Data for: Thermodynamic Controls on Rates of Iron Oxide Reduction by Extracellular Electron Shuttles

Anaerobic microbial respiration in sub- and anoxic environments often involves particulate ferric iron (oxyhydr-)oxides as terminal electron acceptors. To ensure efficient respiration, a widespread strategy among iron-reducing microorganisms is the use of extracellular electron shuttles (EES) that transfer two electrons from the microbial cell to the iron oxide surface. Yet, a fundamental understanding of how EES-oxide redox thermodynamics affect rates of iron oxide reduction remains elusive. Attempts to rationalize rates of iron oxide reduction for different EES, solution pH, and iron oxides on the basis of the underlying reaction free energy of the two-electron transfer were unsuccessful. Here, we demonstrate that reduction rates determined in this work for different iron oxides and EES under varying solution chemistry can be reconciled with existing rate data when instead related to the free energy of the less exergonic (or even endergonic) first of the two electron transfers from the fully, two electron-reduced EES to oxide ferric iron. We show how free energy relationships aid in identifying controls on microbial iron oxide reduction by EES and, thereby, advance a more fundamental understanding of anaerobic respiration using iron oxides.