Rhizobia are soil bacteria belong to genus of gram-negative, rod shaped, aerobic and motile bacteria. They are known for their ability to establish a symbiotic relationship with leguminous plants. There are different types of genera, such as Azorhizobium, Bradyrhizobium and Sinorhizobium together with Rhizobium, collectively known as rhizobia. Members of the genus Rhizobium specifically form root nodules, but some rhizobia have ability to form nodules on plant stems such as Azorhizobium caulinodans form stem nodules on sesbania plants.