Evidence for High Conductivity in the Pili of \textit{Geobacter sulfurreducens}: ``Nano-wires'' in a Prokaryotic Electron Transport Chain?*

We discuss results of Conducting-Probe Atomic Force Microscopy (CP-AFM) applied to the nanoscopic filamentary pili of the prokaryote \textit{Geobacter sulfurreducens.} (G. Reguera, et al., Nature \textbf{435}, 1038, 2005) The apparently high cross-axis conductivity of this bacterial membrane protein complex, along with evidence of its necessity for respiratory reduction of insoluble Fe(III) deposits in nature, points to the possibility of a novel role for the pili protein complex in the electron transport chain of a prokaryote: as a kind of ``nano-wire'' for conduