Evolution from photosynthetic bacteria to cyanobacteria based on carotenoids and carotenogenesis genes

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1. Carotenoids in a novel purple sulfur bacterium(2S)-Spirilloxanthin-2-ol, whose partial structure is similar to that of myxol and stereochemistry is the same with that of (2S)-myxol in cyanobacteria, was identified.2. p-Carotene ketolases in Anabaena sp. PCC 7120Two distinct p-Carotene ketolases, CrtO and CrtW, have been known. CrtO catalyzed β-carotene to echinenone, and CrtW catalyzed myxol to ketomyxol. Nostoc punctiforme have two CrtWs, and the substrate of one is β-carotene, while the other is myxol.3. Phytoene desaturase in Gloeobacter violaseusFor desaturation of phytoene to lycopene, cyanobacteria need three enzymes, CrtP, CrtQ and CrtH. Gloeobacter did not use these enzymes, but used bacterial-type, CrtI. This species is the first example to use CrtI in cyanobacteria.4. Carotenoids in some cyanobacteriaCarotenoids of 19 species including Anabaena, Nostoc and filamentous cyanobacteria, were identified. Glycoside moieties of myxol glycosides were not identified. They had unique ketocarotenoids and myxol glycosides. For carotenogenesis, lycopene cyclase, β-carotene hydroxylase (CrtR), β-carotene 2-hydroxylase (CrtG-like), β-carotene ketolases (CrtO, CrtW) and myxol synthesis enzymes might be included. Various carotenoid compositions may be owing to presence or absence of carotenogenesis gene(s) and/or the substrate specificity of the enzyme(s). These findings are very interesting on the evolution of carotenoids from photosynthetic bacteria to cyanobacteria.