T3SS1 accessory protein gene vscW alters motility, biofilm formation, outer membrane homeostasis, and virulence in Vibrio parahaemolyticus.

Vibrio parahaemolyticus is a Gram-negative pathogen widely distributed in marine environments and can cause infections in humans and aquatic animals. Type III secretion system 1 (T3SS1) accessory protein VscW is homologous to YscW from Yersinia, which contributes to the stability of the T3SS outer membrane secretin YscC and facilitates its oligomerization and localization to the outer membrane. However, the specific function of vscW in V. parahaemolyticus remains poorly understood. In this study, a vscW deletion mutant (ΔvscW-P2C) was constructed by homologous recombination. Compared with the wild-type strain (WT-P2C), ΔvscW-P2C exhibited 41.1% and 45.0% reductions in swimming motility and biofilm formation, respectively. N-phenyl-1-naphthylamine (NPN) fluorescence intensity increased by 60.7% in ΔvscW-P2C, indicating enhanced outer membrane permeability. Pathogenicity examination showed that the cumulative mortality of Litopenaeus vannamei decreased from 66.7% to 41.7% after deletion of the vscW gene, representing an approximate 37.5% reduction in mortality. Proteomic analysis identified 243 differentially expressed proteins, mainly involving T3SS-associated proteins (VscC and VopB), T6SS-associated proteins (Hcp, VgrG, VasG, ImpC, and ImpL), c-di-GMP-associated proteins (GGDEF and EAL-domain-containing proteins), biofilm-associated proteins (VpsT-like, GlnA, and GST), motility- and chemotaxis-associated proteins (FliC and MCP), and putative virulence-associated proteins (PAAR-like-AHH, TcpQ, and VesC). Together, these phenotypic and proteomic findings suggest that vscW deletion is associated with alterations in T3SS1 and other virulence-related functional networks. Collectively, our findings support a contribution of VscW to virulence-associated phenotypes and pathogenicity in V. parahaemolyticus and provide a basis for further investigation of the underlying regulatory mechanisms.