Rhizobium is a symbiotic (diazotrophs) Nitrogen fixer which forms nodules in specific leguminous plants and fixes atmospheric nitrogen. They provide plant with nitrogen and take food (carbon) from them. They are heterotrophs possessing a special enzyme nitrogenase this enzyme allows them to convert nitrogen gas into ammonium.
Diazotrophs- An organism which is able to grow without external sources of fixed N. All diazotrophs contains Fe-Mo nitrogenase systems.
Morphology of Rhizobium bacteria:
1.Unicellular heterotrophs.
2.Small to medium sized 0.5-0.9 X 1.2-3.0 microns.
3.Gram negative non sporulating rods.
4.They are motile when young and have peritrichous flagella.
5.Cells contain characteristic granules of polymerized beta hydroxyl butyrate (40-50 % of cell dry weight).
6.Most strains produce gum (extracellular polysaccharide slime) of varying composition.
7.A large irregularly shaped nuclear region in centre surrounded by a narrow region of denser cytoplasm.
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