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An alder root nodule.
Scientific classification Edit this classification
Domain: Bacteria
Phylum: Actinomycetota
Class: Actinomycetia
Order: Frankiales
Family: Frankiaceae
Becking 1970 (Approved Lists 1980)[2]
Genus: Frankia
Brunchorst 1886[1]
Type species
Frankia alni
(Woronin 1866) Von Tubeuf 1895 non Steud. 1840

See text

  • Frankiella Maire and Tison 1909 non von Speschnew 1900 non Racheboeuf 1983
  • Parafrankia Gtari 2023
  • Protofrankia Gtari 2023
  • Pseudofrankia Gtari 2023

Frankia is a genus of nitrogen-fixing bacteria that live in symbiosis with actinorhizal plants, similar to the Rhizobium bacteria found in the root nodules of legumes in the family Fabaceae. Frankia also initiate the forming of root nodules.

This genus was originally named by Jørgen Brunchorst, in 1886 to honor the German biologist Albert Bernhard Frank.[4] Brunchorst considered the organism he had identified to be a filamentous fungus. Becking [de; nl] redefined the genus in 1970 as containing prokaryotic actinomycetes and created the family Frankiaceae within the Actinomycetales. He retained the original name of Frankia for the genus.[5]

A section through an alder root nodule


Most Frankia strains are specific to different plant species. The bacteria are filamentous and convert atmospheric nitrogen into ammonia via the enzyme nitrogenase, a process known as nitrogen fixation. They do this while living in root nodules on actinorhizal plants. The bacteria can supply most or all of the nitrogen requirements of the host plant. As a result, actinorhizal plants colonise and often thrive in soils that are low in plant nutrients.[6]

Several Frankia genomes are now available which may help clarify how the symbiosis between prokaryote and plant evolved, how the environmental and geographical adaptations occurred, the metabolic diversity, and the horizontal gene flow among the symbiotic prokaryotes.[6]

Frankia can resist low concentration of heavy metals such as, Cu, Co, and Zn.[7] Frankia may be an advantage for degraded soil. Degraded soil is known as soil that is heavy metal rich or nutrient depleted due to a drought. Frankia is a nitrogen-fixed organism, explaining why it is able to resist heavy metals.[8][clarification needed]

Frankia is a gram-positive Bacteria that is found on the roots of plants. The fact that Frankia is gram-positive means that the bacteria is made up of thick cell walls made out of protein called peptidologlycan. This helps with the resistance of the heavy metals that may be in the degraded soil.[9]

Frankia tolerates a narrow range of temperatures and soil pH levels. It grows best at around 30 degrees Celsius with an environment pH between 6.5 and 7.[10] These facts shows that Frankia is very sensitive to its environment. Though Frankia would not be suitable for all agriculture it does demonstrate possibilities in select areas, or in temperature controlled environments.[citation needed]

Symbiont plants[edit]


The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)[3] and National Center for Biotechnology Information (NCBI)[12]

16S rRNA based LTP_08_2023[13][14][15] 120 marker proteins based GTDB 08-RS214[16][17][18]

F. coriariae Nouioui et al. 2017


F. casuarinae Nouioui et al. 2016

F. canadensis Normand et al. 2018[19]

F. umida Normand et al. 2023

F. torreyi Nouioui et al. 2019

F. alni (Woronin 1866) Von Tubeuf 1895

"F. gtarii" Nouioui et al. 2023

"F. tisai" Nouioui et al. 2023


F. inefficax Nouioui et al. 2017

F. asymbiotica Nouioui et al. 2017

F. saprophytica Nouioui et al. 2018


F. discariae Nouioui et al. 2017

F. soli Gtari et al. 2020

F. irregularis Nouioui et al. 2018

F. colletiae Nouioui et al. 2023

F. elaeagni (Schroeter 1886) Becking 1970 ex Nouioui et al. 2016


"Ca. F. meridionalis" Nguyen et al. 2019

"Ca. F. californiensis" Normand et al. 2017[20]

F. coriariae [incl. "Ca. F. datiscae" Persson et al. 2011]


F. inefficax

F. asymbiotica

F. saprophytica


F. discariae

F. soli

F. elaeagni

F. irregularis


F. casuarinae

F. canadensis

"Ca. F. nodulisporulans" Herrera-Belaroussi et al. 2020

"Ca. F. alpina" Pozzi et al. 2020 [incl. "F. subtilis" Brunchorst 1886]

F. alni

F. torreyi

Species incertae sedis:

  • F. nepalensis Nouioui et al. 2023

See also[edit]


