Bacterioruberin and salinixanthin carotenoids of extremely halophilic Archaea and Bacteria: A Raman spectroscopic study

Laboratory cultures of a number of red extremely halophilic Archaea (Halobacterium salinarum strains NRC-1 and R1, Halorubrum sodomense, Haloarcula valismortis) and of Salinibacter ruber, a red extremely halophilic member of the Bacteria, have been investigated by Raman spectroscopy using 514.5 nm excitation to characterize their carotenoids. The 50-carbon carotenoid α-bacterioruberin was detected as the major carotenoid in all archaeal strains. Raman spectroscopy also detected bacterioruberin as the main pigment in a red pellet of cells collected from a saltern crystallizer pond. Salinibacter contains the C₄₀-carotenoid acyl glycoside salinixanthin (all-E, 2′S)-2′-hydroxy-1′-[6-O-(methyltetradecanoyl) -β-d-glycopyranosyloxy]-3′,4′-didehydro-1′, 2′-dihydro-β,ψ-carotene-4-one), for which the Raman bands assignments of are given here for the first time.