Bacteria Genomes - NOSTOC

Anabaena sp. PCC 7120 (synonym Nostoc SP Pcc 7120) is a filamentous, heterocyst-forming cyanobacterium capable of nitrogen fixation.

These cyanobacteria are photosynthetic prokaryotes that carry out an oxygen-evolving photosynthesis virtually identical to that of higher plants. Some cyanobacteria are also capable of nitrogen fixation. Because the enzyme that performs nitrogen fixation is extremely sensitive to oxygen, nitrogen fixation must occur in an anaerobic environment, this creates a special problem for cyanobacteria since oxygen is generated as a by-product of photosynthesis and yet photosynthesis is required to produce the energy for nitrogen fixation.

Certain filamentous cyanobacteria such as Anabaena deal with this problem by physically separating the functions of nitrogen fixation and photosynthesis. Nitrogen starvation of Anabaena induces certain vegetative cells along the filament to develop into specialised cells called heterocysts. Heterocysts are the exclusive sites of nitrogen fixation within the filament and carry out an incomplete photosynthesis relative to neighbouring vegetative cells.

Some species of Anabaena , which can be found worldwide, have been successfully used to provide nitrogen to rice crops in flooded paddy fields. By increasing the nitrogen content of the soil, cyanobacteria provide an important source of natural fertilizer.

References:

http://www.cals.ncsu.edu/genetics/curtis/curtis.html
http://www-cyanosite.bio.purdue.edu/
DNA Res. 8 (5):205-13; 227-53 (2001)