What is the relationship between a bean plant and the bacteria growing in the root nodules?

Nitrogen-fixing bacteria live in the root nodules and take atmospheric nitrogen out of the air and convert it to ammonia in the soil. The ammonia is then converted into nitrates and nitrites by nitrifying bacteria in the soil for plants to use through the process of assimilation. The bacteria in the nodes have a mutualistic relationship with the bean plant because they provide it with the essential nitrites and nitrates by performing ammonification.