Abstract
Important functions of carotenoids in photosynthetic organisms are protection against photooxidative damage and light-harvesting. Nevertheless, the correlation between the chemical structure of carotenoids and their function has not yet been clarified. To assess functional features of cyclic carotenoids, we have constructed mutants of the purple photosynthetic bactererium, Rubrivivax gelatinosus (IL144), that accumulated cyclic carotenoids. To construct a Β-carotene-accumulating mutant, lycopene cyclase gene (crtY) from Pantoena ananatis (Erwinia uredovora) was introduced into the lycopene-accululating mutant. Then, crtW and/or crtZ from Paracoccus sp. N81106 (Agrobacterium aurantiacum) were introduced to this mutant to obtain three mutants synthesizing canthaxanthin, zeaxanthin and astaxanthin.
These cyclic carotenoids were found in cytoplasm, membranes and pigment-proteins. It was suggested that the cyclic carotenoids could function as antenna pigments for growth of the purple bacterium. Resistance of the mutants against singlet oxygen was as high as the wild-type Rvi. gelatinosus that accumulates spheroidenone in the presence of O2.
