Sources of non-Arrhenius electron transport in bacterial nanowires

Electron transport in biological redox chains typically follows an Arrhenius law, with rates and conductivities that increase with temperature. Surprisingly, bacterial nanowires show anti-Arrhenius transport. We simulated electron transport in a one-dimensional OmcS nanowire model from 275 K to 375 K using continuum electrostatic analysis of structural snapshots drawn from classical molecular dynamics simulations. We found that the electron-transport rate increases with temperature from 300-375 K, but more slowly than an Arrhenius law predicts. This softened temperature dependence is attributed primarily to temperature-dependence of the reaction free energies. Protein electrostatic interactions contribute to the weakened temperature dependence, but the effects are not large enough to invert the temperature dependence. The origins of anti-Arrhenius conduction is likely rooted in structural and dynamical factors beyond our model, including configuration-specific solvent interactions and entropy effects missing from the implicit-solvent treatment, as well as multidimensional transport pathways that may arise in bundled, cross-linked, or biofilm-embedded nanowire networks.