rīˈzōbēəm noun
Etymology: New Latin, from rhiz- + -bium
1. capitalized : the genus of Rhizobiaceae comprising small heterotrophic soil bacteria capable of forming symbiotic nodules on the roots of leguminous plants and of there becoming bacteroids that fix atmospheric nitrogen
2. plural rhizo·bia -ēə often capitalized : any bacterium of the genus Rhizobium