Explanation

$Rhizobium\ leguminosarum$is a small, flagellate Gram negative, aerobic, rod-shaped bacteria. It persists saprophytically in the soil until it infects a root hair or damaged epidermal cell. After infection, $Rhizobium$ establishes a symbiotic relationship with legumes living inside the root nodules and fixes large amount of nitrogen, much of which is made available to the plant.