Secondary carotenoid production in green algae

Carotenoids are widespread in living organisms. All the photosynthetic organisms contain carotenoids in their thylakoid membranes performing important role in the photochemical functions. Some green algae produce large amounts of carotenoids which accumulate outside the thylakoids and are known as secondary carotenoids. Two such organisms which have commercial importance are Dunaliella and Haematococcus which produce beta-carotene and astaxanthin, respectively. In this paper we discuss the biosynthetic pathway of carotenoids in these two organisms and the conditions under which they are synthesized. Their physiological role and commercial importance is also dealt with. For commercially viable production of these carotenoids, the existing strains can be improved to have carotenoid overproducing strains. Genes responsible for carotenoid synthesis are being isolated and this shall facilitate rapid strides in the research towards understanding their biosynthesis and further manipulation.