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Johanna Wiedener (University Leipzig)

Schematic illustration of a mixed species approach of Synechocystis sp. PCC 6803 (Syn6803) and a heterotrophic aerobic bacterium to remove oxygen from the reaction to enable hydrogen production by the cyanobacterium (top) and co-cultivation as a biofilm in a capillary reactor (bottom). Graphic and photo: Johanna Wiedener

Johanna Wiedener's Master thesis was awarded with the Prize for the Best Plant Science Master Thesis, which was carried out at Leipzig University in the year 2020.

Title: Investigation of a mixed species cultivation concept for a continuous photosynthesis-driven hydrogen production

A mixed species cultivation using a photosynthetic cyanobacterium and an oxygen consuming heterotrophic bacterium enables light-driven and continuous hydrogen production from water.

Hydrogen is considered as the energy carrier of the future. In addition to a technical generation of hydrogen by electrolysis of water using renewable energies (solar/wind power), biological approaches are also possible. Promising are cyanobacteria, which also can split water by the means of light to ‘’win’’ electrons for biosynthesis. This process is known as oxygenic photosynthesis. In cyanobacteria the electrons obtained from water splitting can alternatively "flow" into the enzymatic synthesis of hydrogen.

The present work deals with the light-driven hydrogen production of the model strain Synechocystis sp. PCC 6803 – particularly to the dilemma that the hydrogenases necessary for hydrogen production, obtain electrons from photosynthesis but are at the same time inactivated by the oxygen also generated during photosynthesis. In this master thesis, the milieu was kept anaerobic for the first time by co-cultivating Synechocystis with a heterotrophic bacterium. Thereby a hydrogen synthesis was achieved that could be measured over several hours. It could be proven that the electrons for hydrogen synthesis indeed originate from photosynthetic water splitting. Furthermore, the observations could also be transferred to an alternative cultivation concept: a bacterial biofilm. 'Multi-species' biofilms represent the natural lifestyle of microorganisms and offer the advantage of improved tolerance to unfavorable environmental conditions. From a technical point of view, they allow a long-term, stable cultivation of microorganisms. If sufficient nutrient sources are present, they can generate all their needed elements by themselves and are also able of self-regeneration. In biofilms a significant hydrogen production was documented even after several weeks. It was proven that it is in fact the cyanobacterial partner that produces this hydrogen. Although many problems still need to be solved, this work has taken the biological approach of hydrogen production a significant step towards application.


Johanna Wiedener conducted this work at the Helmholtz-Centre for Environmental Research (UFZ) Leipzig in the department Solar Materials of Prof. Andreas Schmid under supervision of PD Dr. Stephan Klähn.