Two Regulators of Vibrio parahaemolyticus Play Important Roles in Enterotoxicity by Controlling the Expression of Genes in the Vp-PAI Region

Abstract

Vibrio parahaemolyticus is an important pathogen causing food-borne disease worldwide. An 80-kb pathogenicity island (Vp-PAI), which contains two tdh (thermostable direct hemolysin) genes and a set of genes for the type III secretion system (T3SS2), is closely related to the pathogenicity of this bacterium. However, the regulatory mechanisms of Vp-PAI's gene expression are poorly understood. Here we report that two novel ToxR-like transcriptional regulatory proteins (VtrA and VtrB) regulate the expression of the genes encoded within the Vp-PAI region, including those for TDH and T3SS2-related proteins. Expression of vtrB was under control of the VtrA, as vector-expressed vtrB was able to recover a functional protein secretory capacity for T3SS2, independent of VtrA. Moreover, these regulatory proteins were essential for T3SS2-dependent biological activities, such as in vitro cytotoxicity and in vivo enterotoxicity. Enterotoxic activities of vtrA and/or vtrB deletion strains derived from the wild-type strain were almost absent, showing fluid accumulation similar to non-infected control. Whole genome transcriptional profiling of vtrA or vtrB deletion strains revealed that the expression levels of over 60 genes were downregulated significantly in these deletion mutant strains and that such genes were almost exclusively located in the Vp-PAI region. These results strongly suggest that VtrA and VtrB are master regulators for virulence gene expression in the Vp-PAI and play critical roles in the pathogenicity of this bacterium.

Regulation by ToxR-Like Proteins Converges on vttR B Expression To Control Type 3 Secretion System-Dependent Caco2-BBE Cytotoxicity in Vibrio cholerae

“…Similar conclusions were drawn for the homologous T3SS regulatory proteins in Vibrio parahaemolyticus, VtrA and VtrB, based on data from complementation and electrophoretic mobility shift assays (36,37). Interestingly, when the V. cholerae ⌬vttR A strain was complemented by using vttR B , we observed cytotoxicity using a lower arabinose concentration than that for complementation with pBAD18-vttR A (Fig.…”

Development of Two Animal Models To Study the Function of Vibrio parahaemolyticus Type III Secretion Systems

“…Nevertheless, it has also been shown that mutant strains lacking tdhS and tdhA genes are still able to cause intestinal fluid accumulation in the same model (26). There is also evidence indicating that T3SS2 is an important factor in fluid secretion for ileal-loop models (17,18,27). In the present study, the clinical signs of infected piglets resembled the gastrointestinal presentation of the human disease.…”

“…Nevertheless, because T3SS2 is encoded by genes carried on an 80-kbp pathogenicity island and the genes encoding T3SS2 are flanked by tdhA and tdhS in the pandemic serovar (17), it is possible that the mutation of a T3SS2 structural gene could have polar effects on the synthesis of TDH. This possibility is enhanced on the basis of the fact that we have been unable to complement either of our T3SS1 or T3SS2 deletion mutant strains, probably owing to polar effects within the islands carrying the genes encoding the T3SSs.…”

The Vibrio parahaemolyticus ToxRS Regulator Is Required for Stress Tolerance and Colonization in a Novel Orogastric Streptomycin-Induced Adult Murine Model

“…Vibrio parahaemolyticus contains a ToxRS homologue, but the role ToxRS plays in the pathogenicity of this organism has not been fully elucidated (38,67,68). Data suggesting that ToxRS is involved in regulating TDH expression (38) have been confounded by evidence suggesting that two ToxR-like regulators, vtrA and vtrB (located within VPaI-7), control the levels of TDH expressed in V. parahaemolyticus (33).…”