  1. ^ Brunchorst J. (1886). "Über einige Wurzelanschwellungen, besonders diejenigen von Alnus und den Elaegnaceen" [On root swellings, particularly those of Alnus and the Elaeagnaceae]. Untersuchungen aus dem botanischen Institut in Tübingen [Investigations of the Botanical Institute in Tübingen ]. 2 (151–177).
  2. ^ Becking JH. (1970). "Frankiaceae fam. nov. (Actinomycetales) with one new combination and six new species of the genus Frankia Brunchorst 1886, 174". International Journal of Systematic Bacteriology. 20: 201–220. doi:10.1099/00207713-20-2-201.
  3. ^ a b A.C. Parte; et al. "Frankia". List of Prokaryotic names with Standing in Nomenclature (LPSN). Retrieved 2023-09-09.
  4. ^ Pawlowski, Katharina (2009-06-17). Prokaryotic Symbionts in Plants. Springer Science & Business Media. p. 107. ISBN 9783540754602.
  5. ^ "Frankia taxonomy". Archived from the original on 2011-07-27. Retrieved 2011-01-14.
  6. ^ a b Frankia and Actinorhizal Plants
  7. ^ Abdel‐lateif, Khalid Salah El dein; Mansour, Samira R.; El‐Badawy, Mohamed F.; Shohayeb, Mohamed M. (2018). "Isolation and molecular characterization of Frankia strains resistant to some heavy metals". Journal of Basic Microbiology. 58 (9): 720–729. doi:10.1002/jobm.201800122. ISSN 1521-4028. PMID 29962068. S2CID 49639716.
  8. ^ El dein Abdel-lateif, Khalid Salah; Mansour, Samira R.; El-Badawy, Mohamed F.; Shohayeb, Mohamed M. (September 2018). "Isolation and molecular characterization of Frankia strains resistant to some heavy metals". Journal of Basic Microbiology. 58 (9): 720–729. doi:10.1002/jobm.201800122. PMID 29962068. S2CID 49639716.
  9. ^ Nouioui, Imen; Ghodhbane-Gtari, Faten; del Carmen Montero-Calasanz, Maria; Rohde, Manfred; Tisa, Louis S.; Gtari, Maher; Klenk, Hans-Peter (2017-03-01). "Frankia inefficax sp. nov., an actinobacterial endophyte inducing ineffective, non nitrogen-fixing, root nodules on its actinorhizal host plants". Antonie van Leeuwenhoek. 110 (3): 313–320. doi:10.1007/s10482-016-0801-7. ISSN 1572-9699. PMID 27830471. S2CID 39458226.
  10. ^ Srivastava, Amrita; Singh, Anumeha; Singh, Satya S.; Mishra, Arun K. (2017-04-16). "Salt stress–induced changes in antioxidative defense system and proteome profiles of salt-tolerant and sensitive Frankia strains". Journal of Environmental Science and Health, Part A. 52 (5): 420–428. doi:10.1080/10934529.2016.1270672. ISSN 1093-4529. PMID 28085556. S2CID 38519293.
  11. ^ Schwintzer, C. R.; Tjepkema, J. (1990). The Biology of Frankia and Actinorhizal Plants. San Diego: Academic Press. ISBN 978-0126332100.
  12. ^ Sayers; et al. "Frankia". National Center for Biotechnology Information (NCBI) taxonomy database. Retrieved 2023-09-09.
  13. ^ "The LTP". Retrieved 20 November 2023.
  14. ^ "LTP_all tree in newick format". Retrieved 20 November 2023.
  15. ^ "LTP_08_2023 Release Notes" (PDF). Retrieved 20 November 2023.
  16. ^ "GTDB release 08-RS214". Genome Taxonomy Database. Retrieved 10 May 2023.
  17. ^ "bac120_r214.sp_label". Genome Taxonomy Database. Retrieved 10 May 2023.
  18. ^ "Taxon History". Genome Taxonomy Database. Retrieved 10 May 2023.
  19. ^ Normand, P; Nouioui, I; Pujic, P; Fournier, P; Dubost, A; Schwob, G; Klenk, HP; Nguyen, A; Abrouk, D; Herrera-Belaroussi, A; Pothier, J.F.; Pflüger, V; Fernandez, M.P. (2018). "Frankia canadensis sp. nov., isolated from root nodules of Alnus incana subspecies rugosa". Int J Syst Evol Microbiol. 68 (9): 3001–3011. doi:10.1099/ijsem.0.002939. PMID 30059001.
  20. ^ Normand P; Nguyen, T.V.; Battenberg, K; Berry, A.M.; Heuvel, B.V.; Fernandez, M.P.; Pawlowski, K. (2017). "Proposal of "Candidatus Frankia californiensis", the uncultured symbiont in nitrogen-fixing root nodules of a phylogenetically broad group of hosts endemic to western North America". Int J Syst Evol Microbiol. 67 (10): 3706–3715. doi:10.1099/ijsem.0.002147. PMID 28884663. S2CID 41316476.