Solar hydrogen-producing bionanodevice outperforms natural photosynthesis

Although a number of solar biohydrogen systems employing photosystem I (PSI) have been developed, few attain the electron transfer throughput of oxygenic photosynthesis. We have optimized a biological/organic nanoconstruct that directly tethers FB, the terminal [4Fe-4S] cluster of PSI from Synechococcus sp. PCC 7002, to the distal [4Fe-4S] cluster of the [FeFe]-hydrogenase (H2ase) from Clostridium acetobutylicum. On illumination, the PSI–[FeFe]-H2ase nanoconstruct evolves H2 at a rate of 2,200 ± 460 μmol mg chlorophyll-1 h-1, which is equivalent to 105 ± 22 e-PSI-1 s-1. Cyanobacteria evolve O2 at a rate of approximately 400 μmol mg chlorophyll-1 h-1, which is equivalent to 47 e-PSI-1 s-1, given a PSI to photosystem II ratio of 1.8. The greater than twofold electron throughput by this hybrid biological/organic nanoconstruct over in vivo oxygenic photosynthesis validates the concept of tethering proteins through their redox cofactors to overcome diffusion-based rate limitations on electron transfer.