The role of Elongation factor P in the virulence of Shigella flexneri
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Shigella flexneri is a bacterial pathogen which causes dysentery by invading the epithelial cells of the colon. In order to survive and replicate inside the host, S. flexneri requires many genes present on both its chromosome and the large virulence plasmid it carries. This study examines which genes are required for infection of cultured epithelial cells in order to understand which processes are used by S. flexneri during the infection process. This analysis pinpointed genes involved in metabolism, LPS synthesis, protein homeostasis and virulence effector proteins. The role of Elongation factor P (EF-P) in S. flexneri virulence is also investigated in this study. EF-P is a bacterial translation factor that is post-translationally modified with a [Beta]-lysine by the action of PoxA. Here it is shown that both EF-P and PoxA are necessary for virulence of S. flexneri. Loss of either EF-P or PoxA leads to an impaired ability of S. flexneri to invade epithelial cells. Proteomic analysis of efp and poxA deletion mutants revealed decreased levels of several virulence effector proteins, as well as proteins for the biosynthesis of the siderophore aerobactin. Virulence proteins were affected due to decreased levels of the master virulence regulator VirF. Reduction in VirF transcription is likely due to decreased levels of CpxA, which activates virF through the response regulator CpxR. The role of CpxAR in reduced synthesis of VirF and its downstream effectors was confirmed by showing increased invasion when a mutation resulting in constitutively vii activated CpxR was introduced into the efp mutant. Thus, modified EF-P is one of the chromosomal factor necessary for the virulence of this bacterial pathogen.