PCR-RFLP AND TOTAL DNA HOMOLOGY REVEALED 3 RELATED GENOMIC SPECIES AMONG BROAD-HOST-RANGE FRANKIA STRAINS

Restriction fragment length polymorphism (RFLP) analysis of the PCR am plified nifD-K intergenic spacer (IGS) region was used to cluster 22 F rankia strains of the Elaeagnus host specificity group into seven geno mic groups and to measure the degree of genetic similarity among them. This PCR-RFLP analysis could assign freshly isolated strains to descr ibed genomic species and revealed genomic groups not yet described amo ng Frankia strains of the Elaeagnus specificity group. Six broad-host- range Frankia strains, infective on both Alnus and Elaeagnus, fell int o three closely related PCR-RFLP clusters, DNA-DNA hybridization was t hen used to establish the correlations between PCR-RFLP clusters and t otal DNA relatedness groups. The three PCR-RFLP clusters agreed with t wo new and one reference genomic species, indicating that Frankia abil ity to nodulate with Alnus and Elaeagnus is a monophyletic trait share d by three genomic species.