Spirulina are multicellular ilamentous cyanobacteria actually belonging to two separate genera: Spirulina and Arthrospira. These encompass about 15 species (Habib et al., 2008). This microorganism grows in water, reproduces by binary fission, and can be harvested and processed easily, having significantly high macro — and micronutrient contents. Their main photosynthetic pigments are chlorophyll and phycocyanin. The helical shape of the filaments (or trichomes) is characteristic of the genus and is maintained only in a liquid environment or culture medium.

Spirulina is found in soil, marshes, freshwater, brackish water, seawater, and thermal springs. Alkaline, saline water (>30 g/L) with high pH (8.5-11.0) favors good production of Spirulina, especially where there is a high level of solar radiation. It predominates in higher pH and water conductivity. Like most cyanobacteria, Spirulina is an obligate photoautotroph,

i. e., it cannot grow in the dark on media containing only organic carbon compounds. It reduces carbon dioxide in the light and assimilates mainly nitrates.

Spirulina contains unusually high amounts of protein, between 55% and 70% by dry weight, depending on the source. It has a high amount of polyunsaturated fatty acids (PUFAs), 30% of its 5-6% total lipids, and is a good source of vitamins (B1, B2, B3, B6, B9, B12, C, D, E). Spirulina is a rich source of potassium and also contains calcium, chromium, copper, iron, magnesium, manganese, phosphorus, selenium, sodium, and zinc. These bacteria also contain chlorophyll a and carotenoids.

The optimum pH of the Spirulina sp. culture is between 8.5 and 9.5 (Watanabe et al., 1995). Cyanobacteria possess a CO2-concentating mechanism that involves active CO2 uptake and HCO — transport. In experiments conducted by Morais and Costa (2007), carbon fixation in terms of biomass by Spirulina platensis was estimated in 413 mg L-1 d-1, near those achieved by Sydney et al. (2011).