Submitted to: Society for Invertebrate Pathology Annual Meeting
Publication Type: Abstract only
Publication Acceptance Date: 9/24/2008
Publication Date: 10/15/2008
Citation: Pechy-Tarr, M., Bruck, D.J., Maurhofer, M., Fischer, E., Vogne, C., Grunder, J., Loper, J.E., Keel, C. 2008. A novel gene cluster encoding an insect toxin in plant-associated strains of Pseudomonas fluorescens. Society for Invertebrate Pathology Annual Meeting. Interpretive Summary:
Technical Abstract: Pseudomonas fluorescens CHA0 and the related strain Pf-5 are well-characterized rhizosphere bacteria that have the capacity to protect crop plants from fungal root diseases, mainly by releasing a variety of exoproducts that are toxic to plant pathogenic fungi. Here, we report that the two plant-beneficial pseudomonads exhibit potent insecticidal activity. Anti-insect activity is linked to a novel genomic locus encoding a large protein toxin termed Fit (for P. fluorescens insecticidal toxin) that is related to the insect toxin Mcf (Makes caterpillars floppy) of the entomopathogen Photorhabdus luminescens, a mutualist of entomopathogenic nematodes. When injected into the hemocoel, even low doses of P. fluorescens CHA0 or Pf-5 killed larvae of the tobacco hornworm Manduca sexta and the greater wax moth Galleria mellonella. By contrast, mutants of CHA0 or Pf-5 with deletions in the Fit toxin gene were significantly less virulent to the larvae. When expressed from an inducible promoter in a non-toxic Escherichia coli host, the Fit toxin gene was sufficient to render the bacterium toxic to both insect hosts. Our findings establish the Fit gene products of P. fluorescens CHA0 and Pf-5 as potent insect toxins that define previously unappreciated anti-insect properties of these plant-colonizing bacteria.