Frankia

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.[https://frankia.mcb.uconn.edu Frankia and Actinorhizal Plants]

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.

Frankia can resist low concentration of heavy metals such as, Cu, Co, and Zn.{{Cite journal|last1=Abdel‐lateif|first1=Khalid Salah El dein|last2=Mansour|first2=Samira R.|last3=El‐Badawy|first3=Mohamed F.|last4=Shohayeb|first4=Mohamed M.|date=2018|title=Isolation and molecular characterization of Frankia strains resistant to some heavy metals|journal=Journal of Basic Microbiology|volume=58|issue=9|pages=720–729|doi=10.1002/jobm.201800122|pmid=29962068|s2cid=49639716|issn=1521-4028}} 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.{{Cite journal|last1=El dein Abdel-lateif|first1=Khalid Salah|last2=Mansour|first2=Samira R.|last3=El-Badawy|first3=Mohamed F.|last4=Shohayeb|first4=Mohamed M.|date=September 2018|title=Isolation and molecular characterization of Frankia strains resistant to some heavy metals|journal=Journal of Basic Microbiology|volume=58|issue=9|pages=720–729|doi=10.1002/jobm.201800122|pmid=29962068|s2cid=49639716}}{{clarify|reason=Last two sentences incoherent.|date=May 2022}}

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.{{Cite journal|last1=Nouioui|first1=Imen|last2=Ghodhbane-Gtari|first2=Faten|last3=del Carmen Montero-Calasanz|first3=Maria|last4=Rohde|first4=Manfred|last5=Tisa|first5=Louis S.|last6=Gtari|first6=Maher|last7=Klenk|first7=Hans-Peter|date=2017-03-01|title=Frankia inefficax sp. nov., an actinobacterial endophyte inducing ineffective, non nitrogen-fixing, root nodules on its actinorhizal host plants|journal=Antonie van Leeuwenhoek|volume=110|issue=3|pages=313–320|doi=10.1007/s10482-016-0801-7|pmid=27830471|s2cid=39458226|issn=1572-9699}}

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.{{Cite journal|last1=Srivastava|first1=Amrita|last2=Singh|first2=Anumeha|last3=Singh|first3=Satya S.|last4=Mishra|first4=Arun K.|date=2017-04-16|title=Salt stress–induced changes in antioxidative defense system and proteome profiles of salt-tolerant and sensitive Frankia strains|journal=Journal of Environmental Science and Health, Part A|volume=52|issue=5|pages=420–428|doi=10.1080/10934529.2016.1270672|issn=1093-4529|pmid=28085556|s2cid=38519293}} 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|date=April 2023}}

{{Main|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 Dryas{{cite book |last1=Schwintzer |first1=C. R. |last2=Tjepkema |first2=J. |title=The Biology of Frankia and Actinorhizal Plants |date=1990 |publisher=Academic Press |location=San Diego |isbn=978-0126332100}}

File:Frankia Longitudinal Section Toluidine Blue- Atchison, Black.png

Frankia forms nodules via two methods of root infection, intercellularly and intracellularly.{{Cite journal |last=Santi |first=Carole |last2=Bogusz |first2=Didier |last3=Franche |first3=Claudine |date=2013-03-10 |title=Biological nitrogen fixation in non-legume plants |url=http://dx.doi.org/10.1093/aob/mct048 |journal=Annals of Botany |volume=111 |issue=5 |pages=743–767 |doi=10.1093/aob/mct048 |issn=1095-8290|pmc=3631332 }} 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.

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.

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN){{cite web |author=A.C. Parte |url=https://lpsn.dsmz.de/genus/frankia |title=Frankia |access-date=2025-02-28 |publisher=List of Prokaryotic names with Standing in Nomenclature (LPSN) |display-authors=et al.}} and National Center for Biotechnology Information (NCBI).{{cite web |author=C.L. Schoch |url=https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Tree&id=1854&lvl=3&lin=f&keep=1&srchmode=1&unlock |title=Frankia |access-date=2025-02-28 |publisher=National Center for Biotechnology Information (NCBI) taxonomy database |display-authors=et al.}}

Species incertae sedis:

• F. nepalensis Nouioui et al. 2023

• List of bacterial orders
• List of bacteria genera

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{{Bacteria classification}}

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Category:Actinomycetia

Category:Bacteria genera