Arthrospira is a genus of free-floating filamentous cyanobacteria characterized by cylindrical, multicellular trichomes in an open left-hand helix. A dietary supplement is made from A. platensis and A. maxima, known as spirulina. The A. maxima and A. platensis species were once classified in the genus Spirulina. Although the introduction of the 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.
Taxonomy
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 were first considered to be algae, a very large and diverse group of eukaryotic organisms, until 1962 when they were reclassified as prokaryotes and named Cyanobacteria. This designation was accepted and published in 1974 by Bergey's Manual of Determinative Bacteriology. Scientifically, quite a distinction exists between the Spirulina and Arthrospira genera. Stizenberger, in 1852, gave the name Arthrospira based on the presence of septa, its helical form, and its multicellular structure, and Gomont, in 1892, confirmed the aseptate form of the genus Spirulina. Geitler in 1932 reunified both members designating them as Spirulina without considering the septum. Research on microalgae was carried out in the name of Spirulina, but the original species used to produce the dietary supplement spirulina belongs to the genus Arthrospira. This misnomer has been difficult to correct. At present, taxonomy states that the name spirulina for strains which are used as food supplements is inappropriate, and agreement exists that Arthrospira is a distinct genus, consisting of over 30 different species, including A. platensis and A. maxima.
Morphology
The genus Arthrospira comprises helical trichomes of varying size and with various degrees of coiling, including tightly-coiled morphology to a straight form.
The helical parameters of the shape of Arthrospira is used to differentiate between and even within the same species. These differences may be induced by changing environmental conditions, such as temperature. The helical shape of the trichomes is only maintained in a liquid environment. The filaments are solitary and reproduce by binary fission, and the cells of the trichomes vary in length from 2 to 12 μm and can sometimes reach 16 μm.
Biochemical composition
Arthrospira is very rich in proteins, and constitute 53 to 68 percent by dry weight of the contents of the cell. Its protein harbours all essential amino acids. Arthrospira also contain high amounts of polyunsaturated fatty acids (PUFAs), about 1.5–2 percent, and a total lipid content of 5–6 percent. These PUFAs contain the γ-linolenic acid (GLA), an omega-6 fatty acid. Further contents of Arthrospira include vitamins, minerals and photosynthetic pigments.
Occurrence
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, A. platensis is the most widely distributed and is mainly found in Africa, but also in Asia. A. maxima is believed to be found in California and Mexico. A. platensis and A. maxima occur naturally in tropical and subtropical lakes with alkaline pH and high concentrations of carbonate and bicarbonate. A. platensis occurs in Africa, Asia and South America, whereas A. maxima is confined to Central America. A. pacifica is endemic to the Hawaiian islands. 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, Myanmar, Greece and Chile.