BIODIVERSITY OF RHIZOBIA ISOLATED FROM A WIDE-RANGE OF FOREST LEGUMESIN BRAZIL

Tropical forests have a high diversity of plant species; are they asso ciated with a correspondingly rich microbial flora? We addressed this question by examining the symbiotic rhizobium bacteria that nodulate a diverse pool of forest legume species in Brazil. The 44 strains studi ed had been isolated from 29 legume tree species representing 13 tribe s including all three subfamilies of the Leguminosae, and were chosen to represent major groups from a larger sample that had previously bee n characterized by SDS-PAGE of total proteins. Partial 16S rRNA gene s equence was determined, corresponding to positions 44-303 in the Esche richia coli sequence. Fifteen sequences were found, including six nove l ones. However, all but one of them could be assigned to a genus beca use they grouped closely with sequences from previously described rhiz obial species. Fast-growing strains had sequences similar to Rhizobium spp., Sinorhizobium spp. or Mesorhizobium spp., while the slow-growin g strains had sequences similar to Bradyrhizobium spp. One strain with an intermediate growth rate had a unique sequence which indicated tha t the strain might belong to the genus Azorhizobium. Although the stra ins showed a variety of sequences, it was surprising that these strain s isolated from taxonomically very diverse host plants in previously u nexplored environments were mostly very similar to strains described p reviously, largely from agricultural systems.