Spirulina sp. have gained worldwide fame as a health food. One can purchase dried Spirulina sp. biomass ("super blue-green algae") to supplement one's diet. Proponents of this supplement claim that eating cyanobacteria gives one enhanced vigor and energy. Cyanobacteria have been eaten for centuries in cultures around the world. In Mexico, it was called "excrement of the stones" since it grew on rocks in nearby lakes. The material was gathered and sun-dried to give a foodstuff with the consistency of butter that was smeared on breads. Cyanobacteria are still grown and consumed by peoples living around Lake Chad in Africa. It is true that cyanobacteria, like all bacteria, are rich sources of protein. Approximately 50% of the weight of a bacterium is protein and its amino acid composition is well-balanced for human nutrition. Cyanobacteria tend to be very low in fats (less than 1%) and what fats they have are often enriched in the essential fatty acids linoleic and linolenic acids. Cyanobacteria often produce Vitamin B12 which cannot be obtained from plant sources and can provide bioavailable dietary metals. The problem with eating large quantities of cyanobacteria is the relatively high nucleic acid content of bacteria. This leads to the accumulation of purine bases in the blood and can cause symptoms similar to gout. Cyanobacteria may be a safe and useful dietary supplement, but adult intake should never exceed a few grams per day.
The Spirulina is grown commercially in large outdoor ponds. These can have a racetrack configuration and must be aerated in some way. If properly maintained, the ponds tend to only grow Spirulina and not other microbes, even though they are open to the environment. The reason for this is that Spirulina grow at a very high pH, over 10, and they maintain this high pH. Most organisms cannot live at this pH. The Spirulina will often form floating mats on the surface of the ponds. The Spirulina are harvested using screen mesh in which the filamentous Spirulina get caught. The biomass can be sun-dried or dried in rotating heated drums.
This specimen of Spirulina major came from a fish hatchery pond on the University of Arkansas at Pine Bluff campus. It is very common in this location. The organism was not isolated, but photographed from the natural water sample, using a light microscope and 400x magnification. Note the spiral shape of the cell that led to the genus name Spirulina.
References on cyanobacteria as foodstuffs:
1. Becker, E. W. 1988. Micro-algae for human and animal consumption, p. 222-256. In M. A. Borowitzka and L. J. Borowitzka (ed.), Micro-algal Biotechnology. University Press, Cambridge.
2. Becker, E. W., and L. V. Venkataraman. 1984. Production and utilization of the blue-green alga Spirulina in India. Biomass 4:105-125.
3. Contreras, A., D. C. Herbert, B. G. Grubbs, and I. L. Cameron. 1979. Blue-green alga, Spirulina, as the sole dietary source of protein in sexually maturing rats. Nutrition Reports International 19:749-763.
4. Schneegurt, M. A., B. Arieli, J. D. McKeehan, S. D. Stevens, S. S. Nielsen, P. R. Saha, P. R. Trumbo, and L. A. Sherman. 1995. Compositional and toxicological evaluation of the diazotrophic cyanobacterium, Cyanothece sp. strain ATCC 51142. Aquaculture 134:339-349.