Manipulation des nucléotides par la bactérie intracellulaire obligatoire Chlamydia trachomatis

Chlamydia trachomatis is an obligate intracellular bacterium that infects human epithelial cells of the urogenital tract. This pathogen is known as the most common sexually transmitted infection. Certain strains can also infect the ocular conjunctiva, which can develop into trachoma, the leading cause of bacterial blindness.The intracellular development of the bacterium in a membrane compartment, called an inclusion, within the cell cytoplasm has made C. trachomatis dependent on the host for the acquisition of nucleoside triphosphates (NTP), the building blocks of RNA and DNA (in the form of deoxynucleotides, dNTP). As membranes are not permeable to nucleotides, these metabolites, or their precursors, are transported by specific transporters. Only bacterial NTP transporters, Npt1 and Npt2, have been identified to import NTP from the inclusion into bacteria, raising the question of how host nucleotides become accessible in the inclusion.This thesis focuses on two main aspects: firstly, the strategies implemented by C. trachomatis to access host nucleotides, and secondly, the characterization of the bacterial protein CtMazG, which exhibits a hypothetical nucleotide pyrophosphohydrolase function. In the host cell, nucleotides are synthesized by two pathways: the salvage pathway, which synthesizes nucleotides (phosphorylated forms of nucleosides) from imported nucleosides, and the de novo pathway, where nucleotides are synthesized from other cellular metabolites. Our data demonstrate that both nucleotide synthesis pathways contribute to the supply of C. trachomatis. In addition, we show that nucleotides, not nucleosides, are imported into the inclusion. However, our efforts to identify the transporters responsible for this import were unsuccessful.In parallel, we explored the role of the bacterial protein CtMazG in C. trachomatis infection. We confirmed the nucleotide pyrophosphohydrolase activity, particularly for purine dNTPs (dATP and dGTP), leading to the generation of monophosphate forms of purine deoxynucleosides. Our data show that CtMazG is necessary for optimal bacterial development, and that its absence results in the accumulation of mutations. In many other organisms, MazG's role in genome preservation is linked to its specialization in oxidized nucleotides, but this is not the case for CtMazG. Instead, our data suggest that CtMazG balances the relative levels of dNTP, thereby contributing to the fidelity of the genome replication step. CtMazG also plays an important role in the entry of bacteria into their proliferative phase, again possibly by balancing dNTP.In conclusion, this project has enabled us to gain a better understanding of the strategies employed by C. trachomatis to access host nucleotides, and to elucidate the role of a bacterial enzyme modulating dNTP in the development of C. trachomatis.