Effects of light and low oxygen tension on pigment biosynthesis in Halobacterium salinarum, revealed by a novel method to quantify both retinal and carotenoids.

A novel method for analyzing halobacterial pigments was developed, in which retinal was liberated from halobacterial rhodopsins as retinal oxime by hydroxylamine, ethyl beta-apo-8'-carotenoate was introduced as an internal standard, and the pigments including bacterioruberin and beta-carotene were analyzed by HPLC at the same time. With this method, we revealed that light enhances the biosynthesis of bacterioruberin and the conversion of beta-carotene to retinal, but does not affect beta-carotene biosynthesis in Halobacterium salinarum strain Oyon Moussa-16. Low oxygen tension given in the light brought a slight increase in retinal accumulation, although its biosynthesis from beta-carotene is an oxygenation reaction. This paradox could be explained by the increase in beta-carotene biosynthesis.