Dissecting the invasion of Galleria mellonella by Yersinia enterocolitica reveals metabolic adaptations and a role of a phage lysis cassette in insect killing

Abstract

The human pathogen Yersinia enterocolitica strain W22703 is characterized by its toxicity towards invertebrates that requires the insecticidal toxin complex (Tc) proteins encoded by the pathogenicity island Tc-PAIYe. Molecular and pathophysiological details of insect larvae infection and killing by this pathogen, however, have not been dissected. Here, we applied oral infection of Galleria mellonella (Greater wax moth) larvae to study the colonisation, proliferation, tissue invasion, and killing activity of W22703. We demonstrated that this strain is strongly toxic towards the larvae, in which they proliferate by more than three orders of magnitude within six days post infection. Deletion mutants of genes tcaA and tccC were atoxic for the insect. W22703 delta tccC, in contrast to W22703 delta tcaA, initially proliferated before being eliminated from the host, thus confirming TcaA and TccC as membrane-binding Tc subunit and ADP-ribosylating enzyme, respectively. Time course experiments revealed a Tc-dependent infection process starting with midgut colonisation that is followed by invasion of the hemolymph where the pathogen elicits morphological changes of hemocytes and strongly proliferates. The in vivo transcriptome of strain W22703 shows that the pathogen undergoes a drastic reprogramming of central cell functions and gains access to numerous carbohydrate and amino acid resources within the insect. Strikingly, a mutant lacking a phage-related holin/endolysin (HE) cassette, which is located within Tc-PAIYe, resembled the phenotypes of W22703 delta tcaA, suggesting that this dual lysis cassette is an example for a phage-related function that has been adapted for the release of a bacterial toxin.

Specialized pathogenic cells release Tc toxins using a type 10 secretion system

“…S13a-d), indicating that these bacteria employ the same secretion mechanism as Y. entomophaga. Although the presence of a T10SS in Y. enterocolitica has been noticed before (52), its biological relevance has now been validated by demonstrating that without its T10SS this pathogen loses its ability to establish an infection in insects in a manner similar to a Tc toxin deletion mutant (53). Given that our reconstruction of the ancient Y. pestis Tc toxin operon from a Black Death victim (54) shows that it also encodes a T10SS (Fig.…”