Phylogenetic analysis of rhizobia and agrobacteria based on 16S rRNA gene sequences

Abstract

The phylogenetic relationships of members of the genera Rhizobium, Agrobacterium, Bradyrhizobium, and Azorhizobium were studied by direct sequencing of their amplified 16S rRNA genes. Comparative analysis of the sequence data confirmed that the genera Bradyrhizobium and Azorhizobium belong to distinct phylogenetic lineages. The genera Rhizobium and Agrobacterium were found to be phylogenetically heterogeneous, and several subgroupings in which Rhizobium and Agrobacterium species were intermixed were evident. The present findings show that the genus and species definitions of these organisms are in need of revision. Different possibilities for this are discussed in the light of sequencing data.