Rhizobia are a group of bacteria that play a crucial role in the nitrogen cycle. They are known for their ability to form symbiotic relationships with the roots of leguminous plants, such as soybeans and clover. In this partnership, rhizobia convert atmospheric nitrogen into a form that plants can use for growth, enhancing soil fertility. These bacteria live in nodules on the roots of their host plants, where they provide essential nutrients in exchange for carbohydrates produced by the plants through photosynthesis. This mutualistic relationship not only benefits the plants but also contributes to sustainable agriculture by reducing the need for chemical fertilizers.