Imaging type-III secretion reveals dynamics and spatial segregation of Salmonella effectors

The type-III secretion system (T3SS) enables gram-negative bacteria to inject effector proteins into eukaryotic host cells. Upon entry, T3SS effectors work cooperatively to reprogram host cells, enabling bacterial survival. Progress in understanding when and where effectors localize in host cells has been hindered by a dearth of tools to study these proteins in the native cellular environment. We report a method to label and track T3SS effectors during infection using a split-GFP system. We demonstrate this technique by labeling three effectors from Salmonella enterica (PipB2, SteA and SteC) and characterizing their localization in host cells. PipB2 displayed highly dynamic behavior on tubules emanating from the Salmonella-containing vacuole labeled with both endo- and exocytic markers. SteA was preferentially enriched on tubules localizing with Golgi markers. This segregation suggests that effector targeting and localization may have a functional role during infection.