Fig. 4.

Decrease in anabolic activity with distance from the electrode is already present in thin biofilms. (A–C) Current density (A) and transmission electron microscopy images (B and C) of representative G. sulfurreducens biofilms harvested during exponential phase. Graphite electrodes poised at +240 mV vs. SHE served as the terminal electron acceptor, and normal growth media were exchanged with stable isotope-labeled media after 35 h of growth (arrow in A). (D) Anabolic activity patterns in duplicate G. sulfurreducens biofilms. Red and purple lines represent the average ¹⁵N fractional abundance at different locations within a single biofilm (the numbers of acquisitions per biological replicate are shown in parentheses in the legend). Transparent envelopes surrounding lines represent the SD of fractional abundance at each distance. Black lines represent controls that were chemically fixed before incubating with isotopically labeled media. For comparison, data from A and D are overlaid on data in gray from Figs. 1A and 2D, respectively, to show the similar maximum and decrease with distance features.