Which organism is responsible for helping leguminous plants in nitrogen fixation?

A symbiotic relationship is a close and long-term interaction between two or more different species living together in a mutually beneficial or dependent relationship.

Legume plants have a symbiotic relationship with nitrogen-fixing bacteria called Rhizobia. The bacteria colonize the roots of the legume plants, forming specialized structures called nodules. Inside the nodules, the bacteria convert atmospheric nitrogen into a form that the plants can use. In return, the plants provide the bacteria with carbohydrates. This relationship is known as mutualism and is essential for soil fertility.

Pathogens, cocci, and anaerobes do not have a role in nitrogen fixation in leguminous plants.