''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 parasit ...

with actinorhizal plants, similar to the '' Rhizobium'' 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 f ...

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, 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 actinomycetes 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 substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

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.Frankia and Actinorhizal Plants
/ref> 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. ''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 bact ...

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'' 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 ''Datisca cannabina'', called false hemp, is a species of flowering plant in the genus ''Datisca'', family Datiscaceae, native to the Aegean Islands, Crete, Cyprus, Anatolia, the Levant, the Transcaucasus, Iraq, Iran, Central Asia, Afghanistan, P ...

'' 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 The Rhamnaceae are a large family of flowering plants, mostly trees, shrubs, and some vines, commonly called the buckthorn family. Rhamnaceae is included in the order Rosales. The family contains about 55 genera and 950 species. The Rhamnaceae h ...

, ''

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 ''Colletia'' is a genus of flowering plants in the family Rhamnaceae, with five species of spiny shrubs. All species of this genus are native to southern South America. They are non-legume nitrogen fixer Actinorhizal plants are a group of angios ...

'', ''

Discaria ''Discaria'' is a genus of 6 species of flowering plants in the family Rhamnaceae, native to temperate regions of the Southern Hemisphere, in Australia, New Zealand and South America. They are deciduous thorny shrubs or small trees growing to 2 ...

'', ''

Trevoa ''Trevoa'' is a genus of actinorhizal plants; these dicotyledon flora are trees or small shrubs. The genus was first proposed by Miers in 1825, but was not fully described until 1830 by Sir William Jackson Hooker. Genus members are notable for th ...

'', and possibly ''

Adolphia ''Adolphia'' is a genus of shrubs in the buckthorn family containing only two species. These are rigid, thorny, flowering bushes. '' Adolphia californica'' , the ''California prickbush'' or ''California spineshrub'', are native to southern Calif ...

'' * 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 ''Cercocarpus'', commonly known as mountain mahogany, is a small genus of at least nine species of nitrogen-fixing flowering plants in the rose family, Rosaceae. They are native to the western United States and northern Mexico, where they grow i ...

'', '' Cowania'', ''

Purshia ''Purshia'' (bitterbrush or cliff-rose) is a small genus of 5–8 species of flowering plants in the family Rosaceae which are native to western North America. Description ''Purshia'' species form deciduous or evergreen shrubs, typically reach ...

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

References

{{Taxonbar, from=Q134931 Actinomycetia Bacteria genera