Biofilm sectional images and average RR spectra collected from electroactive biofilm at day 57 since inoculation under nonturnover conditions, with the electrode poised at 0(A, B, C, and D) or at −0.6 V (E, F, G, and H).

<p>Sectional maps (A, B, E, and F) are generated by binning the whole spectral information at 750 cm⁻¹ (A and E), and at 1641 cm⁻¹ (B and F), used here as markers of reduced and oxidized cytochromes, respectively. Each spectrum was averaged within the areas indicated by the dotted lines, representative of three biofilm locations, that is, top, middle, and bottom, respectively at a distance of 65, 40, and 15 µm from the electrode surface (not visible at the bottom of the spectral maps). The biofilm was exposed to the respective potentials for a period of at least 20 minutes to allow complete oxidation or reduction of cyt <i>c</i>, as suggested by stabilization of the current profile to very low levels (profiles shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0089918#pone.0089918.s003" target="_blank">Figure S2A and B</a>).