Bacteria play a crucial role in the nitrogen cycle by converting atmospheric nitrogen into forms usable by plants and other organisms. This process begins with nitrogen-fixing bacteria, which convert nitrogen gas (N₂) into ammonia (NH₃) during nitrogen fixation. Subsequently, nitrifying bacteria transform ammonia into nitrites (NO₂) and then into nitrates (NO₃), which plants can absorb as nutrients. Lastly, denitrifying bacteria convert nitrates back into nitrogen gas, completing the cycle. This cycle is vital for soil fertility and ecosystem health, as it ensures a continuous supply of nitrogen, an essential nutrient for all living beings.