Electrochemical evidence for direct interspecies electron transfer between Geobacter sulfurreducens and Prosthecochloris aestuarii

The syntrophic photosynthesis via direct interspecies electron transfer (DIET) between Geobacter sulfurreducens and Prosthecochloris aestuarii has opened a new paradigm of microbial phototrophy. However, it is still unknown whether this photosynthetic DIET can be mediated by an electrical conductor. Here we report first the photosynthetic DIET in a two-chamber microbial fuel cell (photo-MFC). The photo-MFC worked well and generated a maximum current of 0.6 mA/m², which validated photosynthetic DIET via the titanium wire. Confocal laser scanning microscopy showed that G. sulfurreducens and P. aestuarii colonized the anode and cathode, respectively. P. aestuarii accepted extracellular electrons from G. sulfurreducens bioanodes under illumination at a current density of 0.6 mA/m² (normalized to the cathode surface area), which could not be produced in the dark. Such a light-dependent electron uptake from solid electrodes by P. aestuarii was closely related with the presence of CO₂, suggesting that P. aestuarii utilized extracellular electrons for photosynthetic CO₂ reduction. Electrochemical in situ Fourier transform infrared (FTIR) spectroscopy revealed that certain outer membrane components of the two strains were involved in the DIET process. These results implied photosynthetic DIET can be mediated by electrically conductive materials in natural environments.