Frankia saprophytica sp. nov., an atypical, non-infective (Nod-) and non-nitrogen fixing (Fix-) actinobacterium isolated from Coriaria nepalensis root nodules.

Strain CN3, a Coriaria nepalensis isolate, appears to form hyphae and sporangia typical of members fo the genus Frankia. However, it failed to form vesicles, to reduce acetylene and to induce nodules on its original host plant. A polyphasic approach was used here to determine the taxonomic status of strain CN3. The 16S rRNA gene sequence of strain CN3 showed the highest sequence identity with Frankia asymbiotica type strain M16386 (99.4 %). Digital DNA-DNA hybridization between strains CN3 and M16386 was 25.7 %, which is clearly below the accepted cut-off point of 70 %. The G+C content of DNA was 71.8 mol%. Whole-cell hydrolysates of strain CN3 were rich in meso-diaminopimelic acid. Cell-wall sugars were composed of galactose, glucose, mannose, rhamnose and traces of ribose. The polar lipid profile contained phosphatidylinositol, phosphatidylglycerol, diphosphatidylglycerol, phosphoglycolipids, phospholipid, six uncharacterized glycolipids and two uncharacterized lipids. The predominant menaquinone (>25 %) was MK-9(H6). Major fatty acids (>15 %) of strain CN3 consisted of iso-C16 : 0, C17 : 1ω8c and C15 : 0. Based on 16S rRNA gene phylogeny, genome sequence analysis and phenotypic results, strain CN3 (=DSM 105290=CECT 9314) is proposed to represent the type strain of a novel species, Frankia saprophytica sp. nov.