Identification and phylogenetic classification of Rhizobium species by mapped restriction site polymorphism (MRSP) analysis of PCR-amplified 16S rRNA genes: Application to the characterization of communities isolated directly from soil samples and to the bias generated by analysis of mixed-cultures or mixed-16S rDNAS

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Evaluation of AFLP for the grouping of Bradyrhizobium strains

In recent years we have characterized 250 Bradyrhizobium strains, mainly from Senegal, using several taxonomic techniques i.e. numerical taxonomy of phenotypic features, Biolog system, SDS-PAGE of total cellular proteins, AS rDNA RFLP and sequence analyses, 16S-23S rDNA intergenic gone spacer RFLP and sequence analyses, AFLP, DNA:DNA hybridizations. Here we evaluate the taxonomic resolving power of those techniques by comparing the results obtained on various subsets of the same strains. We conclude that AFLP is a useful method for an initial grouping of Bradyrhizobium strains and provides infraspecific information. However, from a limited comparison, it appears that the less labor-intensive 16S-23S rDNA intergenic gene spacer analysis gives similar results and may provide additional information on deeper groupings

Highlights of nitrogen fixation research

At the present time, the precise taxonomial status of many strains classified as #Bradyrhizobium still remains unclear. There is a need to develop a reliable grouping method, specifying the genetic relationships between these strains. Phenotypic methods as auxanography or protein profiling did not prove valuable for classification of bradyrhizobia and were not in good agreement with phylogenetic data. The purpose of this work is to develop a strategy to analyse the diversity of bradyrhizobia and to identify genomic groups among our collection of strains isolated from 9 small legume species in Senegal. #B. japonicum, #B. elkanii$ and representatives of previously described groups by Moreira et al. (1993) and Dupuy et al. (1994) were included as references. Bacterial diversity was assessed by two different techniques, PCR-RFLP analysis of the IGS region between 16S and 23S rDNA (IGS) and the AFLP technique. Groupings of strains obtained by the two methodologies will be presented and compared. 16S rDNA PCR-RFLP analysis of strains representative of IGS clusters from small legumes was also performed. (Résumé d'auteur

Diversity of bradyrhizobia from 27 tropical Leguminosae species native of Senegal.

We isolated 71 slow-growing bacterial strains from nodules of 27 native leguminous plants species in Senegal (West Africa) belonging to the genera #Abrus, #Alysicarpus, #Bryaspis, #Chamaecrista, #Cassia, #Crotalaria, #Desmodium, #Eriosema, #Indigofera, #Moghania, #Rhynchosia, #Sesbania, #Tephrosia, and #Zornia playing an ecological role and having agronomic potential in arid regions. The isolates were charaterised by restriction fragment length polymorphism (RFLP) analysis of PCR-amplified 165 rDNA and comparative SDS-PAGE of whole-cell proteins ; reference strains of the different known rhizobial species and groups were included as references. We conclude that these nodule isolates are diverse, and form several phylogenetic subgroups inside #Bradyrhizobium$. Nodulation tests performed on 5 plant species demonstrated host specificity among the strains studied. (Résumé d'auteur