition of bacterial-associated patterns and subsequent production of various antimicrobial peptides 7 ; the expression of genes encoding these peptides can be monitored subsequent to direct infection via RNA extraction and quantitative PCR 13 . The cellular response to infection involves nodulation, encapsulation, and phagocytosis of infectious agents by hemocytes 6 . To analyze these responses, injected insects can be dissected and visualized by microscopy 13,14 . Video LinkThe video component of this article can be found at

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Section: Discussionmentioning

confidence: 99%

Rearing and Injection of Manduca sexta Larvae to Assess Bacterial Virulence

Hussa

Goodrich-Blair

2012

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“…Before the IJ stage, a low number of Photorhabdus and Xenorhabdus cells colonize their respective hosts using different processes 54 ; these bacteria reproduce inside the host to produce a mature population of 50-150 colony forming units per IJ. After entering an insect, IJs migrate to the haemolymph, where they release their bacterial symbionts.…”

Section: Box 2 | Insect Immune Responsementioning

confidence: 99%

Bacterial strategies to overcome insect defences

2008

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| Recent genetic and molecular analyses have revealed how several strategies enable bacteria to persist and overcome insect immune defences. Genetic and genomic tools that can be used with Drosophila melanogaster have enabled the characterization of the pathways that are used by insects to detect bacterial invaders and combat infection. Conservation of bacterial virulence factors and insect immune repertoires indicates that there are common strategies of host invasion and pathogen eradication. Long-term interactions of bacteria with insects might ensure efficient dissemination of pathogens to other hosts, including humans. R E V I E W S302 | APRIL 2008 | voLUME 6 www.nature.com/reviews/micro

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“…Finally, as we mentioned above, symbiont transmission to new generations varies widely in the few taxa where it has been studied from > 95% to 10% (Cowles, 2008). Together, these findings reveal that Steinernema and Heterorhabditis are highly adapted to entomopathogeny and showcase adaptations likely to emerge as a result of long-term commitment to the entomopathogenic lifestyle, even though the biological basis for their symbiotic association with bacteria differs significantly (Chaston, 2010 andGoodrich-Blair, 2007). The exceptions and differences that have been observed for these entire hallmark characteristics highlight why specializations should not be used to exclude newly described associations, and emphasize that applying observations from a few representative members to whole clades can be problematic.…”

Section: Characteristics Of Epnsmentioning

confidence: 71%

Entomopathogenic nematode as a biocontrol agent – Recent trends – A Review

Chitra¹,

Sujatha²,

Jeyasankar³

2017

Int. J. Adv. Res. Biol. Sci

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Safety and environmentalcal insecticide issues surrounding the use of chemical insecticides has led to an emphasis on developing alternative control measures such as entomopathogens and their products. Entomopathogenic nematodeare effective biopesticide which can be incorporated in IPM programs because they are considered non-toxic to humans, relatively specific to their target pests and can be applied with standard pesticide equipment. Entomopthogenic nematodes have proven to be the most effective as biological control organisms. Entomopathogenic nematodes have been released extensively in crop fields with negligible effects on non target insects and are regarded as exceptionally safe to the environment. Our focus in this paper was to review mechanism and pathogencity of nematode, phylogeny of nematode for Steinernematidae and Heterorhabditidae. Steinernematidae is represented by the genera Steinernema and Neosteinernema and Heterorhabditidae is represented by the genus Heterorhabditis. They are associated with mutualistic bacteria in the genus Xenorhabdus for Steinernema and Photorhabdus for Heterorhabditis. Thus, it is a nematode bacterium complex that works together as a biological control unit to kill an insect host by penetrating the host through natural opening and there by releasing the bacterial symbiont which spread and multiply in the haemolymph of the insect pest and kill them by septicemia. Infective juvenile entomopathogenic nematode locate their hosts in soil by means of two strategies-ambusing and crusing. Nematode employs different foraging strategies to locate and infect hosts. Genetic diversity may be lost, or genetic variation may have been limited during collection or lost during importation and rearing. A serious problem for EPNs is founder effect because only a limited number of insect cadavers are collected at single geographical sites, resulting in reduced genetic variance. EPNs have been most efficacious in habitats that provide protection from environmental extremes, especially in soil, which is their natural habitat and in cryptic habitats. Excellent control has been archived against plant-boring insects because their cryptic habitats are favorable for nematode survival and infectivity. In developing biocontrol programs using EPNs, one mechanism to increase the chance of success is to screen novel nematode species or strains for potential efficacy against particular target pests.

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Mutualism and pathogenesis in Xenorhabdus and Photorhabdus: two roads to the same destination

Cited by 276 publications

References 74 publications

Rearing and Injection of <em>Manduca sexta</em> Larvae to Assess Bacterial Virulence

Rearing and Injection of <em>Manduca sexta</em> Larvae to Assess Bacterial Virulence

Bacterial strategies to overcome insect defences

Entomopathogenic nematode as a biocontrol agent – Recent trends – A Review

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