Anabaena


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



Anabaena is a genus of filamentous cyanobacteria, or blue-green algae, found as plankton. It is known for its 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.

A DNA sequencing project was undertaken in 1999, which mapped the complete genome of Anabaena, which is 7.2 million base pairs long. The study focussed 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

 * Anabaena aequalis
 * Anabaena affinis
 * Anabaena angstumalis
 * Anabaena angstumalis angstumalis
 * Anabaena angstumalis marchica
 * Anabaena aphanizomendoides
 * Anabaena azollae
 * Anabaena bornetiana
 * Anabaena catenula
 * Anabaena circinalis
 * Anabaena confervoides
 * Anabaena constricta
 * Anabaena cycadeae
 * Anabaena cylindrica
 * Anabaena echinispora
 * Anabaena felisii
 * Anabaena flosaquae
 * Anabaena flosaquae flosaquae
 * Anabaena flosaquae minor
 * Anabaena flosaquae treleasei
 * Anabaena helicoidea
 * Anabaena inaequalis
 * Anabaena lapponica
 * Anabaena laxa
 * Anabaena lemmermannii
 * Anabaena levanderi
 * Anabaena limnetica
 * Anabaena macrospora
 * Anabaena macrospora macrospora
 * Anabaena macrospora robusta
 * Anabaena monticulosa
 * Anabaena oscillarioides
 * Anabaena planctonica
 * Anabaena raciborskii
 * Anabaena scheremetievi
 * Anabaena sphaerica
 * Anabaena spiroides
 * Anabaena spiroides crassa
 * Anabaena spiroides spiroides
 * Anabaena subcylindrica
 * Anabaena torulosa
 * Anabaena unispora
 * Anabaena variabilis
 * Anabaena verrucosa
 * Anabaena viguieri
 * Anabaena wisconsinense
 * Anabaena zierlingii

Nitrogen Fixation by Anabaena
Under nitrogen-limiting conditions, vegetative cells differentiate into heterocysts at semi-regular intervals along the filaments. Heterocysts are cells that are terminally specialized for nitrogen fixation. The interior of these cells is microoxic 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 at the expense of ATP and reductant—both generated by carbohydrate metabolism, a process that is supplemented, in the light, by the activity of PS I. Carbohydrate, probably in the form of sucrose, 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.