Boundary of bioelectric induction in marine sediment. (A) Electric induction profiles of the cable bacteria (CB) layer at increasing depths. The data were collected from the negative signal at 7.2 ms and positive signal at 7.7 ms, detailed in the middle portion of Fig. 1C, as the depth increased. Each dataset was acquired at every 500-μm increase in depth. Error bars represent the variations in 3 replicate readings at each measured depth. (B) Electrostatic field in the sediment measured using an EP microsensor (38). The potentials read by this microsensor relative to an Ag/AgCl reference electrode in seawater were defined as the zero potential for the purpose of making comparisons between the EP values in sediment samples without (gray: control sample with no CB) and with CB (red). Each dataset was acquired at depths that increased in 100-μm increments. Error bars represent the standard deviations of triplicate measurements. (C) Oxygen, sulfide, and pH profiles produced by the CB. Error bars represent the standard deviations of triplicate measurements. Each dataset was acquired at depths that increased in 100-μm increments.