Vibrio alginolyticus MviN is a LuxO-regulated protein and affects cytotoxicity toward EPC cell

Vibrio alginolyticus, a gram-negative marine bacterium, is one of the causative agents of fish vibriosis. Its virulence factors and pathogenesis mechanism are barely known except for some extracellular products (ECPs), which are implicated to be regulated by quorum sensing system. In the present study, microarray was used to analyze the transcription profiles of V. alginolyticus wild-type and a deletion mutant of luxO, the pivotal regulator in Vibrio quorum sensing systems, and a putative virulence factor MviN was identified. Quantitative real-time reverse transcription PCR confirmed that the transcription of mviN was up-regulated in the luxO mutant compared to wild-type and down-regulated in the luxO-con complemented strain. Furthermore, western blotting indicated that MviN was greatly induced in the late-exponential and stationary phases of growth, demonstrating the expression of MviN was cell-density dependent and quorum sensing regulated in V. alginolyticus. The mviN null mutant displayed a much slower growth rate than wild-type, suggesting its essential role in V. alginolyticus. Western blotting also revealed that MviN was present as an extracellular protein in V. alginolyticus. When the ECPs of the mviN mutant were subjected to treat EPC cells, no cytotoxicity was observed while pathological changes of EPC cells treated by the wild-type increased with the ECPs concentration and treating time. These data showed that MviN was a LuxO-regulated component in ECPs and involved in the pathogenicity of V. alginolyticus.