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The conversion of solar energy into hydrogen represents a highly attractive strategy for the production of renewable energies. Photosynthetic microorganisms have the ability to produce H₂ from sunlight but several obstacles must be overcome before obtaining a sustainable and efficient H₂ production system. Cyanobacteria harbor [NiFe] hydrogenases required for the consumption of H₂. As a result, their H₂ production rates are low, which makes them not suitable for a high yield production. On the other hand, [FeFe] enzymes originating from anaerobic organisms such as Clostridium exhibit much higher H₂ production activities, but their sensitivity to O₂ inhibition impairs their use in photosynthetic organisms. To reach such a goal, it is therefore important to protect the hydrogenase from O₂. The diazotrophic filamentous cyanobacteria protect their nitrogenases from O₂ by differentiating micro-oxic cells …