Carotenoids in Phototrophic Microalgae: Distributions and Biosynthesis

Phototrophic organisms necessarily synthesize not only carotenoids but also chlorophylls for photosynthesis. Phototrophic microalgae are usually single-cell organisms; however, as the pigment compositions of both single-cell and macrophytic types are almost identical, both are included in this chapter. Further, many kinds of carotenoids have been identified and, recently, taxonomic studies of algae have been developed. In this review, the relationship between the distributions of carotenoids and the phylogeny of oxygenic phototrophs, including cyanobacteria, red algae, brown algae, and green algae, in sea and fresh water is summarized. These phototrophs contain division- or class-specific carotenoids, such as fucoxanthin, peridinin, diadinoxanthin, and siphonaxanthin. Carotenogenic pathways are discussed in terms of the chemical structures of carotenoids and known characteristics of the enzymes involved with carotenogenesis in other organisms, as the algal genes and enzymes associated with carotenogenesis have not yet been identified. Additionally, some procedures for the general identification of carotenoids are outlined.