A conserved Chlamydiota-specific Type III Secretion System effector linked to stress response

Area of Science:

• Microbiology
• Bacterial stress response
• Chlamydial pathogenesis

Background:

• Members of the Chlamydiota phylum exhibit a conserved stress response involving aberrant body formation.
• The molecular mechanisms underlying this stress response, particularly upon exposure to diverse stressors, remain largely uncharacterized.
• Wcw_0502, a type III secretion system (T3SS) effector in Waddlia chondrophila, is upregulated during iron starvation-induced aberrant body formation.

Purpose of the Study:

• To investigate the regulation of the wcw_0502 gene and its homologues in response to various stressors in Chlamydiota.
• To elucidate the role of the HrcA repressor and Hsp60 chaperone in controlling wcw_0502 transcription.
• To characterize the structural features and potential functions of the Wcw_0502 effector protein.

Main Methods:

• Quantitative reverse transcription PCR (qRT-PCR) to measure wcw_0502 and ctl0271 RNA levels under different stress conditions (iron starvation, heat shock).
• Chromatin immunoprecipitation (ChIP) assays to assess the binding of HrcA and Hsp60 to the promoter regions of wcw_0502 and its homologues.
• Bioinformatic analysis to identify conserved regulatory elements and protein domains.

Main Results:

• Iron starvation induced significant upregulation of wcw_0502 in *Waddlia chondrophila* aberrant bodies.
• This upregulation of *wcw_0502* upon iron starvation was not conserved in other chlamydial species, including *Chlamydia trachomatis* and *Chlamydia pneumoniae*.
• Heat shock was the only stressor that strongly upregulated both *wcw_0502* and its *C. trachomatis* homologue, *ctl0271*.
• A conserved Controlling Inverted Repeat of Chaperone Expression (CIRCE) element was identified in the promoter regions, suggesting HrcA/Hsp60-mediated repression.
• Decreased occupancy of HrcA and Hsp60 at the *wcw_0502* promoter was observed in iron starvation-induced aberrant bodies, correlating with gene upregulation.
• Wcw_0502 possesses a novel cystine knot-like domain, known for its resistance to proteolytic, chemical, and thermal degradation.

Conclusions:

• The regulation of the *wcw_0502* gene is stress- and species-specific within the Chlamydiota phylum.
• The HrcA/Hsp60 repressor complex likely controls *wcw_0502* transcription via the CIRCE element, with stress-induced dissociation leading to upregulation.
• The unique cystine knot-like domain suggests Wcw_0502 plays a role in protecting bacterial components or facilitating host-pathogen interactions under stress conditions.