Intracellular translocation and localization of Edwardsiella tarda type III secretion system effector EseG in host cells

- This study illuminates the intracellular translocation and localization features of Edwardsiella tarda T3SS effector EseG.
- EseG is an internalization-depending translocation in host cells.
- EseG is specially targeted to ECV after injected to host cells.

Edwardsiella tarda, an important fish pathogenic bacterium, could utilize type III secretion system (T3SS) to transfer multiple effector proteins into host cells during infection. EseG was identified to be an E. tarda T3SS effector, which could be injected by T3SS into non-phagocytic cells. Since E. tarda is a facultative intracellular pathogen that resides and replicates in macrophage, it is interesting to expand our knowledge about EseG translocation and localization within phagocytic cells. Here utilizing murine macrophage cell line J774A.1 as the cell model, we demonstrated that EseG could be transported into J774A.1 via T3SS only after E. tarda was internalized into macrophage cells, indicating that extracellular E. tarda could not inject EseG into host cells. Subcellular fractionation analysis gave the evidence that EseG was specifically localized in the membrane fraction of infected host cells. Furthermore, immunofluorescence detection indicated that EseG specifically targeted the E. tarda-containing vacuoles (ECVs) within macrophage cells. Finally the unique features for EseG were also confirmed in non-phagocytic cells. In summarize, this work illuminates internalization-depending translocation and ECV-targeting localization of E. tarda T3SS effector in both non-phagocytic and phagocytic cells, which might be important to interpret the interaction of EseG with host cells upon infection.