Contribution of the type IV pili secretin tapQ to motility, growth, adhesion, stress tolerance and virulence of Aeromonas hydrophila.

Aeromonas hydrophila (A. hydrophila) is a widely distributed opportunistic aquatic pathogen. Type IV pili (T4P) are regarded as key virulence factors of A. hydrophila that play a pivotal role in virulence, and tapQ is a component of T4P. However, the role and mechanism of tapQ in the pathogenicity of A. hydrophila are not clear. In this study, a stable genetically tapQ mutant strain of A. hydrophila (ΔtapQ-AH) was constructed. The median lethal dose value of ΔtapQ-AH in Carassius auratus was 0.82-fold that of wild-type strain of A. hydrophila (WT-AH), indicating that ΔtapQ-AH packs a stronger dose of virulence. The ΔtapQ-AH exhibited a significant increase in swimming, biofilm formation, adhesion, osmotic and oxidative stress resistance abilities compared with WT-AH. Twitching and growth abilities showed significant reductions. Exploring the molecular mechanism of the effect of tapQ gene deletion on virulence and biological properties, we found that tapQ gene mutation would affect gene expression of the phage shock protein (Psp) system, type II secretion system, flagellum, type IV pili, type VI secretion system and outer membrane protein. Taken together, this study initially reveals the role of the tapQ gene and offers novel insights into the mechanisms of virulence regulation in A. hydrophila.