Anabaena

Anabaena is a genus of filamentous cyanobacteria. Many species fix atmospheric nitrogen in specialized cells called heterocysts.

Heterocyst: A specialized cyanobacterial cell that fixes nitrogen while limiting oxygen exposure to its nitrogenase enzymes. Many Anabaena filaments differentiate these cells when fixed nitrogen is scarce.
Cyanobacteria: A diverse group of bacteria that perform oxygen-producing photosynthesis. Anabaena belongs to this group of photosynthetic bacteria.
Azolla–Anabaena symbiosis: A partnership in which nitrogen-fixing cyanobacteria live within the water fern Azolla. This association makes Anabaena a source of nitrogen in rice-field systems.
Nostoc: A genus of filamentous, nitrogen-fixing cyanobacteria that can form gelatinous colonies. Nostoc shares heterocysts with Anabaena but differs in its typical colony forms and classification.
Nitrogen fixation: The biological conversion of atmospheric nitrogen gas into ammonia or related compounds organisms can use. This process supplies usable nitrogen to many Anabaena species.
Prokaryote: An organism whose cells lack a membrane-bound nucleus. Anabaena’s cells have bacterial organization rather than a nucleus.
Azolla: A genus of small floating aquatic ferns that host nitrogen-fixing cyanobacteria. Azolla provides a plant partner for Anabaena in a widely used agricultural association.
Oscillatoria: A genus of filamentous cyanobacteria known for gliding movement and generally lacking heterocysts. Its filaments illustrate a cyanobacterial lifestyle without Anabaena’s nitrogen-fixing cell specialization.
Nitrogenase: An oxygen-sensitive enzyme complex that catalyzes biological nitrogen fixation. Heterocysts protect this enzyme complex so Anabaena can fix nitrogen.
Vegetative cell: A growing, non-reproductive cell that carries out an organism’s ordinary metabolism. These cells make up most Anabaena filaments and perform oxygen-producing photosynthesis.

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