''Frankia'' is a genus of nitrogen-fixing

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

that live in

symbiosis Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or para ...

with

actinorhizal plant Actinorhizal plants are a group of angiosperms characterized by their ability to form a symbiosis with the nitrogen fixing actinomycetota ''Frankia''. This association leads to the formation of nitrogen-fixing root nodules. Classification Actinor ...

s, similar to the ''

Rhizobium ''Rhizobium'' is a genus of Gram-negative soil bacteria that fix nitrogen. ''Rhizobium'' species form an endosymbiotic nitrogen-fixing association with roots of (primarily) legumes and other flowering plants. The bacteria colonize plant cells ...

'' bacteria found in the root nodules of

legume A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock for ...

s in the family

Fabaceae The Fabaceae or Leguminosae,International Code of Nomenc ...

. ''Frankia'' also initiate the forming of

root nodule Root nodules are found on the roots of plants, primarily legumes, that form a symbiosis with nitrogen-fixing bacteria. Under nitrogen-limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria known a ...

s. This genus was originally named by

Jørgen Brunchorst Jørgen Brunchorst (10 August 1862 – 19 May 1917) was a Norwegian natural scientist, politician and diplomat. Biography Brunchorst was born in Bergen, the son of ship builder and – captain Christian Ege Brunchorst (1835–64) and his wife E ...

, in 1886 to honor the German biologist

Albert Bernhard Frank Albert Bernhard Frank (January 17, 1839 – September 27, 1900) was a German botanist, plant pathologist, and mycologist, born in Dresden. He is credited with coining the term ''mycorrhiza'' in his 1885 paper "Über die auf Wurzelsymbiose beruhen ...

. Brunchorst considered the organism he had identified to be a filamentous fungus. redefined the genus in 1970 as containing

prokaryotic A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...

actinomycetes The Actinomycetales is an order of Actinomycetota. A member of the order is often called an actinomycete. Actinomycetales are generally gram-positive and anaerobic and have mycelia in a filamentous and branching growth pattern. Some actinomycete ...

and created the family

Frankiaceae ''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 ...

within the

Actinomycetales The Actinomycetales is an order of Actinomycetota. A member of the order is often called an actinomycete. Actinomycetales are generally gram-positive and anaerobic and have mycelia in a filamentous and branching growth pattern. Some actinomycetes ...

. He retained the original name of ''Frankia'' for the genus.

Overview

Most ''Frankia'' strains are specific to different plant species. The bacteria are filamentous and convert atmospheric nitrogen into ammonia via the

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

nitrogenase Nitrogenases are enzymes () that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the reduction of nitrogen (N2) to ammonia (NH3). Nitrogenases are the only fa ...

, a process known as

nitrogen fixation Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...

. 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.Frankia and Actinorhizal Plants
/ref> Several ''Frankia'' genomes are now available which may help clarify how the symbiosis between

prokaryote A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Conne ...

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. ''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. ''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. ''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. 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

* All species in the genus ''

Alnus Alders are trees comprising the genus ''Alnus'' in the birch family Betulaceae. The genus comprises about 35 species of monoecious trees and shrubs, a few reaching a large size, distributed throughout the north temperate zone with a few sp ...

'' in the family

Betulaceae Betulaceae, the birch family, includes six genera of deciduous nut-bearing trees and shrubs, including the birches, alders, hazels, hornbeams, hazel-hornbeam, and hop-hornbeams numbering a total of 167 species. They are mostly natives of the ...

* Some species in all four genera in the family

Casuarinaceae The Casuarinaceae are a family of dicotyledonous flowering plants placed in the order Fagales, consisting of four genera and 91 species of trees and shrubs native to eastern Africa, Australia, Southeast Asia, Malesia, Papuasia, and the Pacifi ...

* Certain species in the genus ''

Coriaria ''Coriaria'' is the sole genus in the family Coriariaceae, which was described by Linnaeus in 1753. It includes 14 species of small trees, shrubs and subshrubs, with a widespread but disjunct distribution across warm temperate regions of the w ...

'' in the family

Coriariaceae ''Coriaria'' is the sole genus in the family Coriariaceae, which was described by Linnaeus in 1753. It includes 14 species of small trees, shrubs and subshrubs, with a widespread but disjunct distribution across warm temperate regions of the wor ...

* '' Datisca cannabina'' and ''

Datisca glomerata ''Datisca glomerata'' is a species of plant native to California, Nevada, and Baja California known by the common name Durango root. It is one of only two to four species in the plant family Datiscaceae. It is an erect perennial herb with distin ...

'' in the family

Datiscaceae The Datiscaceae are a family of dicotyledonous plants, containing two species of the genus ''Datisca''. Two other genera, '' Octomeles'' and '' Tetrameles'', are now classified in the family Tetramelaceae. Datiscaceae are large herbaceous plant ...

* All species in the three genera in the family

Elaeagnaceae The Elaeagnaceae are a plant family, the oleaster family, of the order Rosales comprising small trees and shrubs, native to temperate regions of the Northern Hemisphere, south into tropical Asia and Australia. The family has about 60 species ...

, ''

Elaeagnus ''Elaeagnus'' , silverberry or oleaster, is a genus of about 50–70 species of flowering plants in the family Elaeagnaceae. Description ''Elaeagnus'' plants are deciduous or evergreen shrubs or small trees. The alternate leaves and the shoo ...

'', ''

Shepherdia ''Shepherdia'', commonly called buffaloberry or bullberry, is a genus of small shrubs in the Elaeagnaceae family. The plants are native to northern and western North America. They are non-legume nitrogen fixers. ''Shepherdia'' is dioecious, wit ...

'', and ''

Hippophae ''Hippophae'' is the genus of sea buckthorns, deciduous shrubs in the family Elaeagnaceae. The name sea buckthorn may be hyphenated to avoid confusion with the unrelated true buckthorns (''Rhamnus'', family Rhamnaceae). It is also referred to ...

'' * All species in the genera ''

Myrica ''Myrica'' is a genus of about 35–50 species of small trees and shrubs in the family Myricaceae, order Fagales. The genus has a wide distribution, including Africa, Asia, Europe, North America and South America, and missing only from Austra ...

'', '' Morella'', and '' Comptonia'' in the family

Myricaceae The Myricaceae are a small family of dicotyledonous shrubs and small trees in the order Fagales. There are three genera in the family, although some botanists separate many species from ''Myrica'' into a fourth genus ''Morella''. About 55 speci ...

. * 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 ''Chamaebatia'', also known as mountain misery, is a genus of two species of aromatic evergreen shrubs endemic to California. Its English common name derives from early settlers' experience with the plant's dense tangle and sticky, strong-smell ...

'', and some species of '' Dryas''

References

{{Taxonbar, from=Q134931 Actinomycetia Bacteria genera