Abstract
BackgroundToxin complex (Tc) proteins termed TcaABC, TcdAB, and TccABC with insecticidal activity are present in a variety of bacteria including the yersiniae.ResultsThe tc gene sequences of thirteen Yersinia 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 tc pathogenicity island (tc-PAIYe) of Y. enterocolitica strain W22703, a pseudogene (tccC2'/3') encoding proteins with homology to TccC and similarity to tyrosine phosphatases at its C-terminus was identified. PCR analysis revealed the presence of the tc-PAIYe and of tccC2'/3'-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 tc-PAIYe in an ancestor of Yersinia. Oral uptake experiments with Manduca sexta revealed a higher larvae lethality of Yersinia strains harbouring the tc-PAIYe in comparison to strains lacking this island. Following subcutaneous infection of Galleria mellonella larvae with five non-human pathogenic Yersinia spp. and four Y. enterocolitica strains, we observed a remarkable variability of their insecticidal activity ranging from 20% (Y. kristensenii) to 90% (Y. enterocolitica strain 2594) dead larvae after five days. Strain W22703 and its tcaA deletion mutant did not exhibit a significantly different toxicity towards G. mellonella. These data confirm a role of TcaA upon oral uptake only, and suggest the presence of further insecticidal determinants in Yersinia strains formerly unknown to kill insects.ConclusionThis study investigated the tc 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 Yersinia. The toxic potential of several Yersinia spp. towards M. sexta and G. mellonella demonstrated here for the first time points to insects as a natural reservoir for yersiniae.
Highlights
Toxin complex (Tc) proteins termed TcaABC, TcdAB, and TccABC with insecticidal activity are present in a variety of bacteria including the yersiniae
The toxin complex (Tc) proteins whose insecticidal potential resembles that of the Bacillus thuringiensis Bt-toxin were first purified from Photorhabdus luminescens which lives in symbiosis with nematodes [1]
Further DNA fragments encoding insecticidal toxins were detected in the genomes of two Y. enterocolitica strains W22703 and T83 [5,6], and on a plasmid of Y. frederiksenii strain 49 [4]
Summary
Toxin complex (Tc) proteins termed TcaABC, TcdAB, and TccABC with insecticidal activity are present in a variety of bacteria including the yersiniae. The toxin complex (Tc) proteins whose insecticidal potential resembles that of the Bacillus thuringiensis Bt-toxin were first purified from Photorhabdus luminescens which lives in symbiosis with nematodes [1]. They have been identified in other insect-parasitizing bacteria such as Serratia entomophila, Xenorhabdus nematophilus, or Pseudomonas entomophila [2,3]. Homologous insecticidal toxin genes are present in most genomes of Yersinia strains sequenced so far, including Y. mollaretii, seven Yersinia pestis strains and three Y. pseudotuberculosis strains They have been found in Y. frederiksenii and in two Y. enterocolitica strains, T83 and W22703, for which a genome sequence is not yet available [4,5,6]. Tc proteins of three Serratia species and of Y. frederiksenii are plasmid-encoded, indicating that these sepABC-like genes are part of a horizontally mobile region [4]
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