Limnospira 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 L. platensis and L. maxima, known as spirulina. It was split from Arthrospira in 2019. The two species were commonly treated as if they are in the genus Spirulina since 1932, even though they were originally proposed in Arthorospira in 1892 and 1917. The distinction was restored in the late 20th century. 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. To add to the problem, it was shown in 2019 that the type species for Arthrospira, A. jenneri, was very distantly related to the species used in food production. This necessitated the creation of yet another genus, Limnospira, to hold these economically-important species.
Taxonomy The common name, spirulina, refers to the dried biomass of Arthrospira platensis (now L. platensis), a type of Cyanobacteria, which are oxygenic (produce oxygen) photosynthetic bacteria. 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. As of 2010, 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. A 2019 analysis of Arthrospira species using 16S rRNA gene sequence suggests that the type species of this genus (A. jenneri) is much closer to Planktothrix clade than previously thought. It also lacks characteristics of mass produced species (such as preference of alkaline habitats). As a result, researchers proposed a new genus closer to Limnoraphis and Neolyngbya called Limnospira comprising L. fusiformis, L. maxima and L. indica. A further 2024 study confirmed that L. platensis should be in this genus, but also found that L. fusiformis and L. indica are insufficiently different from L. maxima to be their own species.
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
Limnospira 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. Limnospira 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 Limnospira include vitamins, minerals and photosynthetic pigments.
Occurrence Species of the genera Limnospira have been isolated from alkaline brackish and saline waters in tropical and subtropical regions. Among the various species included in the genus, L. platensis is the most widely distributed and is mainly found in Africa, but also in Asia. L. maxima is believed to be found in California and Mexico. L. platensis and L. maxima occur naturally in tropical and subtropical lakes with alkaline pH and high concentrations of carbonate and bicarbonate. L. platensis occurs in Africa, Asia and South America, whereas L. maxima is confined to Central 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, Myanmar, Greece and Chile. An invalid name "Arthrospira pacifica" has been used to describe an algae found in Hawaii, also used for "spirulina" production through cultivation in raceway ponds. Although no sequence data is available, its use suggests that it is likely some form of Limnospira.
Present and future uses Spirulina is widely known as a food supplement, but there are other possible uses for this cyanobacterium. As an example, it is suggested to be used medically for patients for whom it is difficult to chew or swallow food, or as a natural and cheap drug delivery system. Further, promising results in the treatment of certain cancers, allergies and anemia, as well as hepatotoxicity and vascular diseases were found. Spirulina may also be used as a healthy addition to animal feed if the price of its production can be further reduced Spirulina can be used in technical applications, such as the biosynthesis of silver nanoparticles, which allows the formation of metallic silver in an environmentally friendly way. In the creation of textiles it harbors some advantages, since it can be used for the production of antimicrobial textiles and paper or polymer materials. They also may have an antioxidant effect and may maintain the ecological balance in aquatic bodies and reduces various stresses in the aquatic environment.
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