Dissection of ToxR-dependent and ToxR-independent stress-regulated pathways in Vibrio parahaemolyticus.

Vibrio parahaemolyticus is a seafood-borne Gram-negative bacteria causing diarrheal diseases in humans world wide. ToxR is a membrane-associated transcriptional factor which plays an important role in acid stress tolerance and regulates the expression of virulence genes including type III secretion system 1 (T3SS1) and type VI secretion system 1 (T6SS1) in V. parahaemolyticus. However, possible mechanisms of ToxR mediating virulence gene expression have not been fully understood. In this study, we demonstrated that ToxR is essential for V. parahaemolyticus to tolerate acid stress by constructing a ToxR deletion mutant (Δ toxR) and its complemented strain (toxR +). Quantitative PCR showed that the expression of toxR was up regulated under acid stress condition. RNA-seq analysis showed that ompU encoding one of outer membrane proteins was dramatically down regulated in Δ toxR. Furthermore, the mutation of ompU also led to a significant reduction in tolerating acid stress indicating that ToxR mediated acid stress through regulating ompU expression. RNA-seq results further confirmed that acid stress condition could alter multiple signaling pathways either depending on ToxR (e.g., quorum sensing, fatty acid metabolism) or independent of ToxR (e.g., biosynthesis of secondary metabolites, microbial metabolism in diverse environment, biosynthesis of antibiotics, biosynthesis of amino acids and carbon metabolism pathways). We also for the first time demonstrated that ToxR positively regulated the expression of T6SS2 gene and the interbacteria killing activity. Our study provides comprehensive understanding of signaling pathways which are regulated by both acid stress and ToxR. [ABSTRACT FROM AUTHOR]