Hydrogen isotope fractionation is controlled by CO2 in coccolithophore lipids

• 成果类型: Article
• 署名作者: Romero, Ismael Torres; Zhang, Hongrui; Wijker, Reto S.; Clark, Alexander J.; McLeod, Rachel E.; Jaggi, Madalina; Stoll, Heather M.
• 署名单位: Swiss Federal Institutes of Technology Domain; ETH Zurich
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-11859
• DOI: 10.1073/pnas.2318570121
• 发表日期: 2024-06-25
• 关键词: carbon-concentrating mechanisms; alkenone delta-d; salinity; GROWTH; water; temperature; algae; light; alkalinity; indicator

摘要

Hydrogen isotope ratios (delta H-2) represent an important natural tracer of metabolic processes, but quantitative models of processes controlling H-fractionation in aquatic photosynthetic organisms are lacking. Here, we elucidate the underlying physiological controls of H-2/H-1 fractionation in algal lipids by systematically manipulating temperature, light, and CO2(aq) in continuous cultures of the haptophyte Gephyrocapsa oceanica. We analyze the hydrogen isotope fractionation in alkenones (alpha(alkenone)), a class of acyl lipids specific to this species and other haptophyte algae. We find a strong decrease in the alpha(alkenone) with increasing CO2(aq) and confirm alpha(alkenone) correlates with temperature and light. Based on the known biosynthesis pathways, we develop a cellular model of the delta H-2 of algal acyl lipids to evaluate processes contributing to these controls on fractionation. Simulations show that longer residence times of NADPH in the chloroplast favor a greater exchange of NADPH with H-2-richer intracellular water, increasing alpha(alkenone). Higher chloroplast CO2(aq) and temperature shorten NADPH residence time by enhancing the carbon fixation and lipid synthesis rates. The inverse correlation of alpha(alkenone) to CO2(aq) in our cultures suggests that carbon concentrating mechanisms (CCM) do not achieve a constant saturation of CO2 at the Rubisco site, but rather that chloroplast CO2 varies with external CO2(aq). The pervasive inverse correlation of alpha(alkenone) with CO2(aq) in the modern and preindustrial ocean also suggests that natural populations may not attain a constant saturation of Rubisco with the CCM. Rather than reconstructing growth water, alpha(alkenone) may be a powerful tool to elucidate the carbon limitation of photosynthesis.