Carotenoids from the extreme halophilic archaeon Haloterrigena turkmenica: identification and antioxidant activity

Haloterrigena turkmenica was able to synthesize carotenoids when grown in halobacteria medium. These molecules have antioxidant properties and find application in food, cosmetic, and pharmaceutical fields. The carotenoids were extracted with methanol, separated by RP-HPLC, and identified by mass spectrometry and UV/Vis spectra analyses. The C50 carotenoids were the main pigments, and C30, C40, and C51 carotenoids were also detected. Seven geometric isomers were distinguished for bacterioruberin, monoanhydrobacterioruberin, and bisanhydrobacterioruberin. The assignment to a specific isomer was tentatively attempted through the analysis of the corresponding UV/Vis spectrum, the intensity of the cis peak, and its spectral fine structure. Lycopene, phytoene, and lycopersene were among the minor carotenoids further identified. The extract displayed antioxidant power higher than alpha-tocopherol, butylhydroxytoluene, and ascorbic acid used as reference compounds. Our studies identified for the first time seven geometric isomers of bacterioruberin derivatives and 30 carotenoids in a haloarchaeon.