Biological function and mechanism of flpL gene in regulating pathogenicity of Aeromonas hydrophila

Aeromonas hydrophila is human-animal commensal bacterium that seriously threatens the development of aquaculture and human health. Type IV pili (T4P) are essential for bacterial physiological function. The relationship between the molecular mechanism of flpL gene affiliated to T4P and the pathogenicity is still unclear. In the research, A. hydrophila with a genetically stable deletion of flpL gene (Δ flpL ) was constructed. The median lethal dose of Δ flpL for Crucian carp was 4.87 times higher compared to wild-type strain, suggesting that Δ flpL significantly reduced pathogenicity. The attenuation may be attributed to a reduced capacity for biofilm formation and downregulation of the expression levels of virulence-related genes in Δ flpL . Meanwhile, the significant increase in swimming capacity and adhesion can be related to the upregulation of flpC, tapM, tapB and tapP genes. In conclusion, flpL gene plays essential role in the pathogenicity, adhesion, motility, and capacity for biofilm formation in A. hydrophila . The research aims to clarify the pathogenesis of A. hydrophila , and lay the foundation for developing live attenuated vaccines through the targeted modification flpL gene.