Rhizobial isolates that were obtained from both surface and deep soil samples in the Sahelian and Sudano-Guinean areas of Senegal (West Africa) under trees were compared with representative strains of known rhizobial species and genera. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of proteins was used to determine the taxonomic positions of these organisms and the relationships between isolates obtained from the surface and isolates obtained from deep soil. Most of the isolates belonged to eight electrophoretic clusters containing representative strains of , and sp. Isolates were also characterized by the Biolog system, and the results were compared with the results obtained by SDS-PAGE of total proteins; the level of correlation was very low. DNA-rRNA hybridizations with 16S or 23S rRNA from LMG 6138 (T = type strain) confirmed that most of the protein electrophoretic clusters belong in the rRNA complex. Sequencing of 16S rRNA genes showed that some of the -nodulating isolates belong to a separate lineage together with representatives of other protein electrophoretic clusters. Other isolates that belong to the same electrophoretic cluster as the type strain of are considered members of the lineage represented by this type strain. The first lineage is as far removed from as it is from the genus , and the genus The possible relationship among electrophoretic group, geographic origin, and depth of isolation at a particular site is discussed.


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