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Proposal of a type strain for Frankia alni (Woronin 1866) Von Tubeuf 1895, emended description of Frankia alni, and recognition of Frankia casuarinae sp nov and Frankia elaeagni sp nov.

Abstract : Before the establishment of pure cultures, the species Frankia alni, 'Frankia casuarinae' and 'Frankia elaeagni' were proposed to encompass all causal agents of the nitrogen-fixing root nodules of dicotyledonous plants from the genera Alnus, Casuarina or Elaeagnus. The sole Frankia species with a validly published name, the type species F. alni, was described by Woronin (1866) as present in the root of alder. Until now no type strain has been designated for F. alni, even though the absence of a type strain has seriously inhibited the application of modern taxonomic methods to the genus Frankia. Thus, we propose that strain ACN14a(T), isolated in pure culture from Alnus viridis ssp. crispa with morphological properties matching the original description of F. alni, be recognized as the type strain of this species according to Rule 18f of the International Code of Nomenclature of Bacteria. We compared ACN14a(T) to two strains, Ccl3(T) and BMG5.12(T), isolated from Casuarina cunninghamiana and Elaeagnus angustifolia, respectively, based on chemotaxonomy, phenotype microarray data and molecular data retrieved from genome sequences. All three tested strains grew as branched hyphae, produced vesicles and multilocular sporangia containing non-motile spores and metabolized short fatty acids, TCA-cycle intermediates and carbohydrates. Chemotaxonomically, the three strains were indistinguishable with respect to phospholipids (phosphatidylinositol, diphosphatidylglycerol, glycophospholipids and phosphatidylglycerol) and cell-sugar composition (glucose, mannose, ribose, rhamnose, galactose and xylose, with the latter two being diagnostic for the genus). The major fatty acids identified in all three strains were iso-C-16 : 0, C-17 : 1 omega 8C, C-15 : 0, C-17 : 0 and C-16 : 0. ACN14a(T) and BMG5.12(T) also shared C-15 : 1 omega 6c, while C-18 : 1 omega 9c was found to be unique to BMG5.12T. The major menaquinones identified in all three novel type strains were MK-9(H-8), MK-9(H-6) and MK-9(H-4). MK-9(H-2) was shared by ACN14a(T) and BMG5.12(T), while MK-10(H-4) and MK-8(H-4) were only found in BMG5.12(T). Analysis of 16S rRNA gene sequences showed 98.1-98.9 % identity between strains ACN14a(T), Ccl3(T) and BMG5.12(T). Digital DNA-DNA hybridization values between the three type strains were well below 70 %. These results confirm the separation of the strains into three distinct species, Frankia alni, Frankia casuarinae sp. nov. and Frankia elaeagni sp. nov. Thus, we propose ACN14a(T) (=DSM 45986(T)=CECT 9034(T)), Ccl3(T) (=DSM 45818(T)=CECT 9043(T)) and BMG5.12(T) (=DSM 46783(T)=CECT 9031(T)) as the respective type strains.
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Imen Nouioui, Faten Ghodhbane-Gtari, Maria del Carmen Montero-Calasanz, Markus Goeker, Jan P. Meier-Kolthoff, et al.. Proposal of a type strain for Frankia alni (Woronin 1866) Von Tubeuf 1895, emended description of Frankia alni, and recognition of Frankia casuarinae sp nov and Frankia elaeagni sp nov.. International Journal of Systematic and Evolutionary Microbiology, Microbiology Society, 2016, 66, pp.5201-5210. ⟨10.1099/ijsem.0.001496⟩. ⟨hal-01604995⟩



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