1. Nitrogen Fixation: Certain bacteria, called nitrogen-fixing bacteria, have the unique ability to convert atmospheric nitrogen (N2) into ammonia (NH3). This process is essential because atmospheric nitrogen is unavailable to most organisms. These bacteria typically live in the soil or in symbiotic relationships with plants (e.g., legumes).

2. Nitrification: Other bacteria, called nitrifying bacteria, oxidize ammonia (NH3) into nitrite (NO2-) and then into nitrate (NO3-), which is a form of nitrogen readily usable by plants. This process is called nitrification and occurs in two steps.

These two functions are crucial for the flow of nitrogen through the ecosystem and ensure that plants and other organisms have access to this essential element.