Biosynthesized Iron Sulfide Nanocluster Enhanced Anodic Current Generation by Sulfate Reducing Bacteria in Microbial Fuel Cells

The anodic oxidation of sulfide metabolically generated from sulfate is considered to be the primary mechanism of sulfate reducing bacteria (SRB) to contribute to the current generation in Microbial Fuel Cells (MFCs). However, the other redox active metabolic by-product of conductive iron sulfide (FeS) has been seldomly studied in the context of anodic current generation. Here, we demonstrate that the biomineralized FeS increased the anodic current production in Desulfovibrio vulgaris Hilden-borough, compared with that mediated by diffusive sulfate. Chronoamperometry on indium tin-doped oxide electrodes (ITO) poised at 0.4 V (vs SHE) in the presence of lactate and sulfate showed that the presence of ferrous ion caused twice more anodic current than that in the absence of the iron. Linear Sweep Voltammetry (LSV), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy confirmed that the aggregation formation of cells with FeS and FeS2 particles on the surface of the ITO electrode. These iron sulfur precipitates were more oxidized on the anode surfaces once lactate was depleted as electron source. The presented data suggests that biosynthesized FeS mediates the electron transport from D. vulgaris Hilden-borough to the electrode surface. Given microbial capability of FeS biosynthesis is general among SRB, the FeS-mediated mechanism may dominate anodic current generation of SRB in MFCs.