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, Arthrospira 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(5). Historically, it is known to have been regularly consumed by the Aztecs and tropical climate populations(1). 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(2). 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(3). The food industry classifies Arthrospira platensis as a single-celled protein, meaning that it is an edible microbe with a high food value(5). 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(6). 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(2).

Genome structure

In March 2010, Arthrospira platensis became the first filamentous, non-N2-fixing cyanobacterium to have its genome sequenced and published(1). The genome consists of a single, circular chromosome and was found to be 6.8Mb in size with 44.3% G-C content(1). There were 6630 protein-coding genes detected, as well as 49 RNA genes, including 2 sets of rRNA genes and 40 tRNA genes(1). 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(1).

Cell structure and metabolism

Arthrospira platensis is a multicellular, filamentous cyanobacterium. It's cells are spiral-shaped, although in liquid media they take on a helical structure. It's vegetative cells contain transverse cross-walls and undergo binary fission on a single plane. 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. Filaments are approximately 5 micrometers, and cells are wider than they are long. The cytoplasm of A. platensis contains gas vacuoles, carboxyzomes, and thykaloid membranes. 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. The cells contain Na+/H+ antiporters which give them resistance to high salt concentrations, and they develop cAMP-dependent signal cascades to adapt to severe environmental conditions.

A. platensis is photoautotrophic, obtaining energy from sunlight and converting carbon dioxide and water into sugars. Its cells contain chlorophylls, carotenoids, and phycobiliproteins, pigments that are used to absorb light. The most important factor that governs A. platensis's growth is the presence of light. Also, those grown at suboptimal temperatures have been shown to be more sensitive to photoinhibition than those grown at optimal temperatures.

Ecology

Habitat; symbiosis; contributions to the environment.

Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

Current Research

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Cool Factor

Describe something you fing "cool" about this microbe.

References

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

2. 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.

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

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

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

6. 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