1. Cyanobacteria: These are photosynthetic bacteria found in various environments, including aquatic ecosystems and soils. They have a specialized enzyme called nitrogenase that allows them to convert atmospheric nitrogen (N2) into ammonia (NH3).
2. Certain bacteria living in the roots of legumes: Legumes (plants like peas, beans, and lentils) have a symbiotic relationship with nitrogen-fixing bacteria called rhizobia. These bacteria reside in nodules on the plant roots and convert atmospheric nitrogen into a form usable by the plant.
While other sources of nitrogen fixation exist (like industrial processes and some other bacteria), these two are responsible for the vast majority of the nitrogen made available to living organisms on Earth.
