Fractionation Of Hydrogen Isotopes During Lipid-Biosynthesis By Tetrahymena thermophila, Dunaliella bardawil and Haloarcula marismortui

Paleoclimatological research is mainly based on proxies that reflect different climatic variations. Organic compounds preserved in sediments form a very important group of proxies, of which lipids are an important class. Recently, attention has been directed toward understanding the magnitude of hydrogen isotope fractionation that occurs during lipid biosynthesis given its potential as a proxy for understanding changes in the hydrological system. Hydrogen isotope ratios of lipids depend on hydrogen isotopic composition of the ambient water, which in turn is dependent on hydrological conditions. Hydrogen isotope ratios of lipids also depend on the biosynthetic pathway, which causes differences between hydrogen isotope ratios of lipids synthesized by different organisms. The application of lipids derived from multiple source organisms (e.g. fatty acids) are less useful for reconstructing hydrogen isotopic compositions of ambient water, because of the lack of specificity regarding its source. On the other hand, lipids that are synthesized by specific kinds of organisms or lipids that in a specific environment are synthesized by specific kinds of organisms are more useful for reconstructing hydrogen isotopic compositions of the ambient water. For this study, we are investigating the hydrogen isotope fractionation between ambient water and lipids that are derived from specific organisms from hypersaline environments. Specifically, we have grown three organisms that are abundant in saline to hypersaline environments, including Tetrahymena thermophila (Protozoa), Dunaliella bardawil (Alga), and Haloarcula marismortui (Archaea) in pure cultures and are in the process of evaluating isotopic variability of specific lipids (i.e. Tetrahymanol in Tetrahymena, beta-carotene and Stigmasterol in Dunaliella, and archaeol in Haloarcula) and other non-specific fatty acids associated with the D/H composition of ambient water, growth temperature and salinity.