Evolutionary relationships among the soybean bradyrhizobia reconstructed from 16S rRNA gene and internally transcribed spacer region sequence divergence

From sequence divergence of 16S rRNA genes and the internally transcribed s pacer (ITS) region it is reported that variation in phytogenetic placement exists among the 17 different serotype strains of Bradyrhizobium that have been isolated from nodules of soybean. Evolutionary relationships among the bradyrhizobia were more resolved using reconstructions derived from ITS th an from 16S rRNA gene sequence divergence. Strain USDA 129 was placed toget her with USDA 62, 110, 122 and 126, but did not cluster with USDA 123 and 1 27, with which it shares antigenic determinants. The results from the phylo genetic analysis were supported with data from determinations of genetic di versity among additional strains within each of these serogroups using ampl ified fragment length polymorphism analysis. From these results it was conc luded that strains of serogroup 129 were more similar to strains of serogro ups 62, 110 and 122 than they were to strains of serogroups 123 and 127. Th e serotype strain of Bradyrhizobium japonicum USDA 135 and the type strain for Bradyrhizobium liaoningense possessed identical 16S rRNA gene and ITS r egion sequences. Also, the type strain for B. liaoningense cross-reacted wi th antisera prepared against somatic antigens of USDA 135. Therefore, it wa s not possible to distinguish B. liaoningense from serogroup 135 in our ana lysis of B. japonicum and Bradyrhizobium elkanii.