Electrocatalytic oxidation of K₄[Fe(CN)₆] by metal-reducing bacteriumShewanella oneidensis MR-1

The microbial metabolic activities between metals and bacteria play a vital role on biogeochemical cycling of metal compounds. One of these activities is extracellular electron transfer (EET), in which some microbes exchange electrons with external redox minerals, electrodes, or even other microorganisms. The bacteria can either take electrons or give electrons. Shewanella oneidensis MR-1 (MR-1) is electrochemical active, it can transfer electrons from cell to extracellular electron acceptors including Fe(III) (hydro)oxides. In this study, we report that MR-1 electrocatalyze the oxidation of an inorganic redox compound K₄[Fe(CN)₆]. A pair of symmetric peak in the cyclic voltammetry (CV) of K₄[Fe(CN)₆] were found on bare glassy carbon electrode (GCE). Surprisingly, when the GCE is coated MR-1, the anodic peak almost sustained at the same level; while the cathodic peak apparently shrunk. We attribute this phenomenon to the electrocatalytic oxidation by MR-1. The discovery of the ability to oxidize [Fe(CN)6]^4- by MR-1 broadens our horizon of the role that dissimilatory metal reduction bacteria play in the environment.