Integration of QsvR into the Quorum Sensing Circuit of Vibrio parahaemolyticus

Vibrio parahaemolyticus, the leading cause of seafood-associated gastroenteritis worldwide, requires the two type-III secretion systems (T3SS1 and T3SS2) and a thermostable direct hemolysin (encoded by tdh1 and tdh2) to infect the small intestine. The tdh genes and the T3SS2 gene cluster constitute an 80-kb pathogenicity island known as Vp-PAI located on the chromosome II. Expression of T3SS1 and Vp-PAI is regulated in a quorum sensing (QS)-dependent manner but lacks the detailed regulatory mechanisms. Herein, we show that three factors (QS regulators AphA and OpaR and novel regulator QsvR) form a complex regulatory network to regulate the T3SS1 and Vp-PAI genes. At a low cell density, the expression of the T3SS1 genes is induced by the direct binding of AphA to the exsBAD-vscBCD operon, while Vp-PAI expression is repressed. At a high cell density (HCD), the bacterium turns off T3SS1 expression by replacing AphA with OpaR, triggering the induction of Vp-PAI. Furthermore, QsvR binds to the regulatory regions of all the tested Vp-PAI genes to activate their transcription at HCD. Taken together, our data highlight how multiple QS regulators contribute to the pathogenicity of V. parahaemolyticus by precisely controlling the expression of major virulence determinants during different stages of infection. Funding Statement: This work was supported by the National Natural Science Foundation of China (grant numbers 31671290 and 81601809) Declaration of Interests: The authors declared that they have no conflicts of interest to this work. Ethics Approval Statement: All the animal experiments were approved by the Committee on Animal Research of the Academy of Military Medical Sciences and carried out per the approved guideline.