Diversity of Partial 16S rRNA Sequences Among and Within Strains of African Rhizobia Isolated from Acacia and Prosopis

Summary To assess the phylogenetic diversity of fast-growing rhizobium strains isolated from root nodules of Acacia senegal and Prosopis chilensis trees growing in Sudan and Kenya, a 230-nucleotide segment of the 16S ribosomal RNA gene was sequenced from each of thirty strains. Twelve different sequences were found: four were identical to those of previously described species, eight were novel. Sequence comparisons indicated that one strain belonged to the Rhizobium huakuii phylogenetic branch, while the rest were Sinorhizobium , as they were close to S. (Rhizobium) meliloti, S. f redii, S. teranga and S. saheli . Isolates from Acacia and from Prosopis often had the same sequence, but the sequence type was not very well correlated with the phenotypic characteristics determined previously for these strains. One isolate had two 16S rRNA sequences, differing at six positions, in approximately equal copy number. The type strain of S. saheli was also shown to have two different sequences.