DNA-DNA hybridizations were performed between Bradyrhizobium strains, isolated mainly from Faidherbia albida and Aeschynomene species, as well as Bradyrhizobium reference strains. Results indicated that the genus Bradyrhizobium consists of at least 11 genospecies, I to XI. The genospecies formed four subgeneric groups that were more closely related to each other (S 40 % DNA hybridization) than to other genospecies (T 40 % DNA hybridization) : (i) genospecies I (Bradyrhizobium japonicum), III (Bradyrhizobium liaoningense), IV and V ; (ii) genospecies VI and VIII ; (iii) genospecies VII and IX ; and (iv) genospecies II (Bradyrhizobium elkanii), X and XI. Photosynthetic Aeschynomene isolates were found to belong to at least two distinct genospecies in one subgeneric group. DNA-DNA hybridization data are compared with data from amplified fragment length polymorphism analysis and 16S-23S rDNA spacer sequence analysis.

We examined the genotypic diversity of 64 Bradyrhizobium strains isolated from nodules from 27 native leguminous plant species in Senegal (West Africa) belonging to the genera Abrus, Alysicarpus, Bryaspis, Chamaecrista, Cassia, Crotalaria, Desmodium, Eriosema, Indigofera, Moghania, Rhynchosia, Sesbania, Tephrosia, and Zornia, which play an ecological role and have agronomic potential in arid regions. The strains were characterized by intergenic spacer (between 16S and 23S rRNA genes) PCR and restriction fragment length polymorphism (IGS PCR-RFLP) and amplified fragment length polymorphism (AFLP) fingerprinting analyses. Fifty-three reference strains of the different Bradyrhizobium species and described groups were included for comparison. The strains were diverse and formed 27 groups by AFLP and 16 groups by IGS PCR-RFLP. The sizes of the IGS PCR products from the Bradyrhizobium strains that were studied varied from 780 to 1,038 bp and were correlated with the IGS PCR-RFLP results. The grouping of strains was consistent by the three methods AFLP, IGS PCR-RFLP, and previously reported 16S amplified ribosomal DNA restriction analysis. For investigating the whole genome, AFLP was the most discriminative technique, thus being of particular interest for future taxonomic studies in Bradyrhizobium, for which DNA is difficult to obtain in quantity and quality to perform extensive DNA:DNA hybridizations.Due to their nitrogen-fixing symbiosis with soil bacteria collectively named rhizobia, legumes play an important role in the nitrogen cycle, especially in the tropics. They are used to restore or increase soil fertility of degraded soils in intercropping systems, as green manure, and to produce medicinal and commercial by-products. In Senegal (West Africa), many native legumes are important plant resources for many purposes, and they are the only alternatives to the costly and pollutive mineral nitrogen fertilizers used in agriculture. Many of these legumes are well adapted to the local arid climatic conditions. As drought and soil erosion progress, they are still present as colonizers. The family Leguminosae is considered to be of tropical or subtropical origin, and many of the recently proposed new rhizobial species originate from leguminous plants from these zones that had not been previously investigated.After several prospections around the country, we focused on 27 native nodulated leguminous plants species belonging to the genera Abrus, Alysicarpus, Bryaspis, Chamaecrista, Cassia, Crotalaria, Desmodium, Eriosema, Indigofera, Moghania, Rhynchosia, Sesbania, Tephrosia, Zornia, which play an important ecological role and have agronomic potential in arid regions. As very little or no information concerning their associated rhizobia were available so far, we obtained 71 nodule isolates from these legumes in different regions in Senegal and first characterized them by sodium dodecyl sulfate-polyacrylamide gel electrophoresis whole-cell protein profiles and by 16S amplified ribosomal DNA restriction analysis (ARDRA) fing...

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