''Frankia'' is a genus of

nitrogen-fixing Nitrogen fixation is a chemical process by which molecular dinitrogen () is converted into ammonia (). It occurs both biologically and abiological nitrogen fixation, abiologically in chemical industry, chemical industries. Biological nitrogen ...

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

that live in

symbiosis Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biological interaction, between two organisms of different species. The two organisms, termed symbionts, can fo ...

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. Actinorhizal plants ar ...

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 ce ...

'' bacteria found in the root nodules of

legume Legumes are plants in the pea family Fabaceae (or Leguminosae), or the fruit or seeds of such plants. When used as a dry grain for human consumption, the seeds are also called pulses. Legumes are grown agriculturally, primarily for human consum ...

s in the family

Fabaceae Fabaceae () or Leguminosae,International Code of Nomen ...

. ''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 ...

s. This genus was originally named by Jørgen Brunchorst, in 1886 to honor the German biologist

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

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

prokaryotic A prokaryote (; less commonly spelled procaryote) is a single-celled organism whose cell lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Ancient Greek (), meaning 'before', and (), meaning 'nut' ...

actinomycetes The Actinomycetales is an Scientific classification, order of Actinomycetota. A member of the order is often called an actinomycete. Actinomycetales are generally Gram-positive bacteria, gram-positive and anaerobic and have mycelia in a filamento ...

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 actinomycet ...

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

Overview

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

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

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 dinitrogen () is converted into ammonia (). It occurs both biologically and abiological nitrogen fixation, abiologically in chemical industry, chemical industries. Biological nitrogen ...

. 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 (; less commonly spelled procaryote) is a unicellular organism, single-celled organism whose cell (biology), cell lacks a cell nucleus, nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Ancient Gree ...

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. The Gram stain ...

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

'' 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 ...

* 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 ...

* Certain species in the genus '' Coriaria'' in the family Coriariaceae * '' Datisca cannabina'' and '' Datisca glomerata'' 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 plants, ...

* 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 in ...

, ''

Elaeagnus ''Elaeagnus'' () is a genus of flowering plants in the family (biology), family Elaeagnaceae. Some species of the genus are commonly known as silverberry or oleaster, Description ''Elaeagnus'' plants are deciduous or evergreen shrubs or smal ...

'', ''

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, wi ...

'', and ''

Hippophae ''Hippophae'', from Ancient Greek ἵππος (''híppos''), meaning "horse", and φάος (''pháos''), meaning "light", is a genus of flowering plants in the family Elaeagnaceae. They are deciduous shrubs. They are exceptionally hardy plants, ...

'' * 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 Antar ...

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

Myricaceae Myricaceae is a small family of dicotyledonous shrubs and small trees in the order Fagales with its type genus ''Myrica'', the sweet gales. There are three genera in the family, although some botanists separate many species from Myrica into a fo ...

. * All species in six genera in the family

Rhamnaceae The Rhamnaceae are a large Family (biology), 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 specie ...

, ''

Ceanothus ''Ceanothus'' is a genus of about 50–60 species of 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 ceanothus. ''"Ceanothus" ...

'', ''

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 fixers. Taxonomy Species ''Colletia'' comprises ...

'', ''

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 t ...

'', and possibly ''

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

'' * Some species in the family

Rosaceae Rosaceae (), the rose family, is a family of flowering plants that includes 4,828 known species in 91 genera. The name is derived from the type genus '' Rosa''. The family includes herbs, shrubs, and trees. Most species are deciduous, but som ...

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 ''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''

Nodule Formation

''Frankia'' forms nodules via two methods of root infection, intercellularly and intracellularly.

Intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...

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.

Phylogeny

The currently accepted taxonomy is based on the

List of Prokaryotic names with Standing in Nomenclature List of Prokaryotic names with Standing in Nomenclature (LPSN) is an online database that maintains information on the naming and taxonomy of prokaryotes, following the taxonomy requirements and rulings of the International Code of Nomenclatu ...

(LPSN) and

National Center for Biotechnology Information The National Center for Biotechnology Information (NCBI) is part of the National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. The NCBI is lo ...

(NCBI). Species incertae sedis: * ''F. nepalensis'' Nouioui et al. 2023

References

{{Authority control Actinomycetia Bacteria genera

Overview

Symbiont plants

Nodule Formation

Phylogeny

See also

References