[A study on taxonomy of Rhizobia isolated from Astragalus sp]

Thirty-six strains isolated from root nodule of Astragalus spp., in comparison with 31 reference strains of Rhizobium, Bradyrhizobium and Sinorhizobium species, and some other strains isolated from legumes in Xinjiang and Hainian Province, were classified by performing numberical taxonomy, DNA-DNA hybrization and partial 16S rRNA gene sequencing. Results of herichical analysis showed most of trains isolated from Astragalus spp. fell into subgroups 8 and 9, Also the DNA homolgy among strains of subgroups 8 and 9 are more than 70%, with the exception of strains CA8593 and SX044, and the DNA homology between strain CA8561, JL84 and type strains of all described rhizobial species are less than 56%. These results indicated that these two subgroups 8 and 9 were unique DNA homologous groups, distinguishing from all described rhizobial species. Sequencing of partial 16S rRNA gene showed that cetrostrain CA8561 of subgroup 8 is phylogenetically far from all know species of Rhizobium, Bradyrhizobium, Sinorhizobium, Azorhizobium and Agrobacterium, and it is a unique geneline. The cetrostrain JL84 of subgroup 9 has a unique position in the phylogenetic branch consisted of species of Rhizobium and Agrobacterium.