Défense de thèse de doctorat en sciences biologiques, par Thi Anh Phuong Ong

Growth control of Brucella abortus in human trophoblasts JEG-3 cells

Jury

Laurence VAN MELDEREN (ULB), Johann MIGNOLET (Syngulon et UCL), Suzana SALCEDO (Université de Lyon), Jean-Yves MATROULE, président (UNamur), Xavier DE BOLLE, promoteur (UNamur)

Résumé

The intracellular Brucella pathogens cause a worldwide zoonosis named Brucellosis. They are facultative intracellular pathogens, able to replicate in several cell types, including trophoblasts of pregnant hosts. In the study using HeLa cells or RAW 264.7 macrophages, Deghelt et al. (2014) showed that in these cell types B. abortus blocks its growth and its cell cycle at the G1 stage during the first hours of infection. Trophoblasts are a natural site for B. abortus proliferation since Anderson et al. (1986) described that trophoblasts of pregnant goat contain numerous B. abortus at 5 days post-inoculation. We found that in human trophoblast cell line JEG-3, a majority of B. abortus start their growth already at 2 hours post-infection (PI). We also found that G1-arrested bacteria are not the predominant infectious form of B. abortus in the infection to JEG-3 cells. This suggests that the entry of B. abortus into trophoblasts JEG-3 cells is different with HeLa cells and that trophoblasts cells provides a different growth-permissive environment compared to HeLa cells or RAW 264.7 macrophages.

A Tn-seq analysis was conducted to analyse the factors crucial for survival until 5 hours post-infection in JEG-3 cells, that were not identified in RAW 264.7 macrophages at the same time post-infection. This analysis identified two potential regulators of cell cycle, a cyclic-di-GMP diesterase named PdeA (also called BpdA) and the histidine kinase PleC. Interestingly, both pdeA and pleC mutants display a lower proportion of growing bacteria at 5 h post-infection, compared to the wild type strain, suggesting that PdeA (and thus c-di-GMP level) and PleC are involved in the control of B. abortus growth inside JEG-3 cells. In Caulobacter crescentus, PdeA and PleC are involved in the control of the level of cyclic di-GMP, a second messenger molecule, since PdeA degrades c-di-GMP in the swarmer cells (flagellated cells) (Abel et al., 2011) and PleC is required also to lower c-di-GMP concentrations in the swarmer cells (Christen et al., 2010), among other functions. We thus propose that c-di-GMP concentrations could control growth of B. abortus inside JEG-3 cells.

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