In its commercial use, the common name, Spirulina, refers to the dried biomass of the cyanobacterium, Arthrospira platensis, and is a whole product of biological origin. The source strain, cultivated by producers in the United States was obtained from the University of Texas at Austin Algae Culture Collection (UTEX). This strain, designated UTEX 1926, was originally isolated from an alkaline salt flat near Del Mar, California, by R. Lewin in 1969.
In its taxonomic use, Spirulina is a name used to describe mainly two species of Cyanobacteria, A. platensis and A. maxima, that are commonly used as food, dietary supplement, and feed supplement. These and other Arthrospira species were once classified by Geitler1 who combined all species forming helical trichomes into a single genus, Spirulina. Before Geitler, Gomont2 had in fact placed the two genera as separate on the basis of the presence of septa or divisions in the trichomes, the Spirulina species being without septa and the Arthrospira species with septa. Recent detailed studies of morphological, physiological, and biochemical examination of representatives of these genera have shown that these two genera are distinctively different and that the edible forms commonly referred to as Spirulina platensis have little in common with other much smaller species such as Spirulina major.3-5 This distinction has also been borne out by results from the complete sequence of the 16S rRNA gene and the internal transcribed spacer (ITS) between the 16S and 23S rRNA genes determined for two Arthrospira strains and one Spirulina strain showing that the two Arthrospira strains formed a close cluster distant from the Spirulina strain.6
The various Arthrospira species found in nature and in culture collection appear to be very closely related. Scheldeman et al.7 carried out an ARDRA (Amplified
Ribosomal DNA Restriction Analysis on the ITS of 37 cultivated clonal strains from four continents. The data showed that all these strains were closely related. Only two different major restriction patterns were discernible defining two clusters, I and II, with two strains from cluster I falling in a small subcluster. No clear relationship could be observed between this division into two clusters and the geographic origin of the strains, their designation in the culture collection, or their morphology. Subsequent studies by Baurain et al.,8 using amplification and determination of the full ITS, also showed a remarkable conservation of the ITS sequences of 21 of the 37 Arthrospira clonal strains from the four continents and assigned to four different species (A. platensis, A. maxima, A. fusiformis, A. indica) in the culture collections. Using 28 morphological characters or character states, Muhling et al.9 have also found these strains to be grouped into two loose clusters. It is therefore evident that these strains are very closely related and the assignment of binomial is therefore difficult at this stage of our knowledge of their taxonomy.
It should be pointed out that the name Spirulina is used commonly as a name of commerce and will continue to be used since many companies have devoted a lot of money in the marketing of Arthrospira with the trade name of Spirulina. This chapter will use these names interchangeably with the understanding that all the edible forms that are under commercial cultivation and sold as "Spirulina" actually belong to the Genus Arthrospira.
The botanical nomenclature is also used often because Spirulina and Arthrospira are considered plants (blue-green algae) by botanists who look at the photosynthetic ability of these organisms as a major determinant of their classification. However, the most recent comprehensive treatise on the subject identifies Arthrospira as follows10:
Phylum BX. Cyanobacteria
Subsection III. (formerly Order Oscillatoriales)
Form-genus I. Arthrospira
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