VISION: REGENERATIVE, C-FREE ENERGY  (zur Zeit nur in englisch verfügbar)

Conversion of Solar to Fuels neu-1

Hydrogen (H2) is considered the most promising energy carrier of the future. In combination with fuel cells, its reaction with oxygen produces environmentallly acceptable energy with water as the only by-product. While H2-based te(Dir H2, i.e. sources independent of fossil fuels, are still lacking. The aim of our project is the production of H2 from water as source of electrons and sunlight as continuous source of free energy. This principle is guided by the idea that a cycle of water is the most effective and the least polluting cycle of any substance on earth.

   MAJOR AIMS OF THE PROJECT

Major aim is the combination of the natural process of photosynthesis - which extracts electrons most efficiently from water by solar energy - with the reduction of protons by the enzyme Hydrogenase (H2ase). Both processes occur in nature in cells of cyanobacteria and green algae, but they have never been optimally synchronized for a most efficient H2 production. Major aims are:

A) Construction of a cyanobacterium-based „design cell“ which uses electrons from watersplitting photosynthesis primarily for H2 production instead for CO2-fixation (bioenergy instead of biomass production)

B) Development of low-priced photobioreactors, suitable for scale up and mass production


Features of the design cell:

  • Based on mutants of Synechocystis
     
  • PCC 6803Present H2-production per L cell culture
    (± 2 ml H2 L-1 h-1) has to be increased by a factor ≥100
     
  • Continuous H2-production under aerobic conditions (massfermentation)

   STRATEGY


The development of a H2-producing system should proceed on 3 levels:

  1. On the level of individual proteins (example: Design of O2-tolerant hydrogenase)

  2. On the cellular level (example: Re-routing of photosynthetic electron flow)

  3. On the mass cultivation level (example: Design of flat panel reactors for optimal light input)
 

   CHALLENGES OF THE PROJECT – MAJOR TASKS

Engineering of the cell metabolism

A) H2ase towards O2-tolerance:

Due to the high sensitivity of almost all H2ases against oxygen, which contradicts a highly efficient direct coupling with water-splitting photosynthesis, strategies have to be developed to overcome this problem

Method:

  • Directed and random mutations

  • Directed evolution in combination with high throughput screening

  • Comparison with O2-tolerant H2ases

B) PS-e-transport towards the highest possible efficiency from H2O to H2

 "Bio-energy cell"instead of "Bio-mass cell“


Maximization of linear electron flow from water-splitting PS2 to H2-producing hydrogenase by - for instance - increasing the PS2/PS1-ratio, increasing affinity of Fd for (heterologous) H 2 ase and decreasing affinity for FNR (i.e. CO2-fixation). Alternatively, fusion proteins of PS1 with various hydrogenases can be installed. Each step of this iterative improvement process is monitored on the cellular level for performance, viability and metabolic response.

C) Continuous photobioreactors:

towards maximal H2 production at minimal costs

Optimization of photobioreactor design (example: 5 L flat panel reactor, coop. KSD company, Hattingen) including efficiency evaluation of the whole system and its environment from a technical point of view


   PROOF OF PRINCIPLE BY SEMI-ARTIFICIAL MODEL SYSTEMS („BIOBATTERY“)




Semiartificial systems allow the separation of the O2-producing part, PS2, from the H2-producing, oxygen-sensitive part, H2ase, by immobilizing them on separate electrodes in separate compartments. In such a system ("biobattery"), all components can be exchanged and tested for optimal interaction by measuring light-triggered photo-currents from the water-splitting site (left) to the H2-producing site (right). Therefore, this model system can be used both as blue print for the design of most efficient natural systems or completely artificial modules.

   OUTLOOK

This figure summarizes the "biological" strategy of this project and its future application: Engineered algal cells produce (bio-) hydrogen from water using sun energy (in parallel, CO2 of the air is transformed into biomass). H2 reacts with oxygen in a fuel cell and produces energy. The "waste" product of this reaction is water, which closes the circuit of H2, water and energy.

   REVIEWS

Lubitz, W.; Reijerse, E. J.; Messinger, J. (2008)
Solar Water-Splitting into H2 and O2: Design Principles of Photosystem II and Hydrogenases.
Energy Environ. Sci., 1, 15-31.pdf

Esper, B., Badura, A. & Rögner, M. (2006)
Photosynthesis as a power supply for (bio-)hydrogen production;
Trends in Plant Sci. Vol. 11, No. 11

Waschewski, N., Bernat, G. & Rögner, M. (2010)
Engineering photosynthesis for H2 production from H2O: Cyanobacteria as design organisms in: "Biomass to Biofuels – Strategies for Global Industries" (Vertes, A., Qureshi, N., Yukawa, H., Blaschek, H.P. eds.) John Wiley & Sons, Chichester, UK, p. 387-401