Abstract
Chlamydia spp. utilize multiple secretion systems, including the type III secretion system (T3SS), to deploy host-interactive effector proteins into infected host cells. Elucidation of secreted proteins has traditionally required ectopic expression in a surrogate T3SS followed by immunolocalization of endogenous candidate effectors to confirm secretion by chlamydiae. The ability to transform Chlamydia and achieve stable expression of recombinant gene products has enabled a more direct assessment of secretion. We adapted TEM-1 β-lactamase as a reporter system for assessment of chlamydial protein secretion. We provide evidence that this system facilitates visualization of secretion in the context of infection. Specifically, our findings provide definitive evidence that C. trachomatis CT695 is secreted during infection. Follow-up indirect immunofluorescence studies confirmed CT695 secretion and indicate that this effector can be secreted at multiple points during the chlamydial developmental cycle. Our results indicate that the BlaM-fusion reporter assay will allow efficacious identification of novel secreted proteins. Moreover, this approach can easily be adapted to enable more sophisticated studies of the secretion process in Chlamydia.
Highlights
Chlamydia trachomatis are agents of human sexually transmitted disease, whereas ocular infections with C. trachomatis serovars A-C can lead to blindness [1]
We provide proof-of-principle evidence that this system allows the robust detection of T3SE secretion in a tissue-culture infection model
We reveal for the first time that C. trachomatis CT695 is secreted by chlamydiae at multiple stages of the developmental cycle
Summary
Chlamydia trachomatis (serovars D-K and lymphogranuloma venereum serovars L1-L3) are agents of human sexually transmitted disease, whereas ocular infections with C. trachomatis serovars A-C can lead to blindness [1]. Development is initiated when infectious particles termed elementary bodies (EBs) invade host cells and differentiate into. Chlamydia Secretion Reporter System noninfectious, vegetative forms termed reticulate bodies (RBs). RB growth is eventually accompanied by asynchronous conversion of RBs to EBs. Subsequent exit from the host cell is mediated by lysis or extrusion [4]. Intracellular development occurs entirely within a parasitophorous vacuole termed an inclusion. Chlamydiae develop effectively segregated from the host cytosol since the inclusion membrane is passively impermeable to molecules >520 Da [5]. Despite this physical separation, Chlamydia spp. are capable of directly modulating host cell biology. Members of the Chlamydiaceae all express a type III secretion system (T3SS) to promote survival from within a protected niche
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