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Anabaena

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For Anabaena A.Juss., a plant genus of the Euphorbiaceae, see its synonym Romanoa.

Anabaena
Anabaena sphaerica
Scientific classification Edit this classification
Domain: Bacteria
Kingdom: Bacillati
Clade: "Cyanobacteria/Melainabacteria clade"
Phylum: Cyanobacteria
Class: Cyanophyceae
Order: Nostocales
Family: Nostocaceae
Genus: Anabaena
Bory de Saint-Vincent ex Bornet & Flahault, 1886[1]
Species

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Anabaena is a genus of filamentous cyanobacteria that exist as plankton. They are known for nitrogen-fixing abilities, and they form symbiotic relationships with certain plants, such as the mosquito fern. They are one of four genera of cyanobacteria that produce neurotoxins, 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 project was undertaken by the United States Department of Energy between 1999 and 2005. This project mapped the complete genome of model organism Anabaena variabilis ATCC 29413, which is 7.2 million base pairs long.[2][3] A paper detailing the process was published in 2014.[4] The study focused on heterocysts, which convert nitrogen into ammonia. Certain species of Anabaena have been used on rice paddy fields, proving to be an effective natural fertilizer.

Species

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List of current (C), unverified (U), and preliminary (P) species from AlgaeBase:[5]

List of synonimized species from AlgaeBase:[5]

Recent changes

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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.[6] 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.[7]

  • In 2009, a 42-species group under the "planktic" main-group, determined by 16S rRNA or gas vesicle morphotype, were transferred to Dolichospermum.[8]
  • 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.

Nitrogen fixation by Anabaena

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Anabaena sp.

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 ammonia 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.[9]

The fern Azolla forms a symbiotic relationship with the cyanobacterium Anabaena azollae, which fixes atmospheric nitrogen, giving the plant access to this essential nutrient. 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.[10] 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 have been transferred to the nucleus in Azolla's cells.[11]

Primitive vision pigments studied in Anabaena

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Anabaena is used as a model organism 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.[12]

DNA repair

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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.[13] 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.[14]

References

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  1. ^ Anabaena Bory de Saint-Vincent ex Bornet & Flahault, 1886: 180, 224
  2. ^ "Home - Anabaena variabilis ATCC 29413". genome.jgi.doe.gov.
  3. ^ "Anabaena variabilis ATCC 29413, complete genome". 28 January 2014.
  4. ^ Thiel, T; Pratte, BS; Zhong, J; Goodwin, L; Copeland, A; Lucas, S; Han, C; Pitluck, S; Land, ML; Kyrpides, NC; Woyke, T (15 June 2014). "Complete genome sequence of Anabaena variabilis ATCC 29413". Standards in Genomic Sciences. 9 (3): 562–73. Bibcode:2014SGenS...9..562T. doi:10.4056/sigs.3899418. PMC 4148955. PMID 25197444.
  5. ^ a b "Anabaena Bory ex Bornet & Flahault, 1886, nom. cons. :: AlgaeBase". www.algaebase.org.
  6. ^ Rajaniemi, Pirjo; Hrouzek, Pavel; Kaštovská, Klára; Willame, Raphaël; Rantala, Anne; Hoffmann, Lucien; Komárek, Jiří; Sivonen, Kaarina (1 January 2005). "Phylogenetic and morphological evaluation of the genera Anabaena, Aphanizomenon, Trichormus and Nostoc (Nostocales, Cyanobacteria)". International Journal of Systematic and Evolutionary Microbiology. 55 (1): 11–26. doi:10.1099/ijs.0.63276-0. PMID 15653847.
  7. ^ Rajaniemi, Pirjo; Komárek, Jiří; Willame, Raphaël; Hrouzek, Pavel; Kaštovská, Klára; Hoffmann, Lucien; Sivonen, Kaarina (1 October 2005). "Taxonomic consequences from the combined molecular and phenotype evaluation of selected Anabaena and Aphanizomenon strains". Algological Studies/Archiv für Hydrobiologie, Supplement Volumes. 117: 371–391. doi:10.1127/1864-1318/2005/0117-0371. {{cite journal}}: C1 control character in |last5= at position 3 (help)
  8. ^ Wacklin, Pirjo; Hoffmann, Lucien; Komárek, Jiří (1 March 2009). "Nomenclatural validation of the genetically revised cyanobacterial genus Dolichospermum (RALFS ex BORNET et FLAHAULT) comb. nova". Fottea. 9 (1): 59–64. Bibcode:2009Fotte...9...59W. doi:10.5507/fot.2009.005.
  9. ^ Herrero, Antonia; Flores, Enrique, eds. (2008). The Cyanobacteria: Molecular Biology, Genomics and Evolution (1st ed.). Caister Academic Press. ISBN 978-1-904455-15-8.[page needed]
  10. ^ Iwao Watanabe, Nilda S.Berja (1983). "The growth of four species of Azolla as affected by temperature". Aquatic Botany. 15 (2): 175–185. Bibcode:1983AqBot..15..175W. doi:10.1016/0304-3770(83)90027-X.
  11. ^ The Arctic Azolla event - The Geological Society
  12. ^ Schapiro, Igor (May 2014). "Ultrafast photochemistry of Anabaena Sensory Rhodopsin: Experiment and theory". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1837 (5): 589–597. doi:10.1016/j.bbabio.2013.09.014. PMID 24099700.
  13. ^ "InterPro". www.ebi.ac.uk. Retrieved 18 November 2023.
  14. ^ 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

Further reading

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