Molecular analysis of a novel gene cluster encoding an insect toxin in plant-associated strains of Pseudomonas fluorescens.
Pseudomonas fluorescens CHA0 and the related strain Pf-5 are well-characterized representatives of 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 also exhibit potent insecticidal activity. Anti-insect activity is linked to a novel genomic locus encoding a large protein toxin termed Fit (for P. fluorescensinsecticidal toxin) that 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 haemocoel, 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. In 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.
Péchy-Tarr
Maria
M
Department of Fundamental Microbiology, University of Lausanne, CH-1015 Lausanne, Switzerland.
Bruck
Denny J
DJ
Maurhofer
Monika
M
Fischer
Esther
E
Vogne
Christelle
C
Henkels
Marcella D
MD
Donahue
Kelly M
KM
Grunder
Jürg
J
Loper
Joyce E
JE
Keel
Christoph
C
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D001427:Bacterial Toxins / Q000235:genetics*; D002876:Chromosomes, Bacterial / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D015698:Genomic Library; D007814:Larva / Q000382:microbiology; D007928:Lethal Dose 50; D018402:Manduca / Q000382:microbiology; D008969:Molecular Sequence Data; D009036:Moths / Q000382:microbiology; D005810:Multigene Family; D010572:Pest Control, Biological; D010944:Plants / Q000382:microbiology*; D011551:Pseudomonas fluorescens / Q000235:genetics*; D017422:Sequence Analysis, DNA
D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004269:DNA, Bacterial