Comparison of sequence analysis of 16S-23S rDNA spacer regions, AFLP analysis and DNA-DNA hybridizations in Bradyrhizobium

The sequences of the 16S-23S rDNA intergenic spacer region of 62 strains of Bradyrhizobium, including representatives of the three valid species, were determined. The majority of strains had a single rRNA operon type and all contained a tRNA(Ala) and a tRNA(Ile) gene. Analysis of the sequence data p roduced groupings in line with previously obtained AFLP data. DNA-DNA hybri dizations were performed to determine to what extent spacer sequences and A FLP profiles reflected the overall genomic similarities. Strains belonging to the same AFLP group, and strains with spacer sequences diverging less th an 4%, were found to belong to the same genospecies. More remote relationsh ips (DNA homology levels of 40-60 %) between species were reflected in the spacer sequence analysis, but not in the AFLP analysis. For the genus Brady rhizobium, 16S-23S rDNA spacer sequence analysis provides taxonomic informa tion similar, but not always identical to that obtained by DNA-DNA hybridiz ations. Our results indicate that this genus consists of a group of four hi ghly related genospecies (Bradyrhizobium japonicum, Bradyrhizobium liaoning ense and two other genospecies) and at least three other genospecies, one o f which is Bradyrhizobium elkanii.