Accumulation of unusual carotenoids in the spheroidene pathway, demethylspheroidene and demethylspheroidenone, in an alkaliphilic purple nonsulfur bacterium Rhodobaca bogoriensis

Abstract

Carotenoids extracted from cells of a novel alkaliphilic purple nonsulfur bacterium Rhodobaca bogoriensis strain LBB1 included unusual carotenoids in the spheroidene pathway; demethylspheroidene, demethylspheroidenone, neurosporene and spheroidenone. Spheroidene was present in only small amounts, and the demethyl-carotenoids demethylspheroidene and demethylspheroidenone predominated in phototrophic cultures. Furthermore, the keto-carotenoids spheroidenone and demethylspheroidenone constituted nearly half of the total carotenoids, even in strict anaerobic phototrophic cultures. Spheroidenone was, however, the sole carotenoid in aerobic cultures. Phototrophic cultures of Rbc. bogoriensis were yellow in colour and quite distinct from the brown-red colour of cultures of Rhodobacter species. The carotenogenesis pathways of Rhodobaca and Rhodobacter species are compared with special reference to two key enzymes of the spheroidene pathway, CrtA and CrtF, whose activities are thought to be responsible for the unusual carotenoid composition of Rhodobaca. This bacterium also contained bacteriochlorophyll a _p and ubiquinone-10.