Environmental Regulation and Virulence Attributes of the Ysa Type III Secretion System of Yersinia enterocolitica Biovar 1B

Abstract

Pathogenic biovars of Yersinia enterocolitica maintain the well-studied plasmid-encoded Ysc type III secretion (TTS) system, which has a definitive role in virulence. Y. enterocolitica biovar 1B additionally has a distinct chromosomal locus, the Yersinia secretion apparatus pathogenicity island (YSA PI) that encodes the Ysa TTS system. The signals to which the Ysa TTS system responds and its role in virulence remain obscure. This exploratory study was conducted to define environmental cues that promote the expression of Ysa TTS genes and to define how the Ysa TTS system influences bacterium-host interactions. Using a genetic approach, a collection of Y. enterocolitica Ysa TTS mutants was generated by mutagenesis with a transposon carrying promoterless lacZYA. This approach identified genes both within and outside of the YSA PI that contribute to Ysa TTS. Expression of these genes was regulated in response to growth phase, temperature, NaCl, and pH. Additional genetic analysis demonstrated that two regulatory genes encoding components of the YsrR-YsrS (ysrS) and RcsC-YojN-RcsB (rcsB) phosphorelay systems affect the expression of YSA PI genes and each other. The collection of Ysa TTS-defective transposon mutants, along with other strains carrying defined mutations that block Ysa and Ysc TTS, was examined for changes in virulence properties by using the BALB/c mouse model of infection. This analysis revealed that the Ysa TTS system impacts the ability of Y. enterocolitica to colonize gastrointestinal tissues. These results reveal facets of how Y. enterocolitica controls the function of the Ysa TTS system and uncovers a role for the Ysa TTS during the gastrointestinal phase of infection.

Synchronous Gene Expression of theYersinia enterocoliticaYsa Type III Secretion System and Its Effectors

“…Previous studies had indicated that several genes within the ysa locus were maximally expressed during early to mid-log phase using ␤-galactosidase reporters (37). However, since reporter data does not always agree with transcript levels, we chose to expand our analysis by examining expression of the ysp genes and related genes over the course of a growth curve by Northern analysis.…”

“…The Ysa T3SS is regulated by the putative phosphorelay proteins YsrS and YsrR that are encoded by genes adjacent to the ysa locus ( Fig. 1) and by the known phosphorelay protein RcsB (37,38). YsrS, a putative hybrid sensor kinase, was shown to activate the ysaE promoter to the same level as NaCl and is hypothesized to sense the NaCl levels (38).…”

“…1). High levels of NaCl in the growth medium induce secretion by the Ysa T3SS (17), and it was subsequently shown that the ysaE promoter was activated by NaCl (37,38). The Ysa T3SS is regulated by the putative phosphorelay proteins YsrS and YsrR that are encoded by genes adjacent to the ysa locus ( Fig.…”

Regulation of bacterial virulence gene expression by cell envelope stress responses

“…In this case RcsB positively regulates expression of the Ysa T3SS-encoding genes, which are found in highly pathogenic biogroup B1 strains and might be important in mammals or insects. [126][127][128] RcsB is involved in activating expression of the ysaE operon, which encodes a master regulator of the ysa locus and structural components of the T3SS. However, the mechanism by which this occurs is unclear and it is not yet known if RcsB binds to the ysaE promoter.…”

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“…SycB also acts as a regulator of T3SS by interacting with the transcriptional activator YsaE and activating the transcription of sycB, yspBCDA. Activation signal of Ysa-Ysp T3SS is mediated by phospho-relay proteins YsrR, YsrS, YsrT, RcsB, where transcriptional regulators YsaE and SycB also play a major role [7,11,12,13,14,15,16]. A narrow conduit is required for translocation of toxic effector proteins from bacterial cell to the host cell cytoplasm.…”