Chemical genetics discloses the importance of heme and glucose metabolism in Chlamydia trachomatis pathogenesis

• Main Author: Engström, Patrik
• Format: Doctoral Thesis
• Language: English
• Published: Umeå universitet, Institutionen för molekylärbiologi (Teknisk-naturvetenskaplig fakultet) 2013
• Subjects: Chlamydiae; heme metabolism; glucose metabolism; glucose-6-phosphate; RB-to-EB transition
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-70304; http://nbn-resolving.de/urn:isbn:978-91-7459-673-1 (printed); http://nbn-resolving.de/urn:isbn:978-91-7459-674-8 (digital)

Chlamydiae are important human bacterial pathogens with an intracellular life cycle that consists of two distinct bacterial forms, an infectious form (EB) that infects the eukaryotic host cell, and a non-infectious form (RB) that allows intracellular proliferation. To be successful, chlamydiae need to alternate between EB and RB to generate infectious EB’s which are competent to infect new host cells. Chemical genetics is an attractive approach to study bacterial pathogenesis; in principal this approach relies on an inhibitory compound that specifically inhibits a protein of interest. An obstacle in using this approach is target identification, however whole genome sequencing (WGS) of spontaneous mutants resistant to novel inhibitory compounds has significantly extended the utility of chemical genetic approaches by allowing the identification of their target proteins and/or biological pathways. In this thesis, a chemical genetics approach is used, I have found that heme and glucose metabolism of C. trachomatis is specifically important for the transition from the RB form to the infectious EB form. Heme and glucose metabolism are both coupled to energy metabolism, which suggests a common link between the RB-to-EB transitions. In connection with the above findings I have developed strategies that enable the isolation of isogenic C. trachomatis mutant strains. These strategies are based on WGS of spontaneous mutant populations and subsequent genotyping of clonal strains isolated from these mutant populations. Experiments with the mutant strains suggest that the uptake of glucose-6-phosphate (G-6-P) regulates the RB-to-EB transition, representing one of the first examples where genetics has been used to study C. trachomatis pathogenesis. Additional experiments with the mutant strains indicate that G-6-P promotes bacterial growth during metabolic stress. In concert with other findings presented in this thesis, I have fine-tuned methods that could be employed to reveal how novel inhibitory chemical compounds affect chlamydiae. In a broader context, I suggest that C. trachomatis could be used as a model organism to understand how new inhibitory drugs affect other bacterial pathogens. In addition, I observed that C. pneumoniae infections resulted in generalized bone loss in mice and that these mice display a cytokine profile similar to infected bone cells in vitro. Thus, this study indicates that C. pneumoniae potentially can infect bone cells in vivo, resulting in bone loss, alternatively, the inflammatory responses seen in vivo could be the causative factor of the bone loss observed.