The electrical conductivity of a Geobacter-enriched biofilm anode fed with acetate medium was assessed using small gold electrode systems as substrate concentration was changed. At 1.86 A/m(2) of the steady-state current density, biofilm conductivity was stable at 0.48-0.51 mS/cm. This high biofilm conductivity was not changed at short-term starvation ( < 7 h). In comparison, biofilm conductivity significantly decreased down to 0.16 +/- 0.002 mS/cm after 4 d of long-term starvation (current density 0.03 +/- 0.01 A/m(2)). Biofilm conductivity, however, was recovered to 0.35 +/- 0.03 mS/cm after 25 mM acetate spiking in a few days. The decrease and increase of biofilm conductivity in response to substrate conditions for long-term starvation was consistently observed in three consecutive cycles. This dynamic biofilm conductivity indirectly indicates that catabolism of exoelectrogens (i.e., energy generation) is associated with biofilm conductivity.