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An alder root nodule gall.JPG
An alder root nodule.
Scientific classification e
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

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.[6] 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.[7]

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.[8]

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.[8]

Frankia can resist low concentration of heavy metals such as, Cu, Co, and Zn.[9] 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.[10][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.[11]

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.[12] 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.

Symbiont plants[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. ^ Normand P, Nguyen TV, Battenberg K, Berry AM, Heuvel BV, Fernandez MP, 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.{{cite journal}}: CS1 maint: uses authors parameter (link)
  4. ^ Normand P, Nouioui I, Pujic P, Fournier P, Dubost A, Schwob G, Klenk HP, Nguyen A, Abrouk D, Herrera-Belaroussi A, Pothier JF, Pflüger V, Fernandez MP. (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.{{cite journal}}: CS1 maint: uses authors parameter (link)
  5. ^ Euzéby JP, Parte AC. "Frankia". List of Prokaryotic names with Standing in Nomenclature (LPSN). Retrieved June 16, 2021.{{cite web}}: CS1 maint: uses authors parameter (link)
  6. ^ Pawlowski, Katharina (2009-06-17). Prokaryotic Symbionts in Plants. Springer Science & Business Media. p. 107. ISBN 9783540754602.
  7. ^ Frankia taxonomy
  8. ^ a b Frankia and Actinorhizal Plants
  9. ^ 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.
  10. ^ 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.
  11. ^ 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.
  12. ^ 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.
  13. ^ Schwintzer & Tjepkema 1990