Identify the nitrogen-fixing bacteria present in root nodules of leguminous plants.

Leguminous plants like pea have nitrogen-fixing bacteria called Rhizobium in their root nodules. Rhizobium helps in converting atmospheric nitrogen into ammonia that can be utilized by the pea plant for its nutrition. Other bacteria like Nitrosomonas and Azotobacter are free-living soil bacteria that also help in nitrogen fixation.