TCS regulator CpxR of Edwardsiella piscicida is vital for envelope integrity by regulating the new target gene yccA, stress resistance, and virulence

Edwardsiella piscicida is a serious pathogen in aquaculture and has become a model strain for the study of aquatic pathogenic bacteria. The two-component system (TCS) CpxRA is known to be intimately correlated with the adversity resistance and virulence of multiple pathogens. However, the role of CpxRA remains vague in most aquatic pathogens, especially E. piscicida. In this study, by constructing an in-frame mutant strain of cpxR, we find that CpxR of E. piscicida is closely involved in bacterial resistance to high temperature, antibiotics, and osmotic stress, which is further confirmed by the finding that CpxR is essential for cell membrane integrity. Our result also illustrates that CpxR is required for bacterial resistance against host serum and biofilm formation. Subsequent pathogenicity experiments display that CpxR is indispensable for bacterial adhesin to epithelial cell and bacterial survival and replication in phagocyte, and that CpxR is essential for bacterial colonization and dissemination in host immune tissues and general virulence. The regulatory mechanism of CpxR is clarified by the result that CpxR positively regulates the transcription of yccA, which is a new target gene of CpxR. The regulation of CpxR on yccA is decisive for envelope integrity. Taken together, these findings provide compelling evidence that CpxR of E. piscicida is not only crucial for bacterial resistance against envelope stress, but also is indispensable for bacterial virulence, which is conducive to have an insight into the importance of CpxRA system in aquatic pathogens.