Title | Hydrogen isotope fractionation is controlled by CO $_\textrm2$ in coccolithophore lipids |
Publication Type | Journal Article |
Year of Publication | 2024 |
Authors | Torres-Romero I, Zhang H, Wijker RS, Clark AJ, McLeod RE, Jaggi M, Stoll HM |
Journal | Proceedings of the National Academy of Sciences |
Volume | 121 |
Pagination | e2318570121 |
ISSN | 0027-8424, 1091-6490 |
Keywords | RCC1303 |
Abstract | Hydrogen isotope ratios (δ 2 H) 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 2 H/ 1 H fractionation in algal lipids by systematically manipulating temperature, light, and CO 2 (aq) in continuous cultures of the haptophyte Gephyrocapsa oceanica . We analyze the hydrogen isotope fractionation in alkenones (α alkenone ), a class of acyl lipids specific to this species and other haptophyte algae. We find a strong decrease in the α alkenone with increasing CO 2 (aq) and confirm α alkenone correlates with temperature and light. Based on the known biosynthesis pathways, we develop a cellular model of the δ 2 H 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 2 H-richer intracellular water, increasing α alkenone . Higher chloroplast CO 2 (aq) and temperature shorten NADPH residence time by enhancing the carbon fixation and lipid synthesis rates. The inverse correlation of α alkenone to CO 2 (aq) in our cultures suggests that carbon concentrating mechanisms (CCM) do not achieve a constant saturation of CO 2 at the Rubisco site, but rather that chloroplast CO 2 varies with external CO 2 (aq). The pervasive inverse correlation of α alkenone with CO 2 (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, α alkenone may be a powerful tool to elucidate the carbon limitation of photosynthesis. |
URL | https://pnas.org/doi/10.1073/pnas.2318570121 |
DOI | 10.1073/pnas.2318570121 |