IDENTIFICATION AND SUBCELLULAR-DISTRIBUTION OF CAROTENOIDS IN THE AEROBIC PHOTOSYNTHETIC BACTERIUM, PSEUDOMONAS-RADIORA STRAIN MD-1

The carotenoid compositions in the aerobic methylotrophic photosynthet ic bacterium, Pseudomonas radiora (Methylobacterium radiotolerans) str ain MD-1, were investigated. Carotenoids bound to the BChl-protein com plex were identified as spirilloxanthin, anhydrorhodovibrin and rhodov ibrin, which have been generally found in purple photosynthetic bacter ia. The ratio of BChl alpha to carotenoid in the BChl-protein complex was about 2 to 1. The transfer of excitation energy from carotenoids t o BChl in the BChl-protein complex was observed although its efficienc y was as low as that in the purple bacterial complexes which have spir illoxanthin as the major carotenoid component. By contrast, carotenoic acids were found as major forms of carotenoids in the cells, and most of them were not bound to the BChl-protein complex. These carotenoic acids were also found as the major carotenoids in other methylotrophs that have been characterized as aerobic photosynthetic bacteria.