Insecticidal genes of Yersinia spp.: taxonomical distribution, contribution to toxicity towards Manduca sexta and Galleria mellonella, and evolution

Abstract

<p>Abstract</p> <p>Background</p> <p>Toxin complex (Tc) proteins termed TcaABC, TcdAB, and TccABC with insecticidal activity are present in a variety of bacteria including the yersiniae.</p> <p>Results</p> <p>The <it>tc </it>gene sequences of thirteen <it>Yersinia </it>strains were compared, revealing a high degree of gene order conservation, but also remarkable differences with respect to pseudogenes, sequence variability and gene duplications. Outside the <it>tc </it>pathogenicity island (<it>tc</it>-PAI^<it>Ye</it>) of <it>Y. enterocolitica </it>strain W22703, a pseudogene (<it>tccC2'</it>/<it>3'</it>) encoding proteins with homology to TccC and similarity to tyrosine phosphatases at its C-terminus was identified. PCR analysis revealed the presence of the <it>tc</it>-PAI^{<it>Ye </it>}and of <it>tccC2'</it>/<it>3'</it>-homologues in all biotype 2–5 strains tested, and their absence in most representatives of biotypes 1A and 1B. Phylogenetic analysis of 39 TccC sequences indicates the presence of the <it>tc</it>-PAI^{<it>Ye </it>}in an ancestor of <it>Yersinia</it>. Oral uptake experiments with <it>Manduca sexta </it>revealed a higher larvae lethality of <it>Yersinia </it>strains harbouring the <it>tc</it>-PAI^{<it>Ye </it>}in comparison to strains lacking this island. Following subcutaneous infection of <it>Galleria mellonella </it>larvae with five non-human pathogenic <it>Yersinia </it>spp. and four <it>Y. enterocolitica </it>strains, we observed a remarkable variability of their insecticidal activity ranging from 20% (<it>Y. kristensenii</it>) to 90% (<it>Y. enterocolitica </it>strain 2594) dead larvae after five days. Strain W22703 and its <it>tcaA </it>deletion mutant did not exhibit a significantly different toxicity towards <it>G. mellonella</it>. These data confirm a role of TcaA upon oral uptake only, and suggest the presence of further insecticidal determinants in <it>Yersinia </it>strains formerly unknown to kill insects.</p> <p>Conclusion</p> <p>This study investigated the <it>tc </it>gene distribution among yersiniae and the phylogenetic relationship between TccC proteins, thus contributing novel aspects to the current discussion about the evolution of insecticidal toxins in the genus <it>Yersinia</it>. The toxic potential of several <it>Yersinia </it>spp. towards <it>M. sexta </it>and <it>G. mellonella </it>demonstrated here for the first time points to insects as a natural reservoir for yersiniae.</p