Like for animals, the plant microbiota has a key role on the tree health in participating, for instance, to their growth or their protection against pathogens. Generally, the more a microbiota is diverse, the more efficient it is for its host. Some results suggest that an organisation level of this diversity could be the bacterial population that is composed of interacting sister strains with different capabilities. These variable functions, linked to the genetic diversification of the population, could enable a share of labour and create synergic actions in the niche. In return, the root exudates could affect the microbiota in increasing the frequency of gene transfer and consequently the emergence of new functions within the population. To compare the influence and the efficiency of Streptomyces populations (that belong to root microbiota) in comparison with single isolates for functions in link with the health and the growth of plants. To measure the rhizosphere effect on gene transfer events and their consequences on the diversification of a Streptomyces population. Natural Streptomyces populations are already available. They will be tested in interaction with root systems or in devices mimicking the rhizosphere for the direct or indirect growth of model plants (root development, mineral solubilisation, pathogen inhibition) and the transfer of mobile genetic elements. This project will bring a better comprehension of the ecological functioning of the root microbiota. Firstly, it will enable to define the synergic role of the bacterial population in plant-bacteria interactions and notably for the plant health. Secondly, it will enable to assess the rhizosphere influence on its microbiota and its role on the functional diversification of bacteria. Key words: Microbial population, whole genome comparison, gene transfer, plant response