Submitted to: Swiss Society of Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 4/17/2008
Publication Date: 6/12/2008
Citation: Pechy-Tarr, M., Bruck, D.J., Fischer, E., Grunder, J., Loper, J.E., Maurhofer, M. 2008. Molecular analysis of a novel gene cluster encoding an insect toxin in plant-associated strains of Pseudomonas. 67th Annual Assembly of the Swiss Society of Microbiology Program Book. Interpretive Summary:
Technical Abstract: The development of sustainable pest management practices that are safe and environmentally benign is a major agricultural goal worldwide. Microbial biological control agents of insect pests or pathogens have been employed successfully towards this goal, but these agents typically fall in two distinct groups that are effective against plant pathogens or insect pests, but not both. Here, we report that two plant-associated strains of Pseudomonas fluorescens, which are known to suppress soil-borne plant diseases, also exhibit potent insecticidal activity due, in part, to their production of a toxin termed Fit (for P. fluorescens insecticidal toxin). Fit is related to the insect toxin Mcf (Makes caterpillars floppy) of the entomopathogen Photorhabdus luminescens, a mutualist of insect-invading 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 Escherichia coli, 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 insecticidal properties of these plant-colonizing bacteria. The capacity of these beneficial strains of P. fluorescens to produce compounds toxic against both plant pathogens and insect pests highlights new possibilities to employ the strains to enhance the health and productivity of agricultural crops.