We aim to elucidate bacterial mechanisms underlying symbiosis with legumes. We presently focus on two questions i) how rhizobia drive legume infection? ii) how bacterial genomes adapt to symbiosis? We work on two different experimental models, Sinorhizobium meliloti and Cupriavidus taiwanensis, for each offers specific advantages. S. meliloti, together with its host plant Medicago, is a highly evolved model symbiosis studied worldwide. C. taiwanensis, a b-proteobacterium, is representative of the rhizobial extreme diversity and together with its host plant Mimosa pudica is being used as a model of a recently evolved symbiosis. Our approaches range from molecular genetics and genomics to experimental evolution.