Direct visualization of the expression and localization of chlamydial effector proteins within infected host cells.

Chlamydia secrete into host cells a diverse array of effector proteins, but progress in characterizing the spatiotemporal localization of these proteins has been hindered by a paucity of genetic approaches in Chlamydia and also by the challenge of studying these proteins within the live cellular environment. We adapted a split-green fluorescent protein (GFP) system for use in Chlamydia to label chlamydial effector proteins and track their localization in host cells under native environment. The efficacy of this system was demonstrated by detecting several known Chlamydia proteins including IncA, CT005 and CT694. We further used this approach to detect two chlamydial deubiquitinases (CT867 and CT868) within live cells during the infection. CT868 localized only to the inclusion membrane at early and late developmental stages. CT867 localized to the chlamydial inclusion membrane at an early developmental stage and was concomitantly localized to the host plasma membrane at a late stage during the infection. These data suggest that chlamydial deubiquitinase play important roles for chlamydial pathogenesis by targeting proteins at both the plasma membrane and the chlamydial inclusion membrane. The split-GFP technology was demonstrated to be a robust and efficient approach to identify the secretion and cellular localization of important chlamydial virulence factors.