Photosynthesis as a power supply for (bio-)hydrogen production.

Although hydrogen is considered to be one of the most promising future energy sources and the technical aspects involved in using it have advanced considerably, the future supply of hydrogen from renewable sources is still unsolved. This review focuses on the production of hydrogen from water using biological catalysts that have been optimized by nature: the process of water-splitting photosynthesis on the one hand and hydrogen production via the catalyst hydrogenase on the other. Using water as a source of electrons and sunlight as a source of energy, both engineered natural systems and biomimetic (bio-inspired) model systems can be designed as first steps towards water-splitting-based hydrogen production (biophotolytic hydrogen production).

Light-driven water splitting for (bio-)hydrogen production: photosystem 2 as the central part of a bioelectrochemical device.

To establish a semiartificial device for (bio-)hydrogen production utilizing photosynthetic water oxidation, we report on the immobilization of a Photosystem 2 on electrode surfaces. For this purpose, an isolated Photosystem 2 with a genetically introduced His tag from the cyanobacterium Thermosynechococcus elongatus was attached onto gold electrodes modified with thiolates bearing terminal Ni(II)-nitrilotriacetic acid groups. Surface enhanced infrared absorption spectroscopy showed the binding kinetics of Photosystem 2, whereas surface plasmon resonance measurements allowed the amount of protein adsorbed to be quantified. On the basis of these data, the surface coverage was calculated to be 0.29 pmol protein cm(-2), which is in agreement with the formation of a monomolecular film on the electrode surface. Upon illumination, the generation of a photocurrent was observed with current densities of up to 14 microA cm(-2) . This photocurrent is clearly dependent on light quality showing an action spectrum similar to an isolated Photosystem 2. The achieved current densities are equivalent to the highest reported oxygen evolution activities in solution under comparable conditions.

Potassium uptake in the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 mainly depends on a Ktr-like system encoded by slr1509 (ntpJ).

The molecular basis of potassium uptake in cyanobacteria has not been elucidated. However, genes known from other bacteria to encode potassium transporters can be identified in the genome of Synechocystis sp. strain PCC 6803. Mutants defective in kdpA and ntpJ were generated and characterized to address the role of the Kdp and KtrAB systems in this strain. KtrAB is crucial for K(+) uptake, as the DeltantpJ mutant shows slowed growth, slowed potassium uptake kinetics, and increased salt sensitivity. The DeltakdpA mutant has the same phenotype as the wild type even at limiting potassium, but a DeltakdpADeltantpJ double mutant is not viable, indicating a role of Kdp for potassium uptake when the Ktr system is not functioning.