Evaluation of the antioxidant effects of carotenoids from Deinococcus radiodurans through targeted mutagenesis, chemiluminescence, and DNA damage analyses.

Deinococcus radiodurans is highly resistant to reactive oxygen species (ROS). The antioxidant effect of carotenoids in D. radiodurans was investigated by using a targeted mutation of the phytoene synthase gene to block the carotenoid synthesis pathway and by evaluating the survival of cells under environmental stresses. The colorless mutant R1DeltacrtB of D. radiodurans failed to synthesize carotenoids, and was more sensitive to ionizing radiation, hydrogen peroxide, and desiccation than the wild type, suggesting that carotenoids in D. radiodurans help in combating environmental stresses. Chemiluminescence analyses showed that deinoxanthin, a major product in the carotenoid synthesis pathway, had significantly stronger scavenging ability on H2O2 and singlet oxygen than two carotenes (lycopene and beta-carotene) and two xanthophylls (zeaxanthin and lutein). Deinoxanthin also exhibited protective effect on DNA. Our findings suggest that the stronger antioxidant effect of deinoxanthin contribute to the resistance of D. radiodurans. The higher antioxidant effect of deinoxanthin may be attributed to its distinct chemical structure which has an extended conjugated double bonds and the presence of a hydroxyl group at C-1' position, compared with other tested carotenoids.