Excess Ferrous Iron Promotes the Construction of Extracellular Electron Pathways in the Iron-corroding Bacterium Desulfovibrio ferrophilus IS5

Microbial extracellular electron uptake (EEU) is central to bioelectrochemical processes and biocorrosion, yet its underlying mechanisms are not fully understood under microbially influenced iron corrosion. Here, we investigate how excess Fe2+ modulates EEU in Desulfovibrio ferrophilus IS5, a strain that causes severe anaerobic iron corrosion via outer-membrane cytochromes (OMCs)-mediated electron uptake. We show that IS5 grown with elevated Fe2+ exhibits substantially enhanced EEU. This enhancement arises through two complementary mechanisms: (i) increased abundance of functional OMCs via the upregulation of a cytochrome assembly protein, and (ii) an additional electron transfer route mediated by FeS nanoparticles precipitated on the IS5 outer membrane. This indicates that, during iron corrosion, when IS5 cells are found within thick layers of corrosion products and biofilms, they simultaneously utilize both OMCs and FeS nanoparticles to sustain high-rate EEU from iron under conditions of high Fe2+ concentrations and limited organic substrates. This study advances the mechanistic understanding of EEU-driven iron corrosion and highlights a potential avenue for manipulating bioelectrochemical systems.