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Overview

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.³

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.⁴

Frankia can resist low concentration of heavy metals such as, Cu, Co, and Zn.⁵ 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.⁶

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.⁷

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 7.⁸ 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

Main article: Actinorhizal plant

• All species in the genus Alnus in the family Betulaceae
• Some species in all four genera in the family Casuarinaceae
• Certain species in the genus Coriaria in the family Coriariaceae
• Datisca cannabina and Datisca glomerata in the family Datiscaceae
• All species in the three genera in the family Elaeagnaceae, Elaeagnus, Shepherdia, and Hippophae
• All species in the genera Myrica, Morella, and Comptonia in the family Myricaceae.
• All species in six genera in the family Rhamnaceae, Ceanothus, Colletia, Discaria, Trevoa, and possibly Adolphia
• Some species in the family Rosaceae including all the species in the genera Cercocarpus, Cowania, Purshia, Chamaebatia, and some species of Dryas⁹

Nodule Formation

Frankia forms nodules via two methods of root infection, intercellularly and intracellularly.¹⁰ Intracellular infection is characterized by initial root-hair deformation which is then infected by the filamentous Frankia. The Frankia then moves within the root cells and forms a pre-nodule which is characterized by a bump on the root. This then gives rise to a Nodule primordium which feeds the bacteria via the vascular tissue of the plant allowing the nodule to mature.¹¹

In contrast the intercellular infection does not have root hair deformation. Instead, the filamentous Frankia invades the roots in the space between cells on the root. After this invasion a Nodule primordium is created similarly to the intracellular mode of formation and the nodule matures.¹²

Phylogeny

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)¹³ and National Center for Biotechnology Information (NCBI).¹⁴

Species incertae sedis:

• F. nepalensis Nouioui et al. 2023

See also

• List of bacterial orders
• List of bacteria genera

References

1. Pawlowski, Katharina (2009-06-17). Prokaryotic Symbionts in Plants. Springer Science & Business Media. p. 107. ISBN 9783540754602. 9783540754602 ↩

2. "Frankia taxonomy". Archived from the original on 2011-07-27. Retrieved 2011-01-14. https://web.archive.org/web/20110727030311/http://web.uconn.edu/mcbstaff/benson/Frankia/FrankiaTaxonomy.htm ↩

3. Frankia and Actinorhizal Plants https://frankia.mcb.uconn.edu ↩

4. Frankia and Actinorhizal Plants https://frankia.mcb.uconn.edu ↩

5. 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. /wiki/Doi_(identifier) ↩

6. 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. /wiki/Doi_(identifier) ↩

7. 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. /wiki/Doi_(identifier) ↩

8. 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. /wiki/Doi_(identifier) ↩

9. Schwintzer, C. R.; Tjepkema, J. (1990). The Biology of Frankia and Actinorhizal Plants. San Diego: Academic Press. ISBN 978-0126332100. 978-0126332100 ↩

10. Santi, Carole; Bogusz, Didier; Franche, Claudine (2013-03-10). "Biological nitrogen fixation in non-legume plants". Annals of Botany. 111 (5): 743–767. doi:10.1093/aob/mct048. ISSN 1095-8290. PMC 3631332. https://dx.doi.org/10.1093/aob/mct048 ↩

11. Santi, Carole; Bogusz, Didier; Franche, Claudine (2013-03-10). "Biological nitrogen fixation in non-legume plants". Annals of Botany. 111 (5): 743–767. doi:10.1093/aob/mct048. ISSN 1095-8290. PMC 3631332. https://dx.doi.org/10.1093/aob/mct048 ↩

12. Santi, Carole; Bogusz, Didier; Franche, Claudine (2013-03-10). "Biological nitrogen fixation in non-legume plants". Annals of Botany. 111 (5): 743–767. doi:10.1093/aob/mct048. ISSN 1095-8290. PMC 3631332. https://dx.doi.org/10.1093/aob/mct048 ↩

13. A.C. Parte; et al. "Frankia". List of Prokaryotic names with Standing in Nomenclature (LPSN). Retrieved 2025-02-28. https://lpsn.dsmz.de/genus/frankia ↩

14. C.L. Schoch; et al. "Frankia". National Center for Biotechnology Information (NCBI) taxonomy database. Retrieved 2025-02-28. https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Tree&id=1854&lvl=3&lin=f&keep=1&srchmode=1&unlock ↩

15. "The LTP". Retrieved 10 December 2024. https://imedea.uib-csic.es/mmg/ltp/#LTP ↩

16. "LTP_all tree in newick format". Retrieved 10 December 2024. https://imedea.uib-csic.es/mmg/ltp/wp-content/uploads/ltp/LTP_all_10_2024.ntree ↩

17. "LTP_10_2024 Release Notes" (PDF). Retrieved 10 December 2024. https://imedea.uib-csic.es/mmg/ltp/wp-content/uploads/ltp/LTP_10_2024_release_notes.pdf ↩

18. "GTDB release 09-RS220". Genome Taxonomy Database. Retrieved 10 May 2024. https://gtdb.ecogenomic.org/about#4%7C ↩

19. "bac120_r220.sp_labels". Genome Taxonomy Database. Retrieved 10 May 2024. https://data.gtdb.ecogenomic.org/releases/release220/220.0/auxillary_files/bac120_r220.sp_labels.tree ↩

20. "Taxon History". Genome Taxonomy Database. Retrieved 10 May 2024. https://gtdb.ecogenomic.org/taxon_history/ ↩

21. 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. https://doi.org/10.1099%2Fijsem.0.002939 ↩

22. 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. https://doi.org/10.1099%2Fijsem.0.002147 ↩