Carotenoids of thermophilic bacteria— Rhodothermus marinus from submarine Icelandic hot springs

Abstract

The carotenoids (0.04% of dry weight) from Rhodothermus marinus were analysed by semi-preparative HPLC, GCMS, Vis, NMR, CD and EIMS spectroscopy and chemical derivatisations. The carotenoids consisted of (all- E, 2′ S)-2′-hydroxy-1′-(β- d-glucopyranosyloxy)-3′,4′-didehydro-1′,2′-dihydro-β,ψ-caroten-4-one (3.3% of total carotenoid) and its C-6″ acyl derivative (55%), and (all- E)-1′-(β- d-glucopyranosyloxy)-3′,4′-didehydro-1′,2′-dihydro-β,ψ-caroten-4-one (2.5%) and its C-6″ acyl derivative (39%). Both carotenoid acyl glucosides exhibited the same acyl profile. Major esterifying acids were the branched odd-carbon iso-C13:0, anteiso-C13:0, iso-C15:0 and anteiso-C15:0. The extensive branching is compatible with the lipid profile of the bacterium. The remarkable structural conformity between the major carotenoid acyl glucoside from R. marinus and our previous studies on salinixanthin from the extremely halophilic eubacterium Salinibacter ruber is consistent with published results based on sequencing of bacterial 16S rRNA genes. The minor carotenoid acyl glucoside is closely related to the acylated keto-myxocoxanthin glucoside reported from the thermophilic phototrophic bacterium Roseiflexus castenholzii. Carotenoids associated with membrane stabilisation in thermophilic bacteria and in other bacteria living under extreme conditions are discussed.