Studies on bacteroid size and nucleic acid content of alfalfa bacteroids fractionated by velocity sedimentation

A velocity sedimentation procedure was described to fractionate bacteroids of alfalfa nodules into four subpopulations. Bacteroids in these subpopulations were different in size and nucleic acid content as determined by microscopy and flow-microfluorometry (FMF). The slowest-sedimenting bacteroids (fraction I) were small and resembled free-living Rhizobium meliloti both in size and nucleic acid content. The fastest-sedimenting bacteroids (fraction IV) were 2 to 3 times longer and contained 3 to 4 times more nucleic acid than the small bacteroids in fraction I and free-living R. meliloti. A positive correlation was established between bacteroid size and relative nucleic acid content of bacteroids in alfalfa nodules.