Frankia

Abstract

AbstractFran.ki.a. N.L. fem. n.Frankianamed after Albert Bernhard Frank (1839–1900), a Swiss plant biologist, who studied extensively nitrogen nutrition in legumes and the microorganisms causing root nodulation from 1877 to 1892 and who coined the term “symbiosis.”Actinobacteria / Actinobacteria / Frankiales / Frankiaceae / FrankiaA group of soil‐inhabiting mesophilic, mostly nitrogen‐fixing, organisms in symbiosis with pioneer plants collectively called “actinorhizal plants” in orders Cucurbitales, Fagales, and Rosales.Frankiaisolates have branched septate hyphae, multilocular sporangia, and for the most part vesicles or diazo‐vesicles, specialized cells where nitrogen fixation takes place. AllFrankiastrains sporulate in culture, but only some genotypes maintain the capacity to form abundant sporangia within plant cells. Around 50% of endophyticFrankiahave resisted isolation. Growth is slow, and it took a long time to obtain isolates after decades of unsuccessful attempts. Isolates are mostly white, sometimes pigmented, have mostly simple growth requirements, and can fix nitrogen in pure culture or in symbiotic nodules except for a small number of nonsymbiotic isolates. The genus comprises 11 species and 2 candidatus grouped into four phylogenetic clusters at the root of aerobic actinobacteria.DNA G+C content (mol%): 67.9–72.8.Type species:Frankia alni(Woronin 1866) Von Tubeuf 1895AL.