The bacterium Shewanella Oneidensis belongs to the so-called exoelectrogenic bacteria. These can produce electrons in their metabolic process and transport them to the outside of the cell. They thus form a “bio-battery”. However, the attempt to make this electricity usable failed, because oft he limited interaction of the organisms with the electrode. In contrast to conventional batteries, the material of this biobattery must not only conduct the electrons to an electrode, but at the same time optimally connect as many bacteria as possible to the electrode.
Until now, however, conductive materials in which bacteria could be embedded were either inefficient or lacked the ability to control the electrical current. Professor Christof M. Niemeyer’s team has now succeeded in developing a nanocomposite material that supports the growth of exoelectrogenic bacteria and at the same time conducts the current in a controlled way.
“For this purpose, we have produced a porous hydrogel consisting of carbon nanotubes and silica nanoparticles. These are interwoven by DNA strands,” explains Niemeyer. The research group added the bacterium Shewanella oneidensis and a liquid culture medium to the scaffold. The combination of different materials and microbes worked: “The cultivation of Shewanella oneidensis in the conductive materials shows that the exoelectrogenic bacteria colonise the scaffold, while other bacteria only remain on the surface of the matrix,” explains microbiology professor Johannes Gescher.
In addition, the research team was able to show that the flow of electrons increased the more bacterial cells colonised the conductive, synthetic matrix. This biohybrid composite remained stable for several days and showed electrochemical activity, proof that the composite material is able to efficiently conduct the electrons produced by the bacteria to an electrode.
In order for such a system to be of practical use, it needs not only conductivity but also the ability to control the process. This was also successful in the experiment: In order to switch off the current, the researchers added an enzyme that cuts DNA strands, thereby breaking down the composite material.
“As far as we know, this is the first time such a complex and functional biohybrid material has ever been described. Overall, the results suggest that potential applications of such materials might even go beyond microbial biosensors, bioreactors and fuel cell systems,” emphasises Niemeyer.
The research team reports on its findings in the journal ACS Applied Materials & Interfaces (https://pubs.acs.org/doi/10.1021/acsami.9b22116)