Effect of tryptophan starvation on inclusion membrane composition and chlamydial-host interactions.

Chlamydia is an obligate intracellular bacterial pathogen that develops within a membrane-bound vacuole called an inclusion. Throughout its developmental cycle, Chlamydia modifies the inclusion membrane (IM) with type III secreted (T3S) membrane proteins, known as inclusion membrane proteins (Incs). Via the IM, Chlamydia manipulates the host cell to acquire lipids and nutrients necessary for its growth. One key nutrient is tryptophan (Trp). As a Trp auxotroph, Chlamydia is very sensitive to Trp starvation and, in response to low Trp levels induced by the immune response, enters a viable but nonreplicating state called persistence. To maintain viability during persistence, Chlamydia must necessarily maintain both the integrity of the IM and its ability to modify host cell responses, but how Trp starvation affects IM composition and subsequent interactions with the host cell remains poorly understood. We hypothesize that, under Trp starvation conditions, Inc expression/stability or T3S function during persistence alters IM composition but that key host-Chlamydia interactions will be preserved. To examine host-Chlamydia interactions during persistence, we examined sphingomyelin, cholesterol, and transferrin trafficking to the inclusion, as well as localization of host proteins that bind to specific Incs. We identified IM composition changes during persistence by monitoring endogenous Inc abundance at the IM. Chlamydial T3S is generally functional during persistence. Specific changes in Inc composition in the IM can be linked to Trp content of a specific Inc or effector-specific defects in chlamydial T3S. Overall, our findings reveal that critical host-Chlamydia interactions are maintained during persistence mediated by Trp starvation.