Quorum sensing signal synthases enhance Vibrio parahaemolyticus swarming motility

Vibrio parahaemolyticus is a significant food-borne pathogen that is found in diverse aquatic habitats. Quorum sensing (QS), a signaling system for cell-cell communication, plays an important role in V. parahaemolyticus persistence. We characterized the function of three V. parahaemolyticus QS signal synthases, CqsA_vp , LuxM_vp , and LuxS_vp , and show that they are essential to activate QS and regulate swarming. We found that CqsA_vp , LuxM_vp , and LuxS_vp activate a QS bioluminescence reporter through OpaR. However, V. parahaemolyticus exhibits swarming defects in the absence of CqsA_vp , LuxM_vp , and LuxS_vp , but not OpaR. The swarming defect of this synthase mutant (termed Δ3AI) was recovered by overexpressing either LuxO_vp ^D47A , a mimic of dephosphorylated LuxO_vp mutant, or the scrABC operon. CqsA_vp , LuxM_vp , and LuxS_vp inhibit lateral flagellar (laf) gene expression by inhibiting the phosphorylation of LuxO_vp and the expression of scrABC. Phosphorylated LuxO_vp enhances laf gene expression in a mechanism that involves modulating c-di-GMP levels. However, enhancing swarming requires phosphorylated and dephosphorylated LuxO_vp which is regulated by the QS signals that are synthesized by CqsA_vp , LuxM_vp , and LuxS_vp . The data presented here suggest an important strategy of swarming regulation by the integration of QS and c-di-GMP signaling pathways in V. parahaemolyticus.