''Anabaena'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of filamentous cyanobacteria that exist as

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

. They are known for

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 ...

abilities, and they form

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

relationships with certain plants, such as the

mosquito fern ''Azolla'' (common called mosquito fern, water fern, and fairy moss) is a genus of seven species of aquatic ferns in the family Salviniaceae. They are extremely reduced in form and specialized, having a significantly different appearance to ot ...

. They are one of four genera of cyanobacteria that produce

neurotoxin Neurotoxins are toxins that are destructive to nervous tissue, nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insult (medical), insultsSpencer 2000 that can adversely affect function ...

s, which are harmful to local wildlife, as well as farm animals and pets. Production of these neurotoxins is assumed to be an input into its symbiotic relationships, protecting the plant from

grazing In agriculture, grazing is a method of animal husbandry whereby domestic livestock are allowed outdoors to free range (roam around) and consume wild vegetations in order to feed conversion ratio, convert the otherwise indigestible (by human diges ...

pressure. A

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

sequencing In genetics and biochemistry, sequencing means to determine the primary structure (sometimes incorrectly called the primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which succ ...

project was undertaken by the

United States Department of Energy The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and energy production, the research and development of nuclear power, the military's nuclear w ...

between 1999 and 2005. This project mapped the complete

genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

model organism A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. Mo ...

''Anabaena variabilis'' ATCC 29413, which is 7.2 million base pairs long. A paper detailing the process was published in 2014. The study focused on heterocysts, which convert

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

into

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

. Certain species of ''Anabaena'' have been used on

rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...

paddy fields, proving to be an effective natural

fertilizer A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Man ...

Species

Recent changes

The genus has significant overlap with ''Aphanizomenon''. Despite ''An. variabilis'' having been removed from the genus to form a new ''Trichormus'' 1988, it seems to be phylogenetically placed in ''Anabaena'' (between the "planktic" main-group and the group formed by ''An. augstumalis'' and ''An. oscillarioides''). As a result the position of ''T. variabilis'' and the two species of benthic ''Anabaena'' may be subject to change. The group around ''Trichormus variabilis'' is better-supported by data than grouping it together with main-group ''Anabaena''/''Aphanizomenon'', so it's more likely for the two species to be split out. In addition, the position of ''Trichormus azollae'' needs change. * In 2009, a 42-species group under the "planktic" main-group, determined by 16S rRNA or gas vesicle morphotype, were transferred to '' Dolichospermum''. * In 2010, the genus '' Sphaerospermopsis'' was created, moving away 3 species. 3 more were moved to this genus later. * In 2012, 3 species were moved to the new genus '' Chrysosporum''. One was later moved to '' Umezakia''. Many of sequenced the morphospecies in ''Anabaena'', ''Dolichospermum'', and ''Aphanizomenon'' (ADA clade) are not monophyletic. Work is underway to sequence more genomes from these genera to produce a species classification based on genetic branching.

Nitrogen fixation by ''Anabaena''

Under nitrogen-limiting conditions, vegetative cells differentiate into

heterocysts Heterocysts or heterocytes are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as ''Nostoc'', ''Cylindrospermum'', and '' Anabaena''. They fix nitrogen from dinitrogen (N2) in the air ...

at semiregular intervals along the filaments. Heterocyst cells are terminally specialized for nitrogen fixation. The interior of these cells is micro-oxic as a result of increased respiration, inactivation of O₂-producing photosystem (PS) II, and formation of a thickened envelope outside of the cell wall. Nitrogenase, sequestered within these cells, transforms

dinitrogen Nitrogen is a chemical element; it has symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh ...

into

at the expense of ATP and reductant—both generated by carbohydrate metabolism, a process supplemented, in the light, by the activity of PS I. Carbohydrate, probably in the form of glucose, is synthesized in vegetative cells and moves into heterocysts. In return, nitrogen fixed in heterocysts moves into the vegetative cells, at least in part in the form of

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

s. The fern '' Azolla'' forms a

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

relationship with the cyanobacterium ''Anabaena azollae'', which fixes

atmospheric An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosphere ...

, giving the plant access to this essential

nutrient A nutrient is a substance used by an organism to survive, grow and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

. This has led to the plant being dubbed a "super-plant", as it can readily colonise areas of freshwater, and grow at great speed - doubling its biomass in as little as 1.9 days. The typical limiting factor on its growth is

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

, abundance of which, due to chemical runoff, often leads to ''Azolla'' blooms. Unlike other known plants, the symbiotic microorganism is transferred directly from one generation to the next. This has made ''Anabaena azollae'' completely dependent on its host, as several of its genes are either lost or have been transferred to the nucleus in Azolla's cells.

Primitive vision pigments studied in ''Anabaena''

''Anabaena'' is used as a

to study simple vision. The process in which light changes the shape of molecules in the

retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

, thereby driving the cellular reactions and signals that cause

vision Vision, Visions, or The Vision may refer to: Perception Optical perception * Visual perception, the sense of sight * Visual system, the physical mechanism of eyesight * Computer vision, a field dealing with how computers can be made to gain und ...

vertebrates Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

, is studied in ''Anabaena''. ''Anabaena'' sensory rhodopsin, a specific light-sensitive membrane protein, is central to this research.

DNA repair

Double strand breaks (DSBs) are a type of DNA damage that can be repaired by

homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in Cell (biology), cellular organi ...

. This enzymatic repair process occurs in several enzymatic steps including an early step catalyzed by RecN protein. A study of the dynamics of RecN in DSB repair in ''Anabaena'' indicated differential regulation of DSB repair so that it is active in vegetative cells but absent in mature heterocysts that are terminal cells.Hu S, Wang J, Wang L, Zhang CC, Chen WL. Dynamics and Cell-Type Specificity of the DNA Double-Strand Break Repair Protein RecN in the Developmental Cyanobacterium Anabaena sp. Strain PCC 7120. PLoS One. 2015 Oct 2;10(10):e0139362. doi: 10.1371/journal.pone.0139362. PMID 26431054; PMCID: PMC4592062

References

External links

* *
Sequenced ''Anabaena'' Genomes
* {{Taxonbar, from=Q133353 Nostocaceae Cyanobacteria genera