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Fifty-eight new isolates were obtained from root nodules of common bean (#Phaseolus vulgaris$) cultivated in soils originating from different agroecological areas in Senegal and Gambia (West Africa). A polyphasic approach including both phenotypic and genotypic techniques was used to study the diversity of the 58 #Rhizobium$ isolates and to determine their taxonomic relationships with reference strains. All the techniques performed, analysis of multilocus enzyme electrophoretic patterns, SDS-PAGE profiles of total cell proteins, PCR-RFLP analysis of the genes encoding 16S rRNA and of the 16S-23S RNA intergenic spacer region (ITS-PCR-RFLP), auxanographic tests using API galleries and nodulation tests lead to the consensus conclusion that the new rhizobial isolates formed two main distinct groups, I and II, belonging to #Rhizobium tropici$ type B and #Rhizobium etli$, respectively. By MLEE #R. etli$ and group II strains showed several related electrophoretic types, evidencing some extent of internal heterogeneity among them. This heterogeneity was confirmed by other techniques (ITS-PCR-RFLP, SDS-PAGE and host-plant-specificity) with the same nine distinct strains of group II showing some differences from the core of group II (54 strains). (Résumé d'auteur)

SDS-PAGE of total bacterial proteins was applied to the classification of 25 Sudanese and five Kenyan strains isolated from the root nodules of #Acacia senegal$ and #Prosopis chilensis$. Twenty strains were also studied by multilocus enzyme electrophoresis (MLEE) and the whole 16S rRNA gene was sequenced from two strains representing the two major clusters. These results, together with the previuously reported numerical taxonomy analysis, pulsed-field gel electrophoresis studies, DNA-DNA dot-blot hybridisation, genomic fingerprinting using repetitive sequence-basec PCR, DNA base composition analysis, DNA-DNA reassociation analysis, partial sequencing of the 16S rRNA gene and RFLP analysis of the amplified 16S rRNA gene, showed that all 30 strains belong to the genus #Sinorhizobium$. Two of the strains grouped with #Sinorhizobium saheli$ and seven with #Sinorhizobium terangae$, while the rest did not cluster with any of the established species. The majority of the strains formed two phenotypically and genotypically distinct groups and we therefore propose that these strains should be classified as two new species, #Sinorhizobium arboris$ sp. nov. and #Sinorhizobium kostiense$ sp. nov. (Résumé d'auteur)