Electrode assisted production of platform chemicals in Rhodobacter sphaeroides.

The aim of this study was to establish cathodic biofilms of the photosynthetic non sulfur purple bacterium Rhodobacter sphaeroides as biocatalyst for the production of platform chemicals from carbon dioxide as carbon source and an electrical current as energy and electron source.  Therefore, R. sphaeroides was cultivated in a bioelectrical system (BES) in which light, CO₂ and a stable current were provided. Chronopotentiometric measurements revealed the cathode potential necessary to maintain the applied current of I = 22,2 µA/cm². Interestingly, exposure of R. sphaeroides to the antibiotic kanamycin lead to increased biofilm production on the cathode although the organism expressed the necessary resistance marker. This enhanced biofilm production raised the potential by 170 mV to E = -1 V compared to the wildtype (E = -1,17 V) and hence increased the efficiency of the process. To date, the molecular basis of this effect remains unclear and is under investigation using a proteomic approach. To elucidate, if the productivity of R. sphaeroides as a production strain is also enhanced, the production of acetoin was established as proof of principle. After the confirmation of the acetoin production under autotrophic conditions, various approaches to increase the space-time yields of the process were conducted and their effect will be presented.