Metabolic engineering of cyanobacteria for the production of hydrogen from water

Abstract

Requirements concerning the construction of a minimal photosynthetic design cell with direct coupling of water-splitting photosynthesis and H2 production are discussed in the present paper. Starting from a cyanobacterial model cell, Synechocystis PCC 6803, potentials and possible limitations are outlined and realization strategies are presented. In extension, the limits of efficiency of all major biological components can be approached in a semi-artificial system consisting of two electrochemically coupled half-cells without the physiological constraints of a living cell.

1 Cyanobacterial design cell for the production of hydrogen from water

“…high energy compounds, which are energetically and economically highly attractive: The classical route of energy storage via carbon compounds is extremely inefficient, ranging in most cases (due to metabolic constrains) from below 1 % and only in exceptional cases up to about 5 % efficiency , which is in contrast to the high efficiency of the primary (light-) reactions of photosynthesis [2,3]. For this reason, biofuel production has to be coupled as closely as possible to the light reactions of photosynthesis, combined with a re-routing of electrons which minimizes the steps of biofuel production and also the loss of electrons due to carbon fixation [4][5][6]. The attractive overall strategy is to receive the required electrons from the most abundant and cheapest compound available on earth -water -and to transfer them directly to the biofuel.…”

“…The competition of FNR and hydrogenase for the electrons from the linear photosynthetic electron transport chain [23][24][25] delivered by Fd is dominated by the following parameters: -the affinity of Fd for FNR is routinely higher by a factor of 10-40 than for [FeFe]-hydrogenase [4,26]; -the cellular amount of FNR will most probably exceed the amount of expressible (heterologous) hydrogenase considerably [20]; -the amount of functional hydrogenase will be reduced due to the inherent oxygen-sensitivity of the enzyme (for details see chapters 3, 4 and 5).…”

“…In conclusion, recent substantial progress in the elucidation of oxygen sensitivity on the molecular level, combined with improved knowledge on maturation and electron transfer design from PS1, yields a realistic chance for engineered integration of H 2 ase in a design cell for watersplitting-based hydrogen production [4].…”

Cyanobacterial Hydrogenases and Hydrogen Metabolism Revisited: Recent Progress and Future Prospects

“…Depending on their physiology and structure, the different divisions of cyanobacteria are known to evolve hydrogen through different mechanisms [24,25,26,27]. For most unicellular, non-heterocystous and filamentous cyanobacteria, nitrogen fixation and photosynthesis occur in the same cell.…”

“…Cyanobacteria primarily possess three enzymes related to hydrogen production including the bidirectional Hox enzyme that catalyzes both hydrogen oxidation and proton reduction; the nitrogenase enzyme complex that produces hydrogen as a byproduct of nitrogen fixation, and the uptake hydrogenase that functions to oxidize hydrogen and is found closely associated with the nitrogenase complex [24,25,26,27,32]. The precise physiological role of the bidirectional Hox enzyme is still under debate.…”