Deciphering the genetic and epigenetic mechanisms of bacterial adaptation to lifestyle changes along the pathogenicity-mutualism continuum – LIFEPATH

Along with the evolution of animals and plants, bacteria have evolved the capacity to interact intimately with eukaryotic cells. These associations form a dynamic continuum from pathogenicity to mutualism along which bacteria can rapidly evolve and change their lifestyle. However, the molecular mechanisms by which bacteria adapt to new hosts and new types of interaction are poorly known. In this project, we propose to jointly analyze a unique combination of two evolution experiments, in which the same plant pathogenic soil bacterium, Ralstonia solanacearum, was adapted to different hosts on one hand and to a different lifestyle, endosymbiosis with a legume, on the other hand. The molecular bases underlying (1) the propensity of this pathogen to have a very broad host range and recurrently emerge on novel hosts and (2) the emergence of phylogenetically diverse nitrogen-fixing legume symbionts will be elucidated. Both the mode (genetic and epigenetic with a special focus on methylome modifications) and the molecular targets (biological functions) of these adaptive processes will be analyzed. Commonalities but also specificities leading to the different lifestyles will be highlighted. Finally, pre-requisite functions necessary for the colonisation of specific hosts or predisposing to symbiosis with legumes will be identified. Thus, the project will shed light on the adaptive mechanisms involved in evolutionary transitions in bacteria, phenomena of critical importance in a context of global change, where human activities are transforming terrestrial biomes at unprecedented rates.