Characterization of canthaxanthin isomers isolated from a new soil Dietzia sp. and their antioxidant activities.

Canthaxanthin (cx) is a potent antioxidant that is chemically synthesized at the industrial scale and has imperative applications in the cosmetic and feed industries. An orange pigmented mesophilic bacterium, designated as K44, was isolated from soil samples of Kargil, India. Biochemical tests, 16S rRNA gene sequencing, and FAME analysis of the bacterium indicated it to belong in the genus Dietzia and is distinct from human isolates. The strain showed 98% 16S rRNA gene sequence homology with Dietzia maris DSM 43102. High-performance liquid chromatography profile of the pigments isolated from K44 showed two major peaks absorbing at 465.3 and 475 nm. The liquid chromatography-mass spectrometry (LC-MS) analysis of both these peaks revealed their m/z to be 564. The molecular weights, LC-MS/MS fragmentation patterns, and lambdamax of these fractions corresponded to all-trans- (475 nm) and 9-cis-(465.3 nm) cx isomers. The antioxidant activities of cis- and trans-cx isomers isolated from this bacterium were found to differ, where the cis-isomer showed higher free radical, superoxide radical, and reactive oxygen species scavenging activities than the alltrans- isomer, suggesting that 9-cis-cx is more effective as an antioxidant than the all-trans-cx.