Intracellular growth of Chlamydia trachomatis leads to global histone hypermethylation by impairing demethylation.

Chlamydia trachomatis, an intracellular bacterium, highjacks metabolites from the host cell for its own proliferation. We provide evidence of global hypermethylation of the host proteome, including histones, during the late stages of infection. Single cell analyses revealed co-occurrence of several methylated residues on histones, while infection did not alter S-adenosyl methionine levels. Histone hypermethylation correlated positively with bacterial load and was prevented by antibiotic treatment. Mapping of trimethylation of histone 3 at residues K4 and K9 revealed a broad distribution throughout chromatin. Nuclear fractions of infected cells exhibited a fourfold decrease of demethylase activity against H3K4me3 and a twofold increase in succinate concentration, a competitive inhibitor for the demethylase co-factor a-ketoglutarate. Supplementation of the culture medium with dimethyl-ketoglutarate (DMKG) or with iron, a second co-factor of histone lysine demethylases, reduced histone hypermethylation. DMKG supplementation modified the transcription of about one third of the infection-responsive genes, indicating that histone hypermethylation contributes to modulating the transcriptional response of the host to infection. Finally, chemical inhibition of histone demethylases in a mouse model of infection showed a moderate benefit regarding the outcome of infection. Overall, our data show that the metabolic pressure exerted by a pathogen with an intracellular lifestyle drives epigenetic changes in infected cells.