ISOLATION AND CHARACTERIZATION OF FRANKIA STRAINS FROM CORIARIA-NEPALENSIS

Nine Frankia-like actinomycetes were isolated from root nodules of Coriaria nepalensis. All isolates formed hyphae and sporangia typical of Frankia but failed to induce nodules on Coriaria seedlings or to reduce acetylene in pure culture. Hybridization with a 16S rRNA targeted oligonucleotide probe indicated that the isolates did belong to the genus Frankia. This was confirmed for one of the isolates (Cn7) by comparison of partial 16S rRNA sequences of the cloned amplification products that showed 94.2 and 96.1% homology with those of the confirmed Frankia strains from Alnus (Ag45/Mut15) and Casuarina (ORS 020606), respectively. Similar values were obtained when 16S rRNA sequences of Cn7 were compared with those of the amplification products obtained directly from nodules of Coriaria nepalensis. Analysis of two variable regions of 15 cloned amplification products from nodules showed two types of 16S rRNA sequences, slightly different from each other. In both variable regions, none of the isolates showed identical sequences to those obtained from nodules. The results argue strongly that the isolates are members of the genus Frankia. However, their identity as endophytes of Coriaria nodules could not be proved.