Insecticidal Toxicity of Yersinia frederiksenii Involves the Novel Enterotoxin YacT

The genus Yersinia comprises 19 species of which three are known as human and animal pathogens. Some species confer toxicity towards invertebrates using the so-called toxin complex (TC) and/or yet unknown determinants. Recent studies showed a remarkable variability of insecticidal activities when representatives of different Yersinia species (spp.) were subcutaneously injected into the greater wax moth, Galleria mellonella. Here, we demonstrate that Y. intermedia and Y. frederiksenii are highly toxic towards this insect. A member of the Y. enterocolitica phylogroup 1B killed G. mellonella larvae with injection doses of approximately 38 cells only, thus resembling the insecticidal activity of Photorhabdus luminescens. The pathogenicity of Yersinia spp. towards the larvae was higher at 15°C than at 30°C and independent of the TC. Upon subtraction of all genes of the low-pathogenic Y. enterocolitica strain W22703 from the genomes of Y. intermedia and Y. frederiksenii, we identified a set of genes that may be responsible for the toxicity of these two species. Indeed, a Y. frederiksenii mutant lacking yacT, a gene that encodes a protein similar to the cytotonic enterotoxin Ast of Aeromonas hydrophila, exhibited a strongly reduced pathogenicity towards G. mellonella larvae and impairs the morphology of hemocytes. These data suggest that the repertoire of virulence determinants present in environmental Yersinia species remains to be elucidated.