Impact of metabolic pathways and salinity on the hydrogen isotope ratios of haptophyte lipids

Abstract

Hydrogen isotope ratios of biomarkers have been shown to reflect water isotope ratios, and in some cases correlate significantly with salinity. The δ 2 H-salinity relationship is best studied for long-chain alkenones, biomarkers for haptophyte 20 algae, and is known to be influenced by a number of different environmental parameters. It is not fully known why δ 2 H ratios of lipids retain a correlation to salinity, and whether this is a general feature for other lipids produced by haptophyte algae.Here, we analyzed δ 2 H ratios of three fatty acids, brassicasterol, long-chain C37 alkenones and phytol from three different haptophyte species grown over a range of salinities. Lipids synthesized in the cytosol, or relying on precursors of cytosolic origin, show a correlation between their δ 2 H ratios and salinity. In contrast, biosynthesis in the chloroplast, or utilizing 25 precursors created in the chloroplast, yields lipids that do not show a correlation between δ 2 H ratios and salinity. This leads to the conclusion that location of metabolism is the first-order control on the salinity signal retained in δ 2 H ratios of certain lipids.Additionally, we found that δ 2 H ratios of alkenones from batch cultures of the Group II haptophyte species Tisochrysis lutea correlate positively with temperature, contrary to findings from cultures of Group III haptophytes, but retain a similar response to nutrient availability in line with other Group III haptophytes. 30 Biogeosciences Discuss., https://doi.

Fatty Acids Derivatives From Eukaryotic Microalgae, Pathways and Potential Applications

“…Little is known about the biosynthesis of alkenones. Since alkenone concentration was found to increase under nitrogen-deprivation ( Eltgroth et al, 2005 ; Tsuji et al, 2015 ; Weiss et al, 2019 ), and their degree of unsaturation varies at changing temperatures ( Araie et al, 2018 ) analogously to fatty acids, they have been suggested to be produced in the chloroplasts and to be formed from fatty acids. Since alkenones attract also biotechnological interest, current research is focusing on delineating the biosynthetic pathways of such compounds and to develop genetically engineered strains with increased alkenone concentrations 2 .…”

Stable Middle Miocene seawater isotopes in the eastern North Atlantic Ocean

“…Hydrogen isotope ratios of alkenones of 124 fractions (99 from the original sample set of Sangiorgi et al, 2021 and 25 additional samples) were measured in duplicate using a gas chromatograph coupled to a Thermo Delta V isotope ratio mass spectrometer via hightemperature conversion reactor (Isolink I) and Conflo IV. The GC was equipped with an RTX-200 60 m column according to Weiss et al (2019). We report the δ 2 H ratio of alkenone C 37:2 determined by manual peak integration.…”