Genetic diversity and phylogeny of Rhizobia that nodulate Acacia spp. in Morocco assessed by analysis of rRNA genes

Forty rhizobia nodulating four #Acacia$ species (#A. gummifera$, #A. raddiana$, #A. cyanophylla$, and #A. horrida$) were isolated from different sites in Morocco. These rhizobia were compared by analyzing both the 16S rRNA gene (rDNA) and the 16S-23S rRNA spacer by PCR with restriction fragment length polymorphism (RFLP) analysis. Analysis of the length of 16S-23S spacer showed a considerable diversity within these microsymbionts, but RFLP analysis of the amplified spacer revealed no additional heterogeneity. Three clusters were identified when 16S rDNA analysis was carried out. Two of these clusters include some isolates which nodulate, nonspecifically, the four #Acacia$ species. These clusters, A and B, fit within the #Sinorhizobium$ lineage and are closely related to #S. meliloti$ and S. fredii$, respectively. The third cluster appeared to belong to the #Agrobacterium$-#Rhizobium galegae$ phylum and is more closely related to the Agrobacterium tumefaciens$ species. These relations were confirmed by sequencing a representative strain from each cluster. (Résumé d'auteur