The roles of the BarA-UvrY two-component system in the virulence of Vibrio harveyi and the efficacy evaluation of mutant strains ΔbarA and ΔuvrY as live-attenuated vaccines.

Abstract

As key bacterial signaling mechanisms, two-component systems (TCSs) regulate numerous cellular processes, with the BarA/UvrY system particularly important for controlling stress adaptation and virulence. However, the functions of BarA/UvrY in Vibrio harveyi, a major vibriosis-causing pathogen in marine fish, are still unclear. In this study, we analyzed the V. harveyi typical phenotypic alterations following barA and uvrY deletion, and the result indicated that deletion of barA and uvrY decreased maximum growth density and motility, and increased the susceptibility to pH stress, iron limitation, and antibiotics in V. harveyi. Besides, the biofilm formation pattern is a time-dependent process in V. harveyi. In addition, deletion of barA and uvrY reduced bacterial adhesion, intracellular ferrous ion concentration, while also increasing apoptosis and viability in host cell. Furthermore, the mutation impaired the ability of the bacteria to invade and replicate within primary grouper macrophages. Lastly, immunization with ΔbarA and ΔuvrY stimulated host immune responses through upregulation of immune-related genes and increased serum enzyme activity, providing substantial protection against V. harveyi infection in grouper. These results provide crucial insights into BarA/UvrY regulatory system of γ-proteobacteria and reveal novel aspects of pathogenic strategies employed in marine fish hosts.