Bacterial cell membranes iron species

Some microorganisms can directly transfer electrons to the electrode via a physical contact of the cell membrane or a membrane organelle with the anode. No diffusional redox species are involved in this electron transfer process. As illustrated in Figure 2.6a, the direct electron transfer requires the microorganisms to possess (1) membrane-bound protein relays which transfer electrons from the inside of the bacterial cell to its outside, and (2) an outer membrane (OM) redox protein which accepts the electrons and delivers them to an external, solid electron acceptor (a metal oxide or an MFC anode). The most studied OM redox proteins are c-type cytochromes, which are involved in metal-reducing microorganisms such as Geobacter, Rhodqferax and Shewanella. These bacteria often have to rely on solid terminal electron acceptors like iron(lll) oxides in their natural environments. 

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