The genus Arthrospira Stizenberger includes filamentous Oscillatoriaceae with multicellular cylindrical trichomes arranged in an helicoidal shape, with cross-walls visible by light microscopy, and containing gas-vesicles. The trichomes are motile and their diameters vary generally from 5 to 12 µm. Cells are generally shorter than broad or isodiametric (Castenholz et al., 2001).

Many strains are industrially cultivated as a health food due to their richness in proteins, essential fatty acids (linoleic and gamma-linoleic acid), vitamins (provitamin A, vitamin B12, ...) and minerals (iron source), and are currently commercialised under the name "Spirulina". The confusion between both names has arisen due to Geitler's decision to unite the two genera Arthrospira Stizenberger and Spirulina Turpin in his Flora in 1932, on the basis of their coiled trichomes (Geitler, 1932). However, the true Spirulina are not related to Arthrospira (Nelissen et al., 1994).
Organisms of the Arthrospira genus are commonly found in marine, brackish water and saline lake environments of tropical and semi-tropical regions (Castenholz et al., 2001). The precise origin of Arthrospira sp. PCC 8005 is unknown. It belonged to a set of 4 strains from India, Kenya, Mexico and Peru deposited in the Pasteur Collection of Cyanobacteria (PCC) by Dr. Jeeji-Bai in 1980, but the notebook with the information was lost by a student (R. Rippka, personal communication). However, its ITS sequence is identical to the one of another indian strain (A. indica MCRC straight) given later by Dr. Jeeji-Bai to Scheldeman et al. (1999).
Arthrospira was consumed by the Aztecs in the sixteenth century, and is presently still a source of proteins for the Kanembu tribe in Chad. It is harvested in small wadi by women, dried, and sold as " dihé " at the market place.
It is well known that cyanobacteria have played a major role in the evolution of life on Earth. In particular, they are thought to be the main cause of the oxygenation of our atmosphere. Nowadays, they still make a significant contribution to the global oxygen production in the oceans (Garcia-Pichel, 2000). They even became locally dominant primary producers of oxygen, carbon and organics in extreme environments such as hot and cold deserts, hot springs and hypersaline environments (Garcia-Pichel, 2000). Because of these particular characteristics, Arthrospira was selected as a complementary food source and for the production of oxygen in the Life-Support system MELiSSA (Micro-Ecological Life Support System) that is constructed for long-term spatial missions.

References:

• CASTENHOLZ, RW, RIPPKA, R, HERDMAN, M & WILMOTTE, A. (2001) Form-genus I. Arthrospira Stizenberger 1852. In: Bergey's Manual of Systematic Bacteriology, Vol. 1 (D. R. Boone & R.W. Castenholz, eds.). Springer, NewYork, USA , pp 542-543.
• GARCIA-PICHEL, F. (2000). Cyanobacteria. In: Encyclopedia of Microbiology, Vol. 1. A. Press, pp 907-929.
• GEITLER, L.(1932) Cyanophyceae. In: Rabenhorst's Kryptogamenflora von Deutschland, Österreich und der Schweiz, Leipzig, Akad. Verslagsges. 1932. Reprinted 1971, New York, Johnson, pp. 1-1196.
• NELISSEN, B., WILMOTTE, A., NEEFS, J.M. & DE WACHTER, R. (1994) Phylogenetic relationships among filamentous helical cyanobacteria investigated on the basis of 16S ribosomal RNA gene sequence analysis. In: Systematic and Applied Microbiology, vol 17, pp 206-210.
• SCHELDEMAN, P., BAURAIN, D., BOUHY, R., SCOTT, M., MUHLING, M., WHITTON, B.A., BELAY, A.& WILMOTTE, A. (1999) Arthrospira ("Spirulina") strains from four continents are resolved into only two clusters, based on amplified ribosomal DNA restriction analysis of the internally transcribed spacer. In: FEMS Microbiology Letters 172: 213-222.