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 β-apo-8'-carotenoate was introduced as an internal standard, and the pigments including bacterioruberin and β-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 β-carotene to retinal, but does not affect β-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 β-carotene is an oxygenation reaction. This paradox could be explained by the increase in β-carotene biosynthesis.