LtrB inhibits Vibrio parahaemolyticus motility while promoting biofilm formation and seafood adhesion

Abstract

Vibrio parahaemolyticus is a major seafood-borne pathogen whose ability to form biofilms enhances its persistence in food-processing environments and contributes to its resistance to antimicrobial agents. In this study, we investigated the role of the LysR-type transcriptional regulator LtrB (VPA0388) in coordinating the switch between motility and biofilm formation in V. parahaemolyticus. We demonstrated that LtrB is required for proper biofilm development, extracellular matrix production, and wrinkled colony morphotype formation, while simultaneously repressing both swimming and swarming motility. Mechanistically, we showed that LtrB acts as a direct transcriptional regulator that binds to the promoter regions of multiple genes, including biofilm-matrix genes (cpsA, scvE, cpsQ, mfpA) and flagellar genes (flgM, flgA, flgB, flgK, lafA, fliD), activating the former and repressing the latter. In contrast, the regulation of motY and fliM appears to be indirect, as no binding of LtrB to their promoter regions was detected. Furthermore, LtrB exerts these regulatory effects largely independently of the c-di-GMP signaling pathway, as intracellular c-di-GMP levels remain unaltered upon ltrB deletion. Consistent with its role in promoting a sessile lifestyle, LtrB was required for bacterial adhesion to biotic (mussel and shrimp) and abiotic (glass and stainless steel) surfaces relevant to food production. These findings establish LtrB as a regulator that promotes a sessile, biofilm-forming lifestyle by downregulating motility and upregulating matrix production, thereby facilitating persistent colonization in food-related environments.