RESUMO
Vibrio alginolyticus has brought about severe economic damage to the mariculture industry by causing vibriosis in various fish species in South China. The virulent determinants of this bacterium have not been well characterized except the exotoxin alkaline serine protease, Asp. In addition, the mechanism of virulence regulation in V. alginolyticus remains largely unknown apart from a Vibrio harveyi-like quorum sensing (QS) system which is established to manipulate the expression of various virulence-related genes. Hfq, an sRNA chaperone, is an important post-transcriptional regulator in a variety of bacteria. Here, the roles of Hfq were characterized in regulating the stress resistance and pathogenesis in V. alginolyticus. We demonstrated that the hfq deletion mutant became more sensitive to several environmental stresses, including osmotic stress, ethanol, temperature shift, and iron starvation. The deletion of hfq abrogated the motility and biofilm formation in this bacterium. Hfq negatively regulated the expression of main virulence factor, Asp, through QS system. The results also indicated that Hfq modulated the survival and multiplication of V. alginolyticus in fish. Hfq thus appears to be a new pleiotropic regulator of pathogenesis in V. alginolyticus. Moreover, high immunoprotective rate was achieved with a single dose of injection or immersion vaccination with live hfq mutant, suggesting the mutant's merits as a valuable vaccine candidate against V. alginolyticus.
