Solar powered microbial fuel cell (photo-MFC) is a potential candidate for harnessing solar energy as a clean and environmental-friendly energy source. In a conventional MFC, the generation of bioelectricity can be achieved by using microorganisms in the anode as cheap and regenerative biocatalyst. By applying phototrophic inoculum, solar energy can be incorporated into central metabolism of anode microbes and contribute directly or indirectly to the bioelectricity generation. In the past decades, cyanobacteria arose most attention in the photo-MFC development owing to their remarkable light harvesting capability and self-sustainability by fixing atmospheric CO₂ into carbohydrate. However, it generates oxygen as a byproduct during photosynthesis, which scavenges electrons and se...[ Read more ]

Solar powered microbial fuel cell (photo-MFC) is a potential candidate for harnessing solar energy as a clean and environmental-friendly energy source. In a conventional MFC, the generation of bioelectricity can be achieved by using microorganisms in the anode as cheap and regenerative biocatalyst. By applying phototrophic inoculum, solar energy can be incorporated into central metabolism of anode microbes and contribute directly or indirectly to the bioelectricity generation. In the past decades, cyanobacteria arose most attention in the photo-MFC development owing to their remarkable light harvesting capability and self-sustainability by fixing atmospheric CO₂ into carbohydrate. However, it generates oxygen as a byproduct during photosynthesis, which scavenges electrons and severely reduces the current collected via external circuit.

Rhodobacter sphaeroides, a purple non-sulfur bacterium that performs highly efficient anoxygenic photosynthesis, could serve as a potential substitute for cyanobacteria in photo-MFC. The well-established culturing methods and genetic manipulation tools have paved ways for the study of R. sphaeroides as a model organism in bacterial photosynthesis. Moreover, this metabolic versatile species can grow by respiring a wide range of organic substrate, which holds a great promise in sustaining the electricity generation process in complex medium such as wastewater.

In this study, a steady current generation of wild type R. sphaeroides was observed during chronoamperometric measurement without involving the in-situ oxidation of hydrogen. Using glassy carbon as the anode and Sistrom’s minimal medium as the electrolyte in a three electrode system, the bioelectricity generation synchronized with the supplementation of reduced carbon source and showed instantaneous response to illumination. The result indicated that the genetic manipulation of endogenous electron transfer pathways in R. sphaeroides has significantly affected the bioelectricity output, which strongly argues a correlation between observed current and cytoplasmic Quinone pool (Q) -mediated electron chains. This study represents a pioneering work in utilizing genetic engineering tools for improving efficiency of a photo-MFC, which motivates further investigations into anode strain optimization. It is also anticipated that the observed correlation between current output and electron chain manipulation would be of great interests for study of bioenergetics in photosynthetic bacteria.