Figure 5. Model of the mutualistic relationship between E. coli and S. oneidensis.

Glucose is fermented by E. coli to yield metabolites such as formate, which is taken up by S. oneidensis as electron donor. Flavin mediator molecules are secreted to facilitate electron movement to the external charge collecting electrode to derive energy in MFCs. Flavins can also be taken up by E. coli to facilitate its respiration on electrodes as E. coli does not secrete flavins.