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''Frankia'' is a genus of nitrogen-fixing bacteria 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 parasi ...
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 Actinorh ...
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 cell ...
'' 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 fo ...
s in the family
Fabaceae The Fabaceae or Leguminosae,International Code of Nomenc ...
. ''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. 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 & Con ...
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 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 actinomycete ...
. 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 Organic redox reaction, reduction of nitrogen (N2) to ammonia (NH3). Nitrog ...
, 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.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 & Con ...
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 In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bacte ...
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 spe ...
'' in the family Betulaceae * 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 Pacific I ...
* 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 ''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 sho ...
'', '' Shepherdia'', 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'', '' Morella'', and ''
Comptonia ''Comptonia'' may refer to: * ''Comptonia'' (plant), a monotypic genus in the family Myricaceae * ''Comptonia'' (sea star), an extinct genus of echinoderms in the family Goniasteridae {{genus disambiguation ...
'' 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 spe ...
. * All species in six genera in the family Rhamnaceae, ''
Ceanothus ''Ceanothus'' is a genus of about 50–60 species of Actinorhizal plant, nitrogen-fixing shrubs and small trees in the buckthorn family (Rhamnaceae). Common names for members of this genus are buckbrush, California lilac, soap bush, or just ceano ...
'', '' Colletia'', '' Discaria'', '' Trevoa'', and possibly '' Adolphia'' * Some species in the family
Rosaceae Rosaceae (), the rose family, is a medium-sized family of flowering plants that includes 4,828 known species in 91 genera. The name is derived from the type genus ''Rosa''. Among the most species-rich genera are '' Alchemilla'' (270), ''Sorbus ...
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