Rhizobia

Rhizobia bacteria in nodules fix nitrogen

Soybean root nodules, each containing billions of Bradyrhizobium bacteria

Rhizobia are soil bacteria which become established inside root nodules of legumes (the pea family: Fabaceae).

They fix nitrogen in a form the plant can use. Rhizobia require a plant host; they cannot independently fix nitrogen. The relationship is a classic example of symbiosis and mutualism.

The word rhizobia comes from the English root for root (rhizo) and the Ancient Greek for life (bios).