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Preparation and Fractionation of Rhizobium Bacteroids by Zone Sedimentation through Sucrose Gradients

^a Plant Physiology Division, Department of Scientific and Industrial Research, Private Bag, Palmerston North, New Zealand

Zone sedimentation through sucrose gradients was used for preparing Rhizobium bacteroids from lupin nodules and for separating them into slowly and rapidly sedimenting fractions.

The purity of the bacteroids was established by electron microscopy and by enzyme assays, and they were shown to contain a CO-insensitive cytochrome c oxidase.

Bacteroids sedimented more rapidly than broth-cultured Rhizobium bacteria, and bacteroids from old nodules sedimented more rapidly than bacteroids from young nodules.

There appear to be at least two forms of bacteroid in old nodules: slowly sedimenting bacteroids with moderate colony-forming ability resembling the bacteroids found in young nodules, and rapidly sedimenting bacteroids with much lower colony-forming ability.