03017naa a2200157 a 450000100080000000500110000800800410001910000190006024501100007926000090018930000140019850000370021252024480024970000160269777301460271314659322005-11-21       2003    bl uuuu     u00u1 u    #d1 aGERMANO, M. G.  aRibosomal phylogeny of a brazilian collection of bradyrhizobium symbionts of thirty-three legume species.  c2003  c1 CD-ROM.  aSeção: Microbiologia de Solos.  aMany species of the family Leguminosae (Fabaceae) establish effective symbioses with N2-fixing bacteria in the genus Bradyrhizobium, which is relatively poorly studied despite wide geographic distribution and legume-host range. Genetic diversity seems to be greater in tropical than in temperate species of rhizobia, thus three ribosomal regions of a Brazilian culture collection of 119 strains of Bradyrhizobium, isolated from thirty-three legume species, representing nine tribes and all three subfamilies, were analyzed by RFLP-PCR. For the 16S rRNA gene, reference strains of B. japonicum fit into two major clusters, joined at a level of similarity of 50%, which included forty-seven strains, 90% of which were isolated from soybean, while two other clusters, joined at a similarity of 53%, were composed of strains of B. elkanii. Furthermore, three other major clusters were identified in which all strains were clustered at a final level of similarity of only 28%. For the intergenic spacer region (ITS), strains were clustered at a final level of similarity of 27%; reference strains of B. japonicum fit into a major group at 37% of similarity that included fifty-six strains, 84% isolated from soybean, while strains of B. elkanii fit into another major group, at a 44% level of similarity, clustering fifty-three strains, 64% isolated from other hosts than soybean. New clusters were also observed for the ITS region. The highest variability was detected in the analysis of the 23S rRNA gene with many distinct clusters and a very low level of similarity (16%) in the final grouping of the strains. A polyphasic approach, considering the three ribosomal regions, confirmed two great groups, related to B. japonicum and B. elkanii, at similarity levels of 54 and 46%, respectively. However, subclusters were defined within those two groups, and might be related to intraspecific variability, or to new subspecies, or even to new species. Furthermore, at least two new clusters were observed that might represent new species. The majority of strains isolated from soybean fit into the species B. japonicum, while most strains isolated from Brazilian legume species fit into B. elkanii or into the new clusters. The collection of bradyrhizobia analyzed in this study showed a genetic variability never reported before, confirming a high level of diversity of rhizobia in the tropics. Partially financed by CNPq (PRONEX-and 520396/96-0).1 aHUNGRIA, M.  tIn: CONGRESSO BRASILEIRO DE MICROBIOLOGIA, 22., 2003, Florianópolis. [Resumos]. Florianópolis: Sociedade Brasileira de Microbiologia, 2003.