rhizobium
noun
rhi·zo·bi·um rī-ˈzō-bē-əm 
plural rhizobia rī-ˈzō-bē-ə
: any of a genus (Rhizobium) of small heterotrophic soil bacteria capable of forming symbiotic nodules on the roots of leguminous plants and of there becoming bacteroids that fix atmospheric nitrogen
rhizobial
rī-ˈzō-bē-əl
adjective 
Word History
Etymology
New Latin, from rhiz- + Greek bios life — more at quick entry 1
First Known Use
1890, in the meaning defined above
Medical Definition
rhizobium
noun
rhi·zo·bi·um rī-ˈzō-bē-əm
1
capitalized : a genus (family Rhizobiaceae) of small heterotrophic soil bacteria capable of forming symbiotic nodules on the roots of leguminous plants where they fix atmospheric nitrogen
2
plural rhizobia -bē-ə : any bacterium of the genus Rhizobium
: any bacterium of the genus Rhizobium