Intracellular bound chlorophyll residues identify 1 Gyr-old fossils as eukaryotic algae

Area of Science:

• Paleobiology
• Biogeochemistry
• Evolutionary Biology

Background:

• The evolution of photosynthesis in eukaryotes is crucial for understanding early life.
• Identifying Precambrian phototrophs is challenging due to limited fossil evidence.
• Detecting metabolic byproducts in microfossils is key to identifying ancient metabolisms.

Observation:

• A novel integrative methodology using synchrotron-based X-ray fluorescence and absorption was developed.
• Bound nickel-geoporphyrins moieties were detected in situ within cells of Arctacellularia tetragonala.
• These moieties were identified as chlorophyll derivatives.

Findings:

• Arctacellularia tetragonala, a ~1 billion-year-old multicellular eukaryote, possessed chlorophyll derivatives.
• This provides unambiguous evidence of phototrophy in this ancient organism.
• The findings represent one of the earliest confirmations of algal phototrophy.

Implications:

• This new approach enables the study of phototrophy in overmature rocks.
• It offers a powerful new proxy for reconstructing early ecosystems and evolutionary history.
• The discovery enhances our understanding of eukaryotic diversification and the rise of photosynthesis.