Unique Carotenoids in the Terrestrial Cyanobacterium Nostoc commune NIES-24: 2-Hydroxymyxol 2′-Fucoside, Nostoxanthin and Canthaxanthin

Cyanobacteria produce some carotenoids. We identified the molecular structures, including the stereochemistry, of all the carotenoids in the terrestrial cyanobacterium, Nostoc commune NIES-24 (IAM M-13). The major carotenoid was β-carotene. Its hydroxyl derivatives were (3R)-β-cryptoxanthin, (3R,3′R)-zeaxanthin, (2R,3R,3′R)-caloxanthin, and (2R,3R,2′R,3′R)-nostoxanthin, and its keto derivatives were echinenone and canthaxanthin. The unique myxol glycosides were (3R,2′S)-myxol 2′-fucoside and (2R,3R,2′S)-2-hydroxymyxol 2′-fucoside. This is only the second species found to contain 2-hydroxymyxol. We propose possible carotenogenesis pathways based on our identification of the carotenoids: the hydroxyl pathway produced nostoxanthin via zeaxanthin from β-carotene, the keto pathway produced canthaxanthin from β-carotene, and the myxol pathway produced 2-hydroxymyxol 2′-fucoside via myxol 2′-fucoside. This cyanobacterium was found to contain many kinds of carotenoids and also displayed many carotenogenesis pathways, while other cyanobacteria lack some carotenoids and a part of carotenogenesis pathways compared with this cyanobacterium.