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 within 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. The breadth of this technique is demonstrated by labeling three effectors from Salmonella (PipB2, SteA, and SteC) and characterizing their localizations within host cells. PipB2 displays highly dynamic behavior on tubules emanating from the Salmonella containing vacuole labeled with both endo- and exocytic markers. SteA is preferentially enriched on tubules localizing with Golgi markers. This segregation suggests effector targeting and localization may play a functional role during infection.