Dissection Of Twin Arginine Translocation System And Type Six Secretion System In V. Alginolyticus

In the long evolution, bacteria are adapted to use differnt kinds of protein translocation system to survive and colonize various niches. As two secretion systems totally different from traditonal gerneral secretion pathway (GSP), twin arginine translocation system (Tat) and type six secretion system (T6SS), play important roles in the ability to adapt to various environmental stresses and in bacterial pathogenesis.Vibrio alginolyticus has been reported to be one of the dominant causative agents of high-mortality outbreaks of vibirosis in mariculture of South China. The virulent determinants of this specie have not been well characterized yet. The viruluent genes such as tlh, trh, toxR, ctxA and VPI show no direct relationship with the virulence of V. alginolyticus. The previous study in our lab indicated that the alkaline serine protease (Asp) was closely associated with the virulent mechanism of V. alginolyticus, and its expression was strictly regulated by quorum sensing system in the bacterium. In order to investigate the putative secretion mechanism of Asp, this work focused on the Tat system and T6SS in V. alginolyticus and analysed the relationship between there two different kinds of secretion systems and the virulence mechanism of V. alginolyticus.In this study we identified the Tat gene cluster in fish pathogen V. alginolyticus and explored its roles in stress adaptation and pathogenesis toward fish. At the meantime, two T6SS gene clusters were also identified. Gene analysis revealed that Tat locus in V. alginolyticus shares high similarity with that from E. coli and V. cholerae. In V. alginolyticus, deletion of the tat ABC genes led to a drastic decrease in biofilm biogenesis, swarming ability and the viability under various stresses such as oxidation, temperature shift, ethanol treatment, osmotic challenge and iron limitations. Interestingly, significantly decreased secretion of the extracellular Asp, an established exotoxin of the bacterium, was observed in the TatC mutant, suggesting that TatC might play a role in the production of virulence factors in the bacterium. Furthermore, the Tat mutants displayed attenuated virulence towards the fish model. The T6SS mustants showed sharp decrease in the production of Asp and also displayed attenuated virulence towards the fish. The findings that Tat secretion and T6SS related to the extracellular Asp as well as virulence in V. alginolyticus provided new insights into the pathogenesis of vibirosis in fish.