Applied and Environmental Microbiology (2011) 77, 1009-1020

A. Lanois, S. Pages, S. Bourot, A.-S. Canoy, A. Givaudan and S. Gaudriault (2011)
Transcriptional analysis of a Photorhabdus sp. variant reveals transcriptional control of phenotypic variation and multifactorial pathogenicity in insects
Applied and Environmental Microbiology 77 (3), 1009-1020
Abstract: Photorhabdus luminescens lives in a mutualistic association with entomopathogenic nematodes and is pathogenic for insects. Variants of Photorhabdus frequently arise irreversibly and are studied because they have altered phenotypic traits that are potentially important for the host interaction. VAR* is a colonial and phenotypic variant displaying delayed pathogenicity when directly injected into the insect, Spodoptera littoralis. In this study, we evaluated the role of transcriptomic modulation in determining the phenotypic variation and delayed pathogenicity of VAR* with respect to the corresponding wild-type form, TT01-alpha. A P. luminescens microarray identified 148 genes as differentially transcribed between VAR* and TT01. The net regulator status of VAR* was found to be significantly modified. We also observed in VAR* a decrease in the transcription of genes supporting certain phenotypic traits, such as pigmentation, crystalline inclusion, antibiosis, and protease and lipase activities. Three genes encoding insecticidal toxins (pit and pirB) or putative insecticidal toxins (xnp2) were less transcribed in VAR* than in the TT01-alpha. The overexpression of these genes was not sufficient to restore the virulence of VAR* to the levels of TT01, which suggests that the lower virulence of VAR* does not result from impaired toxemia in insects. Three loci involved in oxidative stress responses (sodA, katE, and the hca operon) were found to be downregulated in VAR*. This is consistent with the greater sensitivity of VAR* to H₂O₂ and may account for the impaired bacteremia in the hemolymph of S. littoralis larvae observed with VAR*. In conclusion, we demonstrate here that some phenotypic traits of VAR* are regulated transcriptionally and highlight the multifactorial nature of pathogenicity in insects.
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Link to article at publishers website
Database assignments for author(s): Alain Givaudan

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
molecular biology - genes

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Spodoptera littoralis
Heterorhabditis bacteriophora/Photorhabdus (entomopathogen)	Spodoptera littoralis