Carotenoid 3',4'-desaturase is involved in carotenoid biosynthesis in the radioresistant bacterium Deinococcus radiodurans

Key Laboratory for Nuclear-Agricultural Sciences of Chinese Ministry of Agriculture and Zhejiang Province, Institute of Nuclear-Agricultural Sciences, Zhejiang University, 310029 Hangzhou, PR China Correspondence Yuejin Hua yjhua{at}zju.edu.cn Deinococcus radiodurans strain R1 synthesizes deinoxanthin, a unique carotenoid product, which contributes to cell resistance following various stresses. The biosynthetic pathway of deinoxanthin is unclear, although several enzymes are presumed to be involved. The gene ( dr2250 ) predicted by gene homologue analysis to encode carotenoid 3',4'-desaturase (CrtD) was deleted to investigate its function. A mutant deficient in the gene homologue of crtLm ( dr0801 ) was also constructed to verify the catalytic function of the gene product in the native host. Carotenoid analysis of the resultant mutants verified that DR2250 encodes carotenoid 3',4'-desaturase, which catalyses the C-3',4'-desaturation of the monocyclic precursor of deinoxanthin but not acyclic carotenoids. Mutation of the gene homologue of crtLm ( dr0801 ) resulted in accumulation of lycopene, confirming that it encodes the lycopene cyclase in the native host. The lack of CrtD decreased the antioxidant capacity of the mutant deficient in dr2250 compared with the wild-type, indicating that the C-3',4'-desaturation step contributes to the antioxidant capacity of deinoxanthin in D. radiodurans . Abbreviations: APCI, atmospheric pressure chemical ionization; DCFH-DA, 2',7'-dichlorohydrofluorescein diacetate; PQQ, pyrroloquinoline quinone; ROS, reactive oxygen species Details of plasmid construction and absorbance spectra of peaks 2 and 2' are available as supplementary material with the online version of this paper.