Biological nitrogen fixation (BNF) is an essential source of new nitrogen for terrestrial ecosystems. The abiotic factors regulating BNF have been extensively studied in various ecosystems and laboratory settings. Despite this, our understanding of the impact of neighbouring bacteria on N2 fixer activity remains limited. Here, we explored this question using a coculture of the free-living diazotroph Azotobacter vinelandii and the non-fixing plant growth-promoting rhizobacteria Bacillus subtilis. We assessed the interaction between the two bacteria under low N availability.