Abstract
Cyanobacteria essentially have various carotenoids for light-harvesting and photoprotection. They have unique carotenoids of carotenoid methylpentosides and ketocarotenoids, such as myxol 2'-fucoside and echinenone. Genome DNA sequences of more than 40 species and/or strains have been determined, but carotenoids in some species are not identified. We performed the BLAST-search for carotenogenesis genes with the chosen query sequences, whose functions have already been confirmed. We found that some homologues have no functions themselves or there are no carotenoids of products. Some genes cannot be found from homologous search but products are present. The different compositions of carotenoids among these species might be due to the presence or absence of certain gene(s), or to different enzyme characteristics including substrate specificities. Two distinct β-carotene hydroxylases, CrtR and CrtG, are bifunctional enzymes. Two distinct β-carotene ketolases, CrtO and CrtW, are properly used in two pathways depending on the species.
