Haemolysins are essential to the pathogenicity of deep-sea Vibrio fluvialis

Vibrio fluvialis is an emerging foodborne pathogen that produces VFH (Vibrio fluvialis hemolysin) and δVFH (delta-Vibrio fluvialis hemolysin). The function of δVFH is unclear. Currently, no pathogenic V. fluvialis from deep sea has been reported. In this work, a deep-sea V. fluvialis isolate (V13) was examined for pathogenicity. V13 was most closely related to V. fluvialis ATCC 33809, a human isolate, but possessed 262 unique genes. V13 caused lethal infection in fish and induced pyroptosis involving activation of the NLRP3 inflammasome, caspase 1 (Casp1), and gasdermin D (GSDMD). V13 defective in VFH or VFH plus δVFH exhibited significantly weakened cytotoxicity. Recombinant δVFH induced NLRP3-Casp1-GSDMD-mediated pyroptosis in a manner that depended on K⁺ efflux and intracellular Ca²⁺ accumulation. δVFH bound several plasma membrane lipids, and these bindings were crucial for δVFH cytotoxicity. Together these results provided new insights into the function of δVFH and the virulence mechanism of V. fluvialis.