FIGURE 1.

Electrodes for enriching novel metal reducers from the terrestrial deep subsurface. (A) Map showing the location of the Soudan Underground Iron Mine within Minnesota’s Vermilion Range, approximately 30 km WSW of the town of Ely. (B) Photograph of diamond drill hole (DDH) 944 located along the west tunnel of Level 27 (713 m depth below the surface). A white precipitate is visible coating the platinized carbon cathode. (C) Schematic diagram of the electrode apparatus used for in situ enrichment. (D) Chronoamperometry of a potentiostatically controlled laboratory bioreactor (12 cm² total anode surface area) inoculated with the anode from the in situ enrichment. Red arrows indicate addition of acetate following substrate depletion.