Frankia inefficax sp nov., an actinobacterial endophyte inducing ineffective, non nitrogen-fixing, root nodules on its actinorhizal host plants

Strain EuI1c(T) is the first actinobacterial endophyte isolated from Elaeagnus umbellata that was shown to be infective on members of Elaeagnaceae and Morella but lacking the ability to form effective root nodules on its hosts. The strain can be easily distinguished from strains of other Frankia species based on its inability to produce vesicles, the specialized thick-walled structures where nitrogen fixation occurs. Chemotaxonomically, strain EuI1c(T) contains phosphatidylinositol, diphosphatidylglycerol, two glycophospholipids and phosphatidylglycerol as phospholipids. The whole cell sugars were composed of glucose, galactose, mannose, ribose, rhamnose and fucose as diagnostic sugars of the species. Major fatty acids were iso-C-16:0, C-17:1 omega 8c and C-15:0 and C-17:0 and the predominant menaquinones were MK-9(H-6), MK-9(H-8) and MK-9(H-4). Analysis of the 16S rRNA gene sequence of strain EuI1c(T) showed 97, 97.4 and 97.9% identity with Frankia elaeagni DSM 46783(T), Frankia casuarinae DSM 45818(T) and Frankia alni DSM 45986(T), respectively. Digital DNA:DNA hybridizations with type strains of the three Frankia species with validly/effectively published names are significantly below 70%. These results warrant distinction of EuI1c(T) (= DSM 45817(T) = CECT 9037(T)) as the type strain of a novel species designated Frankia inefficax sp. nov.