''Anabaena'' is a genus of filamentous cyanobacteria that exist as plankton. They are known for nitrogen-fixing abilities, and they form

symbiotic 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 ...

relationships with certain plants, such as the mosquito fern. They are one of four genera of cyanobacteria that produce

neurotoxin Neurotoxins are toxins that are destructive to nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insultsSpencer 2000 that can adversely affect function in both developing and mature ner ...

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 pressure. A DNA

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 in 1999, which mapped the complete genome of ''Anabaena'', which is 7.2 million base pairs long. The study focused on heterocysts, which convert nitrogen into ammonia. Certain species of ''Anabaena'' have been used on rice

paddy field A paddy field is a flooded field (agriculture), field of arable land used for growing Aquatic plant, semiaquatic crops, most notably rice and taro. It originates from the Neolithic rice-farming cultures of the Yangtze River basin in sout ...

s, proving to be an effective natural fertilizer.

Nitrogen fixation by ''Anabaena''

Under nitrogen-limiting conditions, vegetative cells differentiate into heterocysts 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 into

ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...

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 acids. The fern '' Azolla'', forms a

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

atmospheric An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

nitrogen, 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, 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 has been transferred to the nucleus in Azolla's cells.

Primitive vision pigments studied in ''Anabaena''

''Anabaena'' is used as a

model organism A model organism (often shortened to model) 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 workin ...

to study simple vision. The process in which light changes the shape of molecules in the retina, thereby driving the cellular reactions and signals that cause vision in vertebrates, 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. 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

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

Nitrogen fixation by ''Anabaena''

Primitive vision pigments studied in ''Anabaena''

DNA repair

References

Further reading

External links