Fig. 2.
Overview of MFC processes and extracellular electron transport (EET) mechanisms. Indirect transport of electrons with shuttle transfer and direct transfer with surface contact is depicted in the left and middle sections of the figure. The electron shuttle mediates the indirect transfer of electrons back and forth between the electrode and bacterial cells. Where, Mtr (metal-reducing) conduit system comprising several multi-heme c-type cytochormes (c-Cyts) including Fcc3-flavocytochrome c3 (tetraheme), MtrA (periplasmic, decamehe), MtrB (outer membrane-bounded), CymA- (cytoplasmic inner membrane-bounded, tetraheme), STC-small tetra heme cytochrome, MtrC (periplasmic protein, decaheme) and OmcA-outer membrane c-Cyt (decaheme). MQ and OM represent menaquinol and organic matter, respectively. The sketch was drawn based on the information provided by Zou et al. [144].