Insecticidal Toxicity of Yersinia frederiksenii Involves the Novel Enterotoxin YacT

The genus comprises 19 species of which three are known as human and animal pathogens. Some species display toxicity toward invertebrates using the so-called toxin complex (TC) and/or determinants that are not yet known. Recent studies showed a remarkable variability of insecticidal activities when representatives of different species (spp.) were subcutaneously injected into the greater wax moth, . Here, we demonstrate that and are highly toxic to this insect. A member of phylogroup 1B killed larvae with injection doses of approximately 38 cells only, thus resembling the insecticidal activity of . The pathogenicity spp. displays toward the larvae was higher at 15°C than at 30°C and independent of the TC. However, upon subtraction of all genes of the low-pathogenic strain W22703 from the genomes of and , we identified a set of genes that may be responsible for the toxicity of these two species. Indeed, a mutant of lacking , a gene that encodes a protein similar to the heat-stable cytotonic enterotoxin (Ast) of , exhibited a reduced pathogenicity toward larvae and altered the morphology of hemocytes. The data suggests that the repertoire of virulence determinants present in environmental species remains to be elucidated.