Arthrospira platensis

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A Microbial Biorealm page on the genus Arthrospira platensis

Classification

Higher order taxa

Domain: Bacteria

Phylum: Cyanobacteria

Class: Cyanophyceae

Order: Oscillatoriales

Family: Phormidiaceae

Species

Genus: Arthrospira

Species: platensis

Arthrospira (Spirulina) platensis; A. platensis

Description and significance

Arthrospira platensis, also known as Spirulina, is a gram negative, non-toxic species of cyanobacteria with a wide array of uses in the natural and commercial world. While many bacteria are known for their pathogenic effects, A. platensis is primarily known across the world for its potential nutritional value. It is one of the rare edible bacteria due to its low purine concentration, which allows it to pose very minimal risk of uric acid build up in the body(7). Historically, it is known to have been regularly consumed by the Aztecs and tropical climate populations(2). Because of its anti-carcinogen properties, it was also used to treat radiation sickness in people that were affected by the 1986 Chernobyl nuclear accident(5). More recently, the consumption of this species has been shown to lower blood pressure and reduce cholesterol, which are two of the most prevalent health concerns in the modern world(6). The food industry classifies A. platensis as a single-celled protein, meaning that it is an edible microbe with a high food value(8). It is rich in vitamins, minerals, beta-carotene, essential fatty acids, and antioxidants, all of which have facilitated its commercial production as a human food supplement over the course of the past decade(9). It also has very high protein content with a well-balanced composition of all essential amino acids, making it even more desirable as a food supplement(5).

Genome structure

In March 2010, Arthrospira platensis became the first filamentous, non-N2-fixing cyanobacterium to have its genome sequenced and published(2). The genome consists of a single, circular chromosome and was found to be 6.8Mb in size with 44.3% G-C content(2). There were 6630 protein-coding genes detected, as well as 49 RNA genes, including 2 sets of rRNA genes and 40 tRNA genes(2). When looked at in its entirety, 78% of the species' genes showed similarity to genes with known function in other organisms, while 22% of the genome is made up of unknown genes(2).

Cell structure and metabolism

A. platensis is a multicellular, filamentous cyanobacterium. It's cells are spiral-shaped, although in liquid media they take on a helical structure (1). It's vegetative cells contain transverse cross-walls and undergo binary fission on a single plane(3). Under a microscope, A. platensis appears as blue-green unbranched, cylindrical filaments. Although it does not possess any flagella, it has a gliding motility which is still poorly understood (1). Filaments are approximately 5 micrometers in length, and cells are wider than they are long. The cell wall contains 4 layers: an innermost fibril layer, a second peptidoglycan layer, a third layer composed of proteins, and an outermost layer analogous to the cell wall of gram-negative bacteria (1). The cells also contain Na+/H+ antiporters which give them resistance to high salt concentrations(4), and they develop cAMP-dependent signal cascades to adapt to severe environmental conditions(2).

A. platensis is photoautotrophic, obtaining energy from sunlight and converting carbon dioxide and water into sugars. The most important factor that governs A. platensis's growth is the presence of light (3). Its cells contain chlorophylls, carotenoids, and phycobiliproteins, which are pigments that are capable of absorbing light(7). The cytoplasm of A. platensis also contains gas vacuoles, carboxyzomes, and thykaloid membranes as adaptations to being phototrophic. The gas vacuoles within the cells increase their buoyancy so that they remain at the surface of their aqueous environment where the presence of light is greatest. Interestingly, strains of the species grown at suboptimal temperatures have been shown to be more sensitive to photoinhibition than those grown at optimal temperatures(3).

Ecology

A. platensis inhabits tropical and subtropical bodies of water with high pH as well as high levels of carbonate and bicarbonate. It is found mainly in Africa, but also in Asia and South America (3). Aside from being found in naturally in these areas, it is grown commercially for its use as a food additive (6). Conditions for optimal growth of A. platensis include standard mineral nutrient, a temperature range of 30-34 degrees C, pH range of 8.5-11, and a sodium light lamp (5).

Pathology

A. platensis is not pathogenic in nature. On the contrary, it has been shown to potentiate the immune system of its human hosts. It is believed that this microorganism suppresses both cancer development and viral infection (4).

Current Research

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Cool Factor

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References

1. Ciferri O. "Spirulina, the edible microorganism." Microbiol Rev. 47.4 (1983):551-578.

2. Fujisawa, Takatomo et al. “Genomic Structure of an Economically Important Cyanobacterium, Arthrospira (Spirulina) platensis NEIS-39.” DNA Research 17 (2010): 85-103.

3. Gao, Kunshan, Ma, Zengling. “Photosynthesis and growth of Artropira (Spirulina) platensis (Cyanophyta) in response to solar UV radiation, with special reference to its minor variant.” Environmental and Experimental Botony 63.1-3 (2007): 123-129.

4. Hirahashi, Tomohiro et al. “Activation of the human innate immune system by Spirulina: augmentation of interferon production and NK cytotoxicity by oral adminstration of hot water extract of Spirulina platensis.” International Immunopharmacology 2.4 (2002): 423-434

5. Mosulishvili, L. M., E. I. Kirkesali, A. I. Beiokobylsky, and A. I. Khizanishvili. “Experimental Substantion of the Possibility of Developing Selenium and Iodine Containing Pharmaceuticals Based on Blue-green Algae Spirulina platensis.” Journal of Pharmaceutical and Biomedical Analysis 30.1 (2002): 87-97. Web. 5 Oct. 2011.

6. National Center for Biotechnology Information. Web. 05 Oct 2011. <http://www.ncbi.nlm.nih.gov/bioproject?Db=genome&Cmd=ShowDetailView&TermToSearch=6605.>

7. Singh, Nirbhay Kumar and Dolly Wattal Dhar. “Phylogenetic Relatedness Among Spirulina and Related Cyanobacterial Genera.” World J Microbiol Biotechnol 27 (2011): 941-951.

8. Slonczewski, Joan L. and John W. Foster. Microbiology: An Evolving Science. 2nd Ed. New York: W. W. Norton & Company, Inc., 2009. 141-685.

9. Watunuki, Hironubu, Kazuki Ota, Asmi Citra Malina, A. R. Tassakka, Toshimitsu Kato, and Masahiro Sakai. “Immunostimulant Effects of Dietary Spirulina platensis on Carp, Cyprinus Carpio.” Aquaculture 258. 1-4 (2006): 157-63. Web. 5 Oct. 2011.

Edited by student of Iris Keren NEUF2011