Intracellular bound chlorophyll residues identify 1 Gyr-old fossils as eukaryotic algae
Marie-Catherine Sforna, Corentin Loron, Catherine Demoulin, Camille François, Yohan Cornet, Yannick Lara, Daniel Grolimund, Darío Ferreira Sánchez, Kadda Medjoubi, Andréa Somogyi, Ahmed Addad, Alexandre Fadel, Philippe Compère, Daniël Baudet, Jochen J. Brocks, Emmanuelle Javaux
Abstract
The acquisition of photosynthesis is a fundamental step in the evolution of eukaryotes. However, few phototrophic organisms are unambiguously recognized in the Precambrian record. The in situ detection of metabolic byproducts in individual microfossils is the key for the direct identification of their metabolisms. Here, we report a new integrative methodology using synchrotron-based X-ray fluorescence and absorption. We evidence bound nickel-geoporphyrins moieties in low-grade metamorphic rocks, preserved in situ within cells of a ~1 Gyr-old multicellular eukaryote, Arctacellularia tetragonala. We identify these moieties as chlorophyll derivatives, indicating that A. tetragonala was a phototrophic eukaryote, one of the first unambiguous algae. This new approach, applicable to overmature rocks, creates a strong new proxy to understand the evolution of phototrophy and diversification of early ecosystems.