How plants deal with beneficial and pathogenic microorganisms and how they can tolerate beneficial ones and face to pathogens in the same time are questions that remain puzzling to plant biologists. Legume plants are good models to explore those issues as their interactions with nitrogen-fixing bacteria, rhizobia, results in a drastic and easy to follow phenotype of nodulation. Intriguingly, despite massive and chronic infection, legumes defense reactions are essentially suppressed during the whole symbiotic process rising the question about a potential negative effect of plant immune responses on the establishment of nodulation. In the present study, we used the model legume, Medicago truncatula, co-inoculated with a mutualistic and with a phytopathogenic bacteria, Sinorhizobium medicae and Ralstonia solanacerarum. We show that the presence of R. solanacearum drastically inhibits the nodulation process. The type three secretion system (TTSE) of R. solanacearum, that is important for the inhibition of PAMP (Pathogen Associated Molecular Patterns) triggered immunity (PTI), strongly contributes to inhibit nodulation. Thus, our results question the negative effect of PTI on nodulation. By including a pathogenic bacterium in the interaction system, our study provides a new angle to address the influence of the biotic environment on the nodulation process.