An international team of scientists has decoded the structure of the light-harvesting complex of Photosystem I (PSI) in the ancient cyanobacterium Anthocerotibacter panamensis, marking a major step toward understanding the origins of oxygenic photosynthesis — the process that dramatically transformed Earth’s atmosphere. This bacterium represents a unique evolutionary branch that split off around 3 billion years ago and serves as a kind of “time capsule” of early photosynthesis. Unlike most modern photosynthetic organisms, A. panamensis lacks thylakoids — specialized membranes — making its photosynthetic machinery less efficient but more primitive in design.
Using cryo-electron microscopy, researchers found that the structure of PSI in this organism has remained virtually unchanged for billions of years. The complex resembles a three-leaf clover and includes more than 300 light-absorbing pigments. This indicates that the photosynthetic mechanism had already reached a high level of complexity at an early evolutionary stage. The authors suggest that oxygenic photosynthesis may have even emerged before the cyanobacteria themselves.
Decoding the PSI structure allows scientists to more accurately reconstruct the history of photosynthesis by distinguishing ancient elements from later evolutionary developments. These findings are important not only for evolutionary biology but also for synthetic biology, as they may aid in designing more efficient solar energy conversion technologies. The research highlights the durability of core photosynthetic mechanisms and opens new avenues for exploring the origins of photosynthesis in even more ancient microorganisms.
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