A secondary metabolite acting as a signalling molecule controls Pseudomonas entomophila virulence

Pseudomonas entomophila is an entomopathogenic bacterium that is lethal to Drosophila melanogaster within 1-2 days of ingestion of high doses. Flies orally infected with P. entomophila rapidly succumb despite the induction of both local and systemic immune responses. Recent studies suggest that its virulence relies on its ability to cause irreversible damages to the intestinal epithelium, in contrast to what is observed with milder pathogenic bacteria such as Erwinia carotovora carotovora Ecc15 or Pseudomonas aeruginosa PA14. The GacS/GacA two-component system plays a key role in P. entomophila pathogenicity. Here, we report the identification of the pvf genes, whose products are involved in production of a secondary metabolite involved in P. entomophila virulence. A pvf mutant is impaired in its ability to persist within the gut, to trigger the fly immune responses and to inflict gut damages. The expression of several genes is affected in a pvf mutant, independently of the Gac system. Moreover, growing a pvf mutant in medium supplemented with supernatant extracts from either the wild-type strain or a gacA mutant restore its pathogenicity. Collectively, our results indicate that we identified genes involved in the synthesis of a signalling molecule that controls P. entomophila virulence independently from the Gac system.