Rhizobium belong to sub group of bacteria called:

Explanation

Proteobacteria is a phylum of gram-negative bacteria. The Proteobacteria are further divided into 5 classes: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, and Epsilonproteobacteria.The first class of Proteobacteria is the Alphaproteobacteria, many of which are obligate or facultative intracellular bacteria. Some species are characterized as oligotrophs, organisms capable of living in low-nutrient environments such as deep oceanic sediments. Rhizobium is a genus of alphaproteobacteria. Rhizobium are gram-negative nitrogen-fixing bacteria that occur either as free-living soil bacteria or in interaction with the roots of leguminous plants.