Definition, history and properties

A high-value nutritional and therapeutic dietary supplement

Spirulina (Arthrospira platensis) is a micro-organism, which grows rapidly in photosynthesis. It is referred to as a ‘cyanobacterium’, for which the approximate term ‘blue-green alga’ is often used as a synonym, though not entirely accurately. Whilst the latter term was applied in the past to spirulina, and is hard for some to shake off, the organism is not properly speaking an alga. It grows naturally in the alkaline water of certain lakes, in warm, brackish waters.

It is typically 0.1 millimetre in length, looking like a miniscule green filament rolled into a great many closely-bound spirals.

Spirulina has been eaten in some communities in Chad for centuries and to this day. Nowadays it is used principally as a dietary supplement of great nutritional and therapeutic value. It is very rich in micronutrients which are easily absorbed by the human body, including beta-carotene (the basis for vitamin A), iron, vitamin B12, gamma-linolenic acid (GLA) and essential fatty acids. These micronutrients enable the body to grow properly and to maintain its vital functions.

Antenna has sequenced the spirulina genome

The spirulina genome was sequenced entirely in July 2009, by Antenna Technologies and two private Swiss companies – Biorigin SA and Fasteris – as well as the Haute École Spécialisée Hepia in Geneva, represented by its research group for Plants and Pathogens.

These parties registered the spirulina genome in the GenBank, thus making it publicly and freely accessible to all potential users and preventing any attempt to patent it. Any interested party can thereby make faster and greater progress in the many potential uses of the organism. These can include nutritional applications, in industrial ecology through carbon sequestration and, indeed, in the production of molecules for therapeutic ends. The complete sequencing of the spirulina genome also enables our own researchers in Antenna to respond to a concern occasionally voiced by certain biologists, namely, given the ability of many cyanobacteria, under certain circumstances, to produce powerful toxins, on where things stand on this front with spirulina.

A cyanobacterial foodstuff

Cyanobacteria are the prime bacteria capable of photosynthesis to produce oxygen. They can be either unicellular or multicellular. In the latter case, the cells accumulate in colony-type piles, typically in threads of aligned cells. These filaments are called ‘trichomes’.

They are thus real prokaryotes, organisms with no nuclear membrane. This is despite their photosynthetic system being close to that of eukaryotes which contain chlorophyll-a and a II photosystem (PS-II).

This photosystem, together with photosynthetic pigments, accessory pigments and elements for transporting electrons, are all included in the thylacoidal membranes containing so-called phycobilisome granules. It is these granules which, in particular, hold phycocyanin, a pigment which is key to delivering energy to the PS-II. Phycocyanin is a protein comprising a polypyrrole-type prosthetic group; this gives it a blue-ish colour, as well as extremely efficient red fluorescence.

Cyanobacteria are able to absorb carbon through the Calvin cycle and they store energy and carbon in the form of glycogen. They have a considerable variety of metabolic structures, but they all share a lack of the full Krebs cycle.

A sizeable number of cyanobacteria, in particular many of the filamentous ones, are capable of nitrogen fixation, thanks to their specialised heterocyst structures.

Learn more (in French) Quelques bases scientifiques et analyse de l’ADN de la spiruline, Antenna Technologies, 2009

Rediscovered in Chad: from dihé to today

The first written records of spirulina date from the 16th century, the time when the Spanish set off on a conquest of South America, and Mexico in particular. It was eaten by the Aztecs who harvested it from lake, water, mixing it with maize to eat.

Spirulina resurfaced in the 1950s, when it was (re-)discovered by a mission of European scientists in Chad. Dried biscuits were found on sale in markets in the Kanem region, green with a blue hue and bearing the name of ‘dihé’. Further enquiries revealed that dihé was made of masses of a single micro-organism harvested from strongly alkaline local waters, and then dried just on the sands along the shoreline.

The micro-organism proved to be capable of photosynthesis and reproduced itself at a rapid pace. It was given the name ‘spirulina’ because of the filamentous spiral that was visible under a microscope. Its botanical name is ‘Arthrospira platensis’.

The Kanem region in Chad is a desert, scattered with small, temporary lagoons known as ‘wadis’. The subsoil is rich in a mixture of carbonates and salt (natron), which makes the waters of the wadi particularly alkaline – it is this medium which is very favourable for micro-algae to grow. Spirulina has been a very special and much sought-after foodstuff for centuries throughout Kanem; it is also heavily traded across the Sahel. At regular intervals, local communities harvest the spirulina from the wadis and filter it with water in tightly-woven wicker baskets. The resulting mass looks like a dark-green purée. To prepare it for conserving and sale, it is dried in the open sun, just lying on the sand. Once dry, it is broken into largish chunks which keep a long time in dry conditions.