AcsS inhibits the hemolytic activity and thermostable direct hemolysin (TDH) gene expression in Vibrio parahaemolyticus

Vibrio parahaemolyticus produces a key virulent factor known as thermostable direct hemolysin (TDH). TDH exhibits diverse biological activities, including hemolytic activity. The β-type hemolysis observed on Wagatsuma agar due to TDH is recognized as the Kanagawa phenomenon (KP). The tdh2 gene is primarily responsible for TDH production and the associated KP. AcsS was originally identified as an activator of swimming and swarming motility in V. parahaemolyticus. However, the extent of its potential to regulate other cellular pathways remains unclear. In this study, we explored the regulatory effects of AcsS on the hemolytic activity and tdh2 expression in V. parahaemolyticus. The data showed that V. parahaemolyticus hemolytic activity and tdh2 transcription were under the negative control of AcsS. Additionally, in vitro binding assays revealed that His-AcsS could not bind to the regulatory DNA region of tdh2. However, overexpression of AcsS in an Escherichia coli strain suppressed the expression of tdh2. Collectively, these results suggested that AcsS suppresses the hemolytic activity of V. parahaemolyticus through the downregulation of tdh2 transcription. The data enhanced our understanding of the regulatory networks governing tdh2 expression and the roles of AcsS in this bacterium.