Complementation of the exoS gene in the pvdE pyoverdine synthesis gene-deficient mutant of Pseudomonas aeruginosa results in recovery of the pvdE gene-mediated penetration through the intestinal epithelial cell barrier but not the pvdE-mediated virulence in silkworms

Abstract

Translocation of endogenous Pseudomonas aeruginosa from the colonized intestinal tract is an important pathogenic phenomenon. Comparative genome hybridization analysis of high virulent and low virulent strains allowed us to identify bacterial genes that are associated with bacterial translocation from gut in infected hosts. Here we focused on the pvdE pyoverdine synthesis gene among the identified bacterial genes, showing that the pvdE gene is required for bacterial penetration through epithelial cell monolayers and for bacterial translocation from gut to hemolymph in infected silkworms. We next revealed that mRNA expression level of the exoS gene in a pvdE-deficient mutant (ΔpvdE) after incubation with Caco-2 cells was greatly reduced as compared with that in the wild-type strain. The pvdE- and exoS-complemented ΔpvdE strains (ΔpvdE/pvdE and ΔpvdE/exoS) showed recovery of the ability of bacterial penetration through Caco-2 cell monolayers and of the ability of bacterial translocation from gut to hemolymph in infected silkworms. However, there were differences between the ability of ΔpvdE/pvdE and ΔpvdE/exoS to kill silkworms after intestinal infection and to replicate in hemolymph following direct injection into the hemolymph: ΔpvdE/pvdE could kill silkworms after intestinal infection and could replicate in hemolymph to levels similar to those of the wild-type strain, but ΔpvdE/exoS could not. Taken together, our results suggest that the virulence of the wild-strain mediated by the pvdE gene is the result of the ability to both penetrate through the intestinal epithelial cell barrier depending on ExoS and to replicate in hemolymph independently of ExoS.