Hydrogen isotope fractionation during lipid biosynthesis by Tetrahymena thermophila

The δD values of FAs and tetrahymanol correlated linearly with the hydrogen isotope composition of water, but growth temperature was also clearly an important factor controlling lipid D/H compositon. Hydrogen isotope fractionation during tetrahymanol biosynthesis changed with higher growth temperatures, resulting in D-depleted signatures relative to water at 24 °C and 30 °C and D-enriched composition at 36 °C. T. thermophila grown at 36 °C - a temperature above opitmum growth conditions - showed a significant change in lipid composition, with the abundance of tetrahymanol increasing relative to total FAs. We suggest the change is a response to temperature stress and a decrease in the stability of the cell membrane. The temperature effect is also presumed to impact δDlipid by altering the hydrogen isotopic composition of NADPH and potentially intracellular water.