In Vivo Assembly of Photosystem I‐Hydrogenase Chimera for In Vitro PhotoH₂ Production

Abstract

surplus of energy as photoH 2 at the onset of photosynthesis after a period of dark adaptation. However, this hydrogen is subsequently consumed again by the cells. The algal and cyanobacterial hydrogenases that catalyze the production and consumption of hydrogen are oxygen sensitive. As soon as photosynthesis operates at full capacity, molecular oxygen accumulates due to water splitting at photosystem II (PSII) and inactivates hydrogen production. The amount of photoH 2 that natural cyanobacteria and algae produce does not suffice for biotechnological approaches. Therefore, several strategies have been established to enhance and prolong in vivo photoH 2 production via genetic manipulations and modified culture conditions. [1] The most efficient and direct approach is to fuse the hydrogenase to PSI genetically. The light-induced charge separation in PSI unleashes an electron transfer pathway within PSI, which finally reduces the terminal 4Fe4S cluster F B . In natural cyanobacterial and algal strains, F B transfers electrons to the soluble electron carrier ferredoxin, which donates electrons to a plethora of metabolic reactions. The fusion of a hydrogenase to PSI aims to harness these low potential electrons from F B . This was recently accomplished in vivo in the green alga Chlamydomonas rheinhardtii and the cyanobacterium Synechocystis sp. PCC 6803. [2] Photosynthetic hydrogen (photoH 2 ) production is an elegant approach to storing solar energy. The most efficient strategy is to couple the hydrogenproducing enzyme, the hydrogenase (H 2 ase), directly to photosystem I (PSI), which is a light-driven nanomachine found in photosynthetic organisms. PSI-H 2 ase fusions have been tested in vivo and in vitro. Both approaches have each their specific advantages and drawbacks. Here, a system to combine both approaches by assembling PSI-H 2 ase fusions in vivo for in vitro photoH 2 production is established. For this, cyanobacterial PSI-H 2 ase fusion mutants are generated and characterized concerning photoH 2 production in vivo. The chimeric protein is purified and embedded in a redox polymer on an electrode where it successfully produces photoH 2 in vitro. The combina-

Making the connections: physical and electric interactions in biohybrid photosynthetic systems

“…Extracellular electron transfer (EET) is a process in which microorganisms transport electrons into and out of the cell from or towards an insoluble electron donor or acceptor. 38,121 The ability and efficiency of the organisms to exchange electrons with electrodes and more importantly to connect this EET to its original cellular metabolism is not only a crucial step in MFCs/MES but also a primary operational objective in the hybrid photosynthesis field. A more thorough understanding of possible EET pathways is needed to optimise and advance hybrid photosynthesis systems.…”

Rewiring photosynthetic electron transport chains for solar energy conversion

“…NADH oxidising enzymes have been engineered to bind NADPH instead, enhancing their activity in phototrophs 99 . Recent studies have engineered chimeric proteins where enzymes are directly fused to PETC components such as RCPs, greatly enhancing the redirection of electron flux [100][101][102][103][104][105] . Synthetic biology can also be used to engineer EET and EEU pathways (Fig.…”

Temperature modulated sustainable on/off photosynthesis switching of microalgae towards hydrogen evolution

“…In this regard, besides biotechnological strategies, [3][4][5][6] the recently developed technique of combining abiotic substances with living organisms has also been recognized as a feasible pathway for boosting photohydrogen production from solar energy, [7][8][9][10][11][12][13] which should then offer promising opportunities to solve the energy crisis and concurrent environmental problems. By taking algae as an example, various abiotic materials, including silicon dioxide, 14,15 gelatinizable protein, 16 catalytic enzyme, 17,18 conductive polymer and photosensitive nanoparticles, 19,20 have been successfully incorporated either onto the surface of or inside the algal cell, 21,22 and then the integrated materials could facilitate the generation of a mild hypoxic microenvironment, enabling the activation of intracellular hydrogenase to induce the functionality switching of algal cells from normal oxygen evolution to photosynthetic hydrogen production. For example, by forming a sandwich-like layer around a single algal cell, laccase-catalyzed oxygen-consuming reaction triggered hydrogen production was achieved at the rate of 0.32 mmol H 2 per h per mg chlorophyll for 7 days.…”