Shewanella oneidensis MR-1 electron acceptor taxis and the perception of electrodes poised at oxidative potentials

Shewanella oneidensis MR-1 is a facultative anaerobe, capable of respiring on an extraordinarily large and diverse array of both intra- and extracellular terminal electron acceptors, including insoluble metal oxides and electrodes. The ability to perform extracellular electron transfer has sparked great interest over the last three decades and MR-1 has become both a model organism for fundamental research into extracellular electron transfer and a candidate microbe for microbial electrochemical systems, including microbial fuel cells. A pre-requisite for colonisation and biofilm formation on electrodes is the migration of bacteria towards the electrode. Here, we review current understanding in the steps involved in MR-1 migration towards insoluble electron acceptors and electrodes. The main experimental techniques used to evaluate taxis are summarised and different mechanisms proposed for MR-1 taxis are contrasted, in particular chemotaxis versus energy taxis.