In their search for sustainable ways to produce energy, researchers repeatedly use microorganisms or biomolecules extracted from them, such as certain photosynthesis proteins. “However, isolated molecules are generally not stable in the long term,” explains Dr. Felipe Conzuelo, a researcher from the university of Bochum. “One advantage of living cells is that they contain a “repair machine” to repair cell damage.” The system regenerates itself. However, one challenge when working with living organisms is that it is more difficult to get the electrons – i.e. ultimately the current – out of the cell and make them usable for a technical application. This is exactly what the team of researchers succeeded in doing.
Cyanobacteria have two systems for energy production in light and darkness. Light is photosynthesized using hydrogen and carbon dioxide to produce sugar molecules and oxygen. The process initiates an electron transport chain that drives the production of energy storage molecules such as ATP. In darkness, the stored sugar molecules are broken down again in the so-called cell respiration using oxygen to produce energy. Here too, electron transport plays a decisive role.
Using their cyanobacteria-coated graphite electrode, the researchers were able to derive electrons from both processes, photosynthesis and cell respiration, and thus generate a current flow outside the cell – more efficiently than in earlier systems. They found that a small soluble molecule exits the cells and transports the electrons to the electrode surface. However, this was only sufficiently successful if the group gently pretreated the cells before applying them to the electrode. For this purpose, the cells were pressed slightly so that the cell wall was no longer completely intact.
Unlike previous studies, the scientists did not have to add any molecules to their system for the uptake or release of electrons, but only used the substances contained in the natural cells. For the study, a team from the Israel Institute of Technology in Haifa and the Israeli Weizmann Institute cooperated with the Center for Electrochemistry at the Ruhr University Bochum.
“As far as we know, this is the first time that such a mediator molecule has been found, which comes from the living cells themselves, whose cell wall can pass through and transport electrons to the outside,” said Dr. Fangyuan Zhao from the Centre for Electrochemistry. Exactly which substance is involved is still unknown. However, the analyses showed that it must be a relatively small, water-soluble molecule that can pass through cell walls and membranes.
“We believe that the cyanobacteria system has the potential to become a green energy source,” sums up Prof. Dr. Wolfgang Schuhmann, head of the Bochum Chair of Analytical Chemistry. “With some modifications, it should be able to produce light-driven electricity over a long period of time – because it brings everything with it to regenerate itself again and again.”
The German-Israeli research team first published its results in the journal “Nature Communications” on 4 June 2018.