On the low‐frequency electrical polarization of bacterial cells in sands

We performed electrical measurements on sands flushed with bacterial suspensions of varying concentration. The first experiment was conducted with Shewanella putrefaciens (biomass 0–0.5 mg/L) and the second with Escherichia coli (biomass 0–42 mg/L). We measured a biomass‐dependent low‐frequency (10 Hz) polarization. At cell density <12 mg/L polarization decreased (up to 60 %) relative to before introduction of cells; the decrease was greater when the sand was artificially Fe‐coated to enhance the affinity of cells to the mineral surface. At cell density >12 mg/L polarization increased (up to 15%). We attribute the decrease in polarization at low cell density to alteration of the mineral‐fluid interface due to mineral‐cell interactions. The polarization enhancement at higher cell density is possibly a pore throat mechanism resulting from decreased ionic mobility and/or electron transfer due to cell accumulation in pores.