Nitrogen-fixing bacteria are those that directly convert atmospheric nitrogen into nitrogenous compounds. These bacteria, such as Rhizobium and Azotobacter, establish symbiotic relationships with the roots of certain plants like legumes, enabling them to fix nitrogen from the air into a usable form like ammonia. This process is vital for plant growth and agricultural productivity, as it provides an essential nutrient for plant development. In addition to symbiotic nitrogen-fixing bacteria, there are also free-living nitrogen-fixing bacteria found in soil and water that contribute to the nitrogen cycle. These bacteria play a critical role in maintaining soil fertility and supporting ecosystems. Their ability to convert nitrogen into compounds that can be assimilated by plants helps sustain food chains and biodiversity. Nitrogen-fixing bacteria are an important part of sustainable agriculture and environmental health.