FIG 3 .

Reversibility of spent cell-free culture medium-mediated hydrogen and formate formation in bioelectrochemical reactors at −200 mV. Low background current consumption is observed in an N₂-CO₂ (80/20) atmosphere in SCM-amended (solid black line) and uninoculated medium (gray line) (1). Upon addition of 10% H₂, current is generated only in the presence of SCM (2), current returns to background after replacing the gas phase with N₂-CO₂ (3), current is generated upon addition of 100 mM formate only in the presence of SCM (4), and replacing the gas phase by H₂-CO₂ (80/20) further increases current generation by SCM (5). Current spikes between treatments are due to disconnection of the electrochemical reactors from the potentiostat during handling.