Transcriptionnal analysis of a Photorhabdus luminescens TT01 variant, named VAR*, which is a colonial and phenotypic variant displaying delayed pathogenicity in the insect, Spodoptera littoralis.

Photorhabdus luminescens lives in a mutualistic association with entomopathogenic nematodes and is pathogenic for insects. Variants of Photorhabdus frequently arise. VAR* is a colonial and phenotypic variant displaying delayed pathogenicity in 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, TT01alpha. A P. luminescens microarray was used to determine changes in transcript profiles in the exponential and stationary phase growth phase of VAR* and TT01alpha grown in LB broth. Direct transcriptomic comparisons were carried out between VAR* and TT01alpha grown in LB broth. RNA were extracted from bacterial cells in the exponential growth phase (6-hour-old culture, 5 x 107 cfu/ml) and stationary phase (45-hour-old culture, 5 x 108 cfu/ml). Each microarray comparison (TT01alpha versus VAR* growth in exponential growth or stationary phase) included six slides, with three dye-swapping replicates. Each microarray comparison is done twice with two independant biological extractions (repbiol1 or 2).