Differences among strains of Bradyrhizobium in fatty acid-methyl ester analysis

Fatty acid-methyl ester (FAME) and two-dimensional principal component analysis of 89 strains of Bradyrhizobium, most of which were from soybean, distinguished five groups of bradyrhizobia. These included one cluster containing several isolates previously designated as Bradyrhizobium elkanii and two related clusters containing strains previously identified as belonging to Bradyrhizobium japonicum groups IA and IB. Not all of the organisms evaluated clustered with the B. japonicum and B. elkanii strains. A number of Bradyrhizobium strains isolated from soybean in Korea and northern Thailand had FAME profiles so different from the B. japonicum and B. elkanii strains as to warrant separation at the species level. A slow-growing isolate from Lupinus also had a FAME profile very different from those of the other bradyrhizobia. Results obtained in this study were generally in agreement with those obtained using other taxonomic approaches, suggesting that FAME analysis provides a relatively simple and reliable procedure for the initial characterization of Bradyrhizobium isolates.