Vibrio parahaemolyticus CadC regulates acid tolerance response to enhance bacterial motility and cytotoxicity.

Pathogens adapted to sub-lethal acidic conditions could increase the virulence and survival ability under lethal conditions. In the aquaculture industry, feed acidifiers have been used to increase the growth of aquatic animals. However, there is limited study on the effects of acidic condition on the virulence and survival of pathogens in aquaculture. In this study, we investigated the survival ability of Vibrio parahaemolyticus at lethal acidic pH (4.0) after adapted the bacteria to sub-lethal acidic pH (5.5) for 1 hr. Our results indicated that the adapted strain increased the survival ability at lethal acidic pH invoked by an inorganic (HCl) or organic (citric) acid. RNA-sequencing (RNA-seq) results revealed that 321 genes were differentially expressed at the sub-lethal acidic pH including cadC, cadBA and groES/groEL relating to acid tolerance response (ATR), as well as genes relating to outer membrane, heat-shock proteins, phosphotransferase system and flagella system. Quantitative real-time polymerase chain reaction (qRT-PCR) confirmed that cadC and cadBA were upregulated under sub-lethal acidic conditions. The CadC protein could directly regulate the expression of cadBA to modulate the ATR in V. parahaemolyticus. RNA-seq data also indicated that 113 genes in the CadC-dependent way and 208 genes in the CadC-independent way were differentially expressed, which were related to the regulation of ATR. Finally, the motility and cytotoxicity of the sub-lethal acidic adapted wild type (WT) were significantly increased compared with the unadapted strain. Our results demonstrated that the dietary acidifiers may increase the virulence and survival of V. parahaemolyticus in aquaculture.