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HOPSEP Report Summary

Project ID: 293579
Funded under: FP7-IDEAS-ERC
Country: Israel

Final Report Summary - HOPSEP (Harnessing Oxygenic Photosynthesis for Sustainable Energy Production)

The study of oxygenic photosynthesis is crucial for the pursuit of sustainable solutions to the striking problems of food security, energy and global warming. This is a very intricate process, which converts light energy into chemical energy. The initial step of the energy conversion is performed by two protein mega-complexes named photosystem I and photosystem II (PSI; PSII).
PSI is one of the major protein complexes in nature. During our project we have had considerable achievements in solving the crystal structure of PSI from various organisms from higher plants to cyanobacteria. The crystal structure of this mega Dalton complex from the mesophilic cyanobacterium Synechocystis was solved to 2.5 Å resolution. The structure obtained contains 33 protein subunits, 285 chlorophyll a molecules, 72 carotenoids, 51 lipids, 9 iron sulfur clusters and 6 calcium ions. In addition, the structure of PSI from Cyanidioschyzon merolae, a red alga, was solved to 4 Å resolution, and PSI from Plant was solved to 2.4 Å resolution revealing the positions of most atoms in this 0.65 mega Dalton membrane complex. Several experiments of subunits deletion, virus-mimetic PSI and the reliance and robustness of the system suggest possible practical implications including photovoltaic devices and photosynthetic hydrogen production.
Hydrogen(H2) production occurs in some micro-organisms as a minor by-product of photosynthesis. Its major restricting factor is oxygen production during photosynthesis. As hydrogen can be used as a clean fuel, exploiting this process is of major interest. At the present time, there are several biochemical and engineering constraints preventing microalgal H2 production at an industrial scale, mainly the simultaneous oxygen and hydrogen production. In this project, we aimed to provide an experimental platform for a novel engineering concept using the microalgae Chlamydomonas reinhardtii, as a model organism to solve those obstacles. Our concept relies on a cyclic H2 production system in which the oxygen (O2) evolving reaction is conditionally inactivated at high temperature to allow sustainable H2 production. Toward this aim we generated Photosystem II temperature-sensitive mutants that allow for the first time spatial separation of oxygen and hydrogen production. The entire system was evaluated by building a cyclic reactor that proved the feasibility of our system. At lower temperatures, cells will grow in a “regular” fashion, converting sunlight, water, and CO2 into organic matter while producing oxygen. Following this growth stage, cells will be shifted to a high temperature–oxygen free environment where oxygen evolution will shut down due to PSII inactivation and hydrogen will be generated. Following identification of the desired mutants we will generate them into a target organism such as the microalga Dunaliella salina that is amenable for large-scale growth and resistant to contamination due to its growth environment.

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