FIG 1.

Methods for assessing the conductivity of microbial nanowires. (A) e-pilus assembled from G. metallireducens pilin bridging the 500-nm nonconducting gap between two electrodes in a nanoelectrode array (left) and a current-voltage plot (right) demonstrating ohmic-like conductivity of the pilus (G. met). (B) Atomic force microscope (AFM) image of pili from Syntrophus aciditrophicus (designated with white arrows) on a highly oriented pyrolytic graphite (HOPG) surface (left) and conductance measured between a conductive AFM tip contacting the upper surface of an individual pilus and the HOPG for individual pili from S. aciditrophicus, wild-type G. sulfurreducens, and the Aro-5 strain of S. aciditrophicus (right). (C) Transmission electron micrograph of a thin-film of G. sulfurreducens e-pili (left) and conductance across a 15-μm electrode-to-electrode gap of thin films of pili harvested from strains of G. sulfurreducens heterologously expressing the pilin monomer gene from the designated microbes (right). (D) Transmission electron micrograph demonstrating heterologous expression of a synthetic pilin gene in G. sulfurreducens (left). The wild-type pilin was modified with six histidines (His tag) at the carboxyl end, and the His tag on the pili was visualized with immunogold labeling. Current production of various strains of G. sulfurreducens heterologously expressing the pilin monomer gene from the designated microbes (right). The left image in panel C is unpublished data provided by our laboratory colleague Joy Ward. The remaining images were reproduced from previously published images with permission as follows: panel A, reference 4; panel B, reference 9; panel C, right, reference 7; panel D, left, reference 14; panel D, right, reference 7.