Modifying the endogenous electron fluxes of Rhodobacter sphaeroides 2.4.1 for improved electricity generation

• The iron chelating compound ferric nitrilotriacetic acid (Fe–NTA), that naturally exists in the SIS growth medium, mediates electron transfer between R. sphaeroides and electrode.
• The R. sphaeroides culture showed a light responsive electrochemical activity during chronoamperometry experiment, which is related to the intracellular quinone activity.
• The bioelectricity generation of R. sphaeroides was enhanced by genetic modification that alter the electron flows that are mediated by the cytoplasmic quinone pool

The purple bacteria Rhodobacter sphaeroides serve as a promising biocatalyst in the photo-microbial fuel cell system (photo-MFC). This gram-negative species performs highly efficient anoxygenic photosynthesis that ensures an anaerobic environment in the anode compartment. Previous studies incorporating R. sphaeroides into photo-MFC were conducted using platinum as the anode electrode. In this study, we detected a steady current generation of R. sphaeroides in a bioelectrochemical system where glassy carbon was the working electrode and a typical growth medium was the electrolyte. The bioelectricity generation synchronized with the supplementation of reduced carbon source and showed immediate response to illumination, which strongly indicated the correlation between the observed current and the cytoplasmic quinone activity. Modifications of the endogenous electron flows mediated by quinone pool are shown to have significantly enhanced the bioelectricity generation. We anticipate that the findings in this study would advance future optimization of R. sphaeroides as an anode strain, as well as facilitate the study of bioenergetics in photosynthetic bacteria.