Role of carotenoids in adaptation of the photosynthetic bacterium Rhodobacter sphaeroides to growth conditions

The purple non-sulfur bacterium Rhodobacter sphaeroides call grow under aerobic (chemoheterotrophic) and anaerobic (photosynthetic) conditions. Two photosynthetic antenna complexes, LH1 and LH2, are synthesized at various ratios depending on illumination intensity during anaerobic growth. Carotenoids including spheroiden and spheroidenone, bacteriochlorophyll, and structural polypeptides are components of the antenna complexes. Spheroiden predominates in the LH2 complex and spheroidenone is detected only in the LH1 complex. Accumulation of the two major carotenoids depends on the stoichiometry of the photosynthetic complexes. Carotenoids can participate in the regulation of LH1 and LH2 formation and adaptation of R. sphaeroides to changes in illumination intensity during photosynthetic growth.