Phylogenetic position of Fit insect toxin producing pseudomonads

Fit produced by Pseudomonas fluorescens CHA0 is a novel insect toxin in root colonizing pseudomonads, of which a homologue is described in Photorhabdus species.However, occurrence and abundance of insect pathogenicity in plant-associated pseudomonads is still unclear. An extensive screening outside the P. fluorescens complex identified strains of Pseudomonas chlororaphis as further Fit toxin producing candidates. Sequences of five different P. chlororaphis strains generated in this study were used to reconstruct the evolutionary history of the Fit toxin gene and to analyse its mode of evolution. We found that P. chlororaphis is closely associated with a small subgroup of 2,4-diacetylphloroglucinol and pyoluteorin- producing pseudomonads, both when analyzing four housekeeping genes and the nucleotide sequences for the Fit toxin gene. Additionally, we identified purifying selection to be the predominant mode of Fit toxin evolution.