Is Rhizobium gram-positive or negative?

Rhizobium is a gram-negative organism:

1. Rhizobium is a gram-negative motile rod-shaped proteobacterium.
2. It can live freely in the soil or can be in symbiotic association with legumes.
3. Infection of the roots of a legume with Rhizobium leads to root nodule formation.
4. Rhicadhesin, a calcium-binding protein that is present on the surface of Rhizobium species helps in the attachment of the legumes to the Rhizobium species.
5. Root exudates play an important role in nodule formation as they induce nod genes which are responsible for nodule formation.