Temperature-dependent protease LasB from Aeromonas hydrophila PS-1 mediates enteritis and pyroptosis in Pelodiscus sinensis.

Temperature is crucial for the interaction between pathogens and hosts, especially for ectotherms, which is closely related to the occurrence of disease. Chinese soft-shelled turtle ( Pelodiscus sinensis, P. sinensis), as an economically valuable aquatic species, is also an ectothermic animal. Its aquaculture industry is severely affected by pathogens. Therein, Aeromonas hydrophila ( A. hydrophila) is one of the main pathogens causing bacterial diseases in P. sinensis. Here, we found that temperature is essential for the pathogenicity of A. hydrophila to P. sinensis. What's more, a temperature-dependent virulence factor LasB, which mediated pyroptosis of intestinal fibroblast-like cells of P. sinensis was identified. Through expression detection at different temperatures, it was found that the expression level of LasB was highest at 35℃. Moreover, after knockout of lasB, the toxicity of the bacteria to intestinal fibroblast-like cells of P. sinensis was decreased, with reduced cell damage and lower LDH release rate associated with pyroptosis. Transcriptomic analysis revealed that LasB knockout significantly attenuated the upregulation of pyroptosis-related genes ( GSDMA, NLRP3, IL-1β, and IL-18) and inflammatory pathways in infected cells. After knockout of lasB, the pathogenicity of A. hydrophila to P. sinensis is significantly reduced, especially at 35℃. These results indicated that LasB played an important role in the pathogenicity of A. hydrophila, and its virulence is closely related to temperature.