GROUPING OF FRANKIA STRAINS ON THE BASIS OF SUSCEPTIBILITY TO ANTIBIOTICS, PIGMENT PRODUCTION AND HOST-SPECIFICITY

Thirty-nine selected Frankia strains belonging to different genomic sp ecies were clustered on the basis of their in vitro susceptibility to 17 antibiotics, pigment production and ability to nodulate plants of t he genus Alnus and/or the family Elaeagnaceae, or the family Casuarina ceae. The majority of the strains studied fell into three cluster grou ps. A, E and C, corresponding to the three host-specificity groups, Al nus, Elaeagnus and Casuarina. Within the groups, eight composite clust ers, consisting of at least two strains, and five single-member cluste rs were recovered at the 0.74 distance level, in good agreement with l evels of genetic relatedness between the strains. In addition, five st rains were recovered as single-member clusters not in the cluster grou ps, four of them representing single-member genospecies and one strain not assigned to any known genospecies. The concordance between the ph enotypic clusters and the genospecies described previously shows that the grouping may reflect the taxonomic structure of the genus Frankia. For some clusters, differentiating phenotypic characters were found w hich may be useful for species definition.