Chlorella vulgaris

Chlorella vulgaris is a species of green microalga in the Division Chlorophyta. It is mainly used as a dietary supplement or protein-rich food additive in Japan.
Introduction.
"C. vulgaris" is a green eukaryotic microalga in the genus "Chlorella", which has been present on earth since the Precambrian period. This unicellular alga was discovered in 1890 by Martinus Willem Beijerinck as the first microalga with a well-defined nucleus. At the beginning of the 1990s, German scientists noticed the high protein content of "C. vulgaris" and began to consider it as a new food source. Japan is currently the largest consumer of Chlorella, both for nutritional and therapeutic purposes.
Symbiosis.
"Chlorella vulgaris" occurs as a symbiont in tissues of the freshwater flatworms "Dalyellia viridis and Typhloplana viridata".
Production.
The world annual production of the various species of "Chlorella" was 2000 tonnes (dry weight) in 2009, with the main producers being Germany, Japan and Taiwan. "C. vulgaris" constitutes an excellent candidate for production due to its high resistance against rough conditions and invading organisms. In addition, the production of the various organic macromolecules of interest (proteins, lipids, starch) differ depending on the technique used to create biomass and can be therefore targeted. Under more hostile conditions, the biomass decreases but lipids and starch contents increase. Under favourable conditions, protein content raises along with the biomass. Different growth techniques have been developed. They exploit the autotrophic, heterotrophic or mixotrophic properties of "C. vulgaris". Growing "C. vulgaris" autotrophically is illustrated by the closed photo-bioreactor. Harvesting the biomass is then generally done by centrifugation due to the high process efficiency (95% recovery). Other techniques exist, such as flocculation, filtration and flotation.
Uses.
Bioenergy.
"C. vulgaris" is seen as a promising source of bioenergy. It may be a good alternative to biofuel crops, like soybean, corn or rapeseed, as it is more productive and does not compete with food production. It can produce large amount of lipids, up to 20 times more than crops that have a suitable profile for biodiesel production. This microalgae also contains high amounts of starch, good for the production of bioethanol. However, microalgal biofuels are far from competitive with fossil fuels, given their high production costs and controversial sustainability.
Food.
The proteins content of "C. vulgaris" varies from 42 to 58% of its biomass dry weight. These proteins are considered as having a good nutritional quality compared to the standard profile for human nutrition of the World Health Organization and Food and Agriculture Organization, as the algae synthesizes amino acids. The algae also contains lipids (5–40% of the dry mass), carbohydrates (12–55% dry weight) and pigments with among others chlorophyll, reaching 1–2 % of the dry weight. 
"C. vulgaris" contains minerals and vitamins. "C. vulgaris" is marketed as dietary supplement, additive, as colourant or food emulsion. They are all in the form of capsules, extracts, tablets or powder. They are consumed in Japan as a medical treatment. However, despite its high protein content, "C. vulgaris" is not yet widely incorporated in food products. The main reason for this is its dark green colour and its smell, which is close to that of fish. Vitamin B12, specifically in the form of methylcobalamin, has been identified in "Chlorella vulgaris".
In popular culture.
In Alan Dean Foster's short story, "Village of the Chosen", published in The Best of Omni in 1983, a pair of scientists engineer a strain of Chlorella to be in symbiosis with humans, so humans can become photosynthetic.