Abstract
One of the important functions of carotenoids in photosynthetic organisms is protection against photooxidative damage. In this study, we compared photoprotective functions of carotenoid species by using six mutants of purple photosynthetic bacterium, Rubrivivax gelatinosus. Growth analysis under aerobic high-light conditions and viability analysis under artificially generated singlet oxygen showed that neurosporene and spheroidene have rather low photoprotective function. Although lycopene and spirilloxanthin showed significant photoprotective function in the growth analysis, these carotenoids showed relatively low activity in scavenging singlet oxygen. Keto-carotenoids, diketospirilloxanthin and spheroidenone, showed highest protective activity against oxidative damage than other carotenoids. It was suggested that the high protective activity of keto-carotenoid is caused by the presence of keto group, and not by the length of conjugated double bonds.
