Molecular and isotopic characterization of lipids in cultured halophilic microorganisms from the Dead Sea and comparison with the sediment record of this hypersaline lake

Cultures of the only photosynthetic green alga (Dunaliella parva) in the surface waters of the Dead Sea and three halophilic archaea (Haloarcula marismortui; Haloferax volcanii; Halorubrum sodomense) from the same location were analyzed for their lipid content to investigate the contribution of these organisms to the organic matter in the sediments of this hypersaline lake. Based on distribution patterns and stable carbon isotope ratios, most of the sedimentary short chain saturated and unsaturated fatty acids may be attributed to the green alga, whereas the relatively abundant long chain acids are considered to be predominantly of allochthonous origin. Two Δ7 sterols in the sediments also occur in the alga. Based on carbon isotope data, sedimentary phytol probably has a mixed origin, whereas n-alkanols and n-alkanes were contributed to the sediments from terrestrial sources. The extractable lipid compositions of the three archaea are very similar and dominated by squalenes with different degrees of unsaturation and by glycerol diphytanyl diether (archaeol). Whereas archaeol is also a major constituent of the extractable organic matter in the sediments, the squalenes apparently do not survive sedimentation unaltered; the same is true for the small amounts of less common unsaturated analogues of archaeol in the archaea.