Competition and selective pressures within soil microbiomes can influence a variety of mechanisms seen in rhizobia, a nitrogen-fixing bacteria that is beneficial for plant growth. Currently, rhizobia inoculants are used as a more sustainable alternative to chemical nitrogen fertilizers, which are harmful to the environment and can decrease the natural ability of rhizobia to fix nitrogen to crops. However, rhizobia inoculants compete with native rhizobia, preventing beneficial nitrogen fixation. One way we may be able to give inoculated rhizobia a competitive advantage in the microbiome is by using lysogenic bacteriophages, viruses that infect rhizobia, to induce exopolysaccharide (EPS) secretion as a defence mechanism to prevent phage infection. EPS is a main component of biofilms, which helps the rhizobia protect themselves from stressors such as competition for resources and drought. My project explores phage-rhizobia interactions and whether biofilm formation results from pre-existing plasticity or novel genetic mutations. The goal is to harness bacteriophages as selective agents to enhance EPS-producing rhizobia, improving the ability of inoculated rhizobia to outcompete native strains, enhance nitrogen fixation, and support plant growth.