TAXONOMY: Bacteria -> Terrabacteria group -> Actinobacteria -> Actinobacteria -> Frankiales -> Frankiaceae -> Frankia
Vegetative hyphae with limited to extensive branching, 0.5–2.0 µm in diameter and occasionally wider in older cultures. No aerial mycelium is formed on solid media. Intra- and extracellular pigments may be formed. Gram-stain-positive in healthy cultures; Gram-stain-variable in older cultures. Aerobic to microaerophilic with a respiratory type of metabolism. No growth factors are required. Does not grow under anaerobic conditions. Catalase-positive. Mesophilic. Chemoorganotrophic. Usually very slow-growing with doubling times of 20 h to several days. Most strains are capable of fixing N2 both in vitro and in planta. Nonpathogenic to humans and animals (Gordon et al., 1983).
DNA G+C content (mol%): 66–73 (Tm).
Type species: Frankia alni