Photosynthesis is a fundamental biological process that has considerably shaped our world and the atmosphere surrounding it. The process is so inspiring that besides the plants that are absorbing carbon dioxide and releasing oxygen, even scientists are working on developing artificial photosynthesis systems that can generate fuel for us.
But now, researchers detected that an unusual species of bacteria that is discovered eight years ago in the Gobi desert conducts an ancient form of photosynthesis. The bacterium is dubbed Gemmatimonas phototrophica and it contains a molecular, light-eating device that is unprecedented.
"The architecture of the complex is very elegant. A real masterpiece of nature" says Dr. Michal Koblizek from the Institute of Microbiology at Czech Academy of Sciences. "It has not only good structural stability, but also great light harvesting efficiency."
According to a paper published on 16 February in Science Advances, the bacterium has evolved its ability of photosynthesis via the horizontal transfer of photosynthesis-related genes from a more ancient phototrophic proteobacterium.
The structure of the photosynthesis complex
The complex of molecules allowing the bacterium's photosynthesis has two layers of rings around the reaction center. The outer ring functions to snatch the sunlight and transfer it from its 800 and 816 nm absorption bands to the 868 nm absorption of the inner ring. Then the captured protons are conveyed to the reaction center, which transforms the absorbed light energy into an electrical charge.
The photosynthesizing complex resembles a funnel. First, the energy is absorbed by the pigments around the structure and transferred from the energy gradient to the center of the complex where it is converted into metabolic energy. The whole process takes only several picoseconds.
"This structural and functional study has exciting implications because it shows that G. phototrophica has independently evolved its own compact, robust, and highly effective architecture for harvesting and trapping solar energy," says Dr. Pu Qian, University of Sheffield structural biologist and the lead author of the study.
Phototrophic Gemmatimonadetes evolved the ability to use solar energy following horizontal transfer of photosynthesis-related genes from an ancient phototrophic proteobacterium. The electron cryo-microscopy structure of the Gemmatimonas phototrophica photosystem at 2.4 Å reveals a unique, double-ring complex. Two unique membrane-extrinsic polypeptides, RC-S and RC-U, hold the central type 2 reaction center (RC) within an inner 16-subunit light-harvesting 1 (LH1) ring, which is encircled by an outer 24-subunit antenna ring (LHh) that adds light-gathering capacity. Femtosecond kinetics reveal the flow of energy within the RC-dLH complex, from the outer LHh ring to LH1 and then to the RC. This structural and functional study shows that G. phototrophica has independently evolved its own compact, robust, and highly effective architecture for harvesting and trapping solar energy.