A recently developed photosynthetic cathodic half cell has been coupled to a fermentative anode to produce a complete microbial fuel cell. The photosynthetic organism Chlorella vulgaris was employed as the electron acceptor in the cathodic half cell with the yeast strain Saccharomyces cerevisiae serving as the electron donor in the anodic half cell. Maximum power was observed at 90 mV and a load of 5000 Omega, giving a power density of 0.95 mW/m(2) of electrode surface area. The effect of changing culture conditions on fuel cell operation is reported. A maximum open circuit voltage of 315 mV was achieved with the addition of supplemental glucose to the anodic half cell. Enriching the feed air bubbled into the cathode half cell with 10% CO2 increased the open circuit voltage by a factor of 1.5 compared to using pure air as the feed gas. Since photosynthetic microbial growth at the cathode of the MFC consumes CO2, this complete microbial fuel cell is CO2 neutral and produces both electricity and ethanol as valuable energy products.