Rising occurrences of drought in southern Europe necessitate the expansion of local soybean cultivation towards northern latitudes. The establishment of symbiosis with indigenous rhizobia strains acclimatized to these regions is crucial for efficient nitrogen fixation and the production of protein-rich beans. A recent citizen science initiative has unveiled the coexistence of beneficial local Bradyrhizobium sp. and non-diazotrophic Tardiphaga robiniae within functional soybean nodules, raising questions about their role as either symbiotic facilitators or competitive exploiters. To unravel this enigma, we will examine soybean physiological responses to co-inoculation with both bacteria, and concurrently monitor their colonization dynamics through fluorescent tagging. This approach aims to delineate the inter-bacterial competition and characterize the impact of Tardiphaga on Bradyrhizobium colonization within soybean nodules. Employing advanced molecular techniques such as bulk RNA-sequencing and spatial omics, will scrutinize the influence of Tardiphaga on soybean gene expression and metabolite production. By pinpointing key soybean genes, we will clarify the influence of Tardiphaga on the symbiosis, providing insights to refine commercial soybean inoculants and to be exploited for gene editing and marker-assisted breeding. This project holds promise for enhancing the overall efficiency and sustainability of agricultural soybean production at northern latitudes.