What role do nitrogen-fixing bacteria play in the nitrogen cycle?

Nitrogen-fixing bacteria play a crucial role in the nitrogen cycle by converting atmospheric nitrogen (N₂) into ammonia (NH₃) through a process called nitrogen fixation. This transformation is essential because atmospheric nitrogen is not usable by most living organisms. Instead, plants and other organisms need nitrogen in a reactive form, such as ammonia or nitrate, to synthesize proteins and other important biological molecules.

The process begins when these bacteria, which can be free-living in the soil or symbiotic with the roots of certain plants (like legumes), take in atmospheric nitrogen and, through complex biochemical reactions, convert it into ammonia. This ammonia can then be used by plants as a nutrient, either directly or after being further processed into other forms, like nitrites or nitrates, by different bacteria in the soil.

This function of nitrogen-fixing bacteria is fundamental for maintaining soil fertility and supporting the growth of plants, thus playing a vital role in ecosystems and agricultural productivity.