The root nodules of leguminous plants houses nitrogen-fixing bacteria called Rhizobia. Rhizobia has a symbiotic relationship with leguminous plants that allows both to benefit from each other.
By binding to hydrogen, the Rhizobia bacterium is able to convert or fix nitrogen gas into ammonia , a form that the plant can use. Likewise, the legume plant provides the rhizobia bacterium with carbohydrate which the rhizobia depends on for energy. It is important to note that the carbohydrate sent to the nodules for the rhizobia is also what is used as a source of hydrogen to help the bacterium convert nitrogen to ammonia.
Enzymes are sometimes called biological catalysts