First report on the occurrence of the uncultivated cluster 2 Frankia microsymbionts in soil outside the native actinorhizal host range area.

The occurrence of uncultivated Frankia was evaluated in Tunisian soils by a plant-trapping assay using Coriaria myrtifolia seedlings. Despite the lack of this compatible host plant for more than two centuries, soil-borne Frankia cells were detected in one sampled soil as shown by the development of root nodules on 2-year-old seedlings. Based on glnA sequences, Tunisian trapped Frankia strains belong to the uncultivated cluster 2 strains that associate with other Coriaria species and also with Ceanothus, Datisca and Rosaceae actinorhizal species. This is the first report on the occurrence of Frankia cluster 2 strains in soils from areas lacking compatible host plant groups.