Removal of Photosystem I Subunit PsaE Leads to Photosynthetic Hydrogen Production in a Cyanobacterial PsaF‐HoxYH Fusion Strain

Photosynthetic hydrogen (photoH 2 ) production is a promising approach for the utilisation of solar energy. Fusion of a hydrogenase (H 2 ase) to photosystem I (PSI) provides a direct light‐driven route for photoH 2 generation. We established the lateral transmembrane subunit PsaF of PSI as a new fusion partner for the NiFe‐hydrogenase (HoxYH) in the cyanobacterium Synechocystis sp. PCC 6803. Gradual reduction of PsaC expression in a PsaF‐HoxYH strain was established to access the most redox negative FeS‐cluster F X of PSI, but this did not result in photoH 2 production. In another approach PSI subunit PsaE was identified as a potential steric hindrance in the psaF‐hoxYH strain to electron transfer between the FeS‐cluster F B cluster in PSI and HoxYH. Consistent with this, deletion of PsaE in psaF‐hoxYH led to successful photoH 2 production. Our results identify PsaF as a viable and structurally favourable anchor providing a new strategy for the engineering of photobiological H 2 ‐production systems.