Résumé
Photorhabdus temperata and Bacillus thuringiensis are entomopathogenic bacteria exhibiting toxicities against different insect larvae. Vegetative Insecticidal Protein Vip3LB is a Bacillus thuringiensis insecticidal protein secreted during the vegetative growth stage exhibiting lepidopteran specificity. In this study, we focused for the first time on the heterologous expression of vip3LB gene in Photorhabdus temperata strain K122. Firstly, Western blot analyses of whole cultures of recombinant Photorhabdus temperata showed that Vip3LB was produced and appeared lightly proteolysed. Cellular fractionation and proteinase K proteolysis showed that in vitro-cultured recombinant Photorhabdus temperata K122 accumulated Vip3LB in the cell and appeared not to secrete this protein. Oral toxicity of whole cultures of recombinant Photorhabdus temperata K122 strains was assayed on second-instar larvae of Ephestia kuehniella, a laboratory model insect, and the cutworm Spodoptera littoralis, one of the major pests of many important crop plants. Unlike the wild strain K122, which has no effect on the larval growth, the recombinant bacteria expressing vip3LB gene reduced or stopped the larval growth. These results demonstrate that the heterologous expression of Bacillus thuringiensis vegetative insecticidal protein-encoding gene vip3LB in Photorhabdus temperata could be considered as an excellent tool for improving Photorhabdus insecticidal activities