Arthrospira is a genus of free-floating filamentous cyanobacteria characterized by cylindrical, multicellular trichomes in an open left-hand helix. There is a dietary supplement made from Arthrospira platensis and Arthrospira maxima, known as Spirulina. The maxima and platensis species were once classified in the genus Spirulina. ″Although the introduction of two separate genera [Arthrospira and Spirulina] is now generally accepted, there has been much dispute in the past and the resulting taxonomical confusion is tremendous″. ″
The maxima and platensis species were once classified in the genus Spirulina. The common name, Spirulina, refers to the dried biomass of Arthrospira platensis, which belongs to the oxygenic photosynthetic bacteria that cover the groups Cyanobacteria and Prochlorales. These photosynthetic organisms, Cyanobacteria, were first considered as alge until 1962 and for the first time, these blue green algae were added to prokaryote kingdom and proposed to call these microorganisms as Cyanobacteria  where algae is considered to be a very large and diverse group of eukaryotic organisms. This designation was accepted and published in 1974 by the Bergey's Manual of Determinative Bacteriology. Scientifically, there is a quite distinction between Spirulina and Arthrospira genus. Stizenberger, in 1852 gave the name Arthrospira based on the septa presence, helical form and multicellular structure and Gomont in 1892, confirmed aseptate form of the Spirulina genus. Geitler in 1932, reunified both members designating them as Spirulina without considering the septum. The worldwide research on microalgae was carried out in the name of Spirulina, but the original species exploited as food with excellent health properties belongs to genus Arthrospira. This common difference between scientists and customers is difficult to change. These Arthrospira genus, constitute a helical trichomes of varying size and with various degree of coiling including tightly coiled morphology to even straight uncoiled form. The filaments are solitary and reproduce by binary fission and the cells of the trichomes vary from 2 μm to 12 μm and can sometime reach up to 16 μm. Species of the genus Arthrospira have been isolated from alkaline brackish and saline waters in tropical and subtropical regions. Among the various species included in the genus Arthrospira, A. platensis is the most widely distributed and is mainly found in Africa but also in Asia. Arthrospira maxima is believed to be found in California and Mexico. They are now agreed to be in fact Arthrospira; nevertheless, and somewhat confusingly, the older term Spirulina remains in use for historical reasons. However, current taxonomy claims that the name ′Spirulina′ for strains used as food supplements is inappropriate, and there is agreement that Arthrospira is a distinct genus, consisting of over 30 different species including A. platensis and A. maxima″.
Arthrospira platensis and Arthrospira maxima occur naturally in tropical and subtropical lakes with high pH and high concentrations of carbonate and bicarbonate. Arthrospira platensis occurs in Africa, Asia and South America, whereas Arthrospira maxima is confined to Central America and Arthrospira pacifica is endemic to Hawaii Islands of America. Most cultivated spirulina is produced in open channel raceway ponds, with paddle-wheels used to agitate the water. The largest commercial producers of spirulina are located in the United States, Thailand, India, Taiwan, China, Pakistan, Burma (a.k.a. Myanmar), Greece and Chile.
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