Enhanced pathogenicity of Vibrio cholerae S15G02 ΔluxS mutant in Procypris rabaudi: AI-2 quorum sensing disruption triggers hypervirulence

Quorum sensing (QS) serves as a crucial bacterial communication mechanism that modulates virulence in multiple aquaculture pathogens. Interfering with QS signals can mitigate pathogenic risks without exerting growth selection pressure, a promising strategy whose implementation requires deeper understanding of pathogen-specific QS-mediated regulatory mechanisms. Although Vibrio cholerae is primarily known as a human pathogen, recent disease outbreaks in aquaculture highlight its emerging threat to industry sustainability. Nevertheless, little is known about its pathogenic mechanisms in natural fish hosts, particularly regarding QS-mediated virulence regulation. Here, we documented a V. cholerae outbreak in farmed Procypris rabaudi from a recirculating aquaculture system in Chongqing, China. 16S rRNA gene sequencing revealed Vibrio as the dominant bacterium in the livers of diseased fish (relative abundance >95.45 %), leading to the isolation of a V. cholerae , designated S15G02, with a median lethal dose (LD 50 ) of 2.94 × 10 4 CFU/g via intraperitoneal challenge. Infection resulted in rapid systemic dissemination and severe histopathological damage in the liver, kidney, spleen, gills, and intestine. Histopathological analysis and qRT-PCR confirmed severe tissue damage and an inflammatory burst in moribund fish. To investigate the role of AI-2-based QS, we constructed a Δ luxS mutant and its complemented strain Δ luxS :: luxS . The results demonstrated that loss of luxS , which encodes the AI-2 synthase, led to reduced growth, increased antibiotic susceptibility, enhanced biofilm formation and elevated virulence and transmission capacity. These findings reveal a phenomenon in V. cholerae S15G02: disruption of AI-2 synthesis enhances rather than attenuates pathogenicity. Our study elucidates pathogenic mechanisms of V. cholerae in farmed P. rabaudi and provides new insights for precise QS-targeted control of aquatic vibriosis. • 16S rRNA gene sequencing revealed a Vibrio -dominated bacterial community in diseased Procypris rabaudi . • The causative agent, Vibrio cholerae strain (S15G02), showed an LD₅₀ of 2.94 × 10 4 CFU/g in experimental challenge. • LuxS knockout increased virulence and transmission of strain S15G02. • The Δ luxS mutant showed pleiotropy: reduced growth, higher antibiotic susceptibility, and enhanced biofilm.