The role and function mechanism of tapP in modulating the virulence of Aeromonas hydrophila

Abstract

Aeromonas hydrophila (A. hydrophila) is a widespread pathogen capable of infecting most freshwater fish and causing septicemia. Type IV pili are one of the major virulence factors of A. hydrophila and play a key role in virulence and adhesion to the host. TapP is known to be involved in the synthesis of type IV pili. However, the effect and molecular mechanism of the tapP in A. hydrophila remain unknown. In this study, we constructed a genetically stable tapP deletion mutant strain of A. hydrophila (ΔtapP-AH), the median lethal dose (LD50) value of the ΔtapP-AH in Carassius auratus gibelio was 3.1-fold higher than that of the wild-type strain (WT-AH). The transmission electron microscopy (TEM) results showed that ΔtapP-AH exhibited sparser pili. The ability of adhering to gill tissues and biofilm formation was significantly reduced in ΔtapP-AH. For motility, the swimming ability of ΔtapP-AH was significantly higher, no significant difference was found in twitching and swarming abilities. We further investigated the effect of tapP gene deletion on the expression of virulence related factor genes to explore the molecular mechanisms of attenuated virulence and altered biological characteristics. The results indicated that deletion of the tapP directly affected the expression of genes related to type IV pili, type II secretion system, type VI secretion system and flagellum, but had no effect on the genes related to type I pili. In conclusion, this study provides new insights into the function of the tapP and the pathogenic mechanism in A. hydrophila.