Long-distance electron transfer by G. sulfurreducens biofilms results in accumulation of reduced c-type cytochromes

So close, but yet so far: G. sulfurreducens c-type cytochromes become reduced as biofilms grow on electrodes beyond a few cell thicknesses, even if the electrode is poised well above the potential required to oxidize all cytochromes. Cytochrome redox state also lags behind rapid potential changes during voltammetry, but only when the films are multiple cell layers thick, as would be expected if diffusional or exchange-based kinetics controls electron transfer between cytochromes.