Electrode potential regulates cytochrome accumulation on Shewanella oneidensis cell surface and the consequence to bioelectrocatalytic current generation

This study investigated the physiological response of Shewanella oneidensis to the electrode potential and its effect on biological current generation. The electrode-attached S. oneidensis cells expressed cytochromes OmcA/MtrC at the bacteria-electrode interface when the electrode was poised at 0. V (vs. SCE), but not when the poised potential was -0.24. V. Cytochromes that had already been deposited on the interface were eliminated under -0.24. V. Unexpectedly, current density under the higher poised potential was very low, while the low current density was associated with accumulation of OmcA/MtrC at the Shewanella-electrode interface. Although OmcA/MtrC were widely believed to be electrode reductases, we found that their electrocatalytic activity was actually weak. An additional electron transfer pathway through diffusive electron shuttle flavins was more efficient. The electrocatalytically inactive OmcA/MtrC could probably insulate the electrode surface and hinder the contact between flavins and electrode, which inhibited current generation. The results highlighted that the bacterial exoelectrogenic physiology is directly relevant to the operation of bioelectrochemical systems.