cyanobacteria Photosynthesis
Marine and freshwater cyanobacteria protect themselves from overexcitation by activating the Orange Carotenoid Protein (OCP). The OCP is activated by strong light illumination, changing from its orange to red state. The picture depicts three bacteria, one in full sunlight (top, reddish), one in the shade (bottom, orange hue) and one in the middle. Dvir Harris et al, PNAS 2016, have proposed a mechanism by which, after activation, the N-terminal domain of the OCP burrows in between units of the Phycobilisome antenna complex, thereby diminishing the flow of energy to the reaction centers.
The Genius of NATURE

Photosynthesis is the process by which plants and other organisms use sunlight to synthesize nutrients from carbon dioxide and water. Photosynthesis is essential to the animal kingdom: not only for organisms that perform photosynthesis themselves, but for all living things. This is because even animals that do not perform photosynthesis consume the primary product of photosynthesis – glucose. Just as the film in pre-digital cameras can be overexposed, natural photosynthetic systems are also liable to become impaired as a result of overexposure, leading to the death of the organism.

Photosynthesis is a sophisticated process within which, the genius of nature is still being understood. The recent Technion research throws light on the mechanisms of these organisms to protect the system from overexposure to sunlight. One of these defense mechanisms has now been revealed in a study conducted by Prof. Noam Adir and doctoral student Dvir Harris of the Schulich Faculty of Chemistry, in collaboration with Dr. Diana Kirilovsky and her laboratory at I2BC-CEA, in France. The article was published in the Proceedings of the National Academy of Sciences (PNAS). The defense mechanism was deciphered in cyanobacteria (often called “blue-green algae”). The main player in this mechanism is the protein OCP – a protein that modifies its structure and color in response to intense light.

This change blocks the flow of energy that reaches the photosynthetic reaction center by means of a reaction between the active species of OCP and phycobilisome (PBS), the protein complex that functions as a light-harvesting antenna in the cyanobacteria. “In this study we discovered how the OCP blocks the energy,” explains Prof. Adir. “In effect, the protein acts as a biological switch. In response to strong light, part of the protein penetrates into the PBS, changes the PBS structure, thereby diverting the flow of energy from the reaction centers. According to experiments  performed in the Kirilovsky lab, this defense mechanism blocks more than 90% of the sun’s radiation. As soon as the radiation diminishes, the protein returns to its normal state and the flow of energy resumes.”


Technion science has revealed how during photosynthesis, tiny bacteria protect themselves from the more harmful aspects of the sun’s rays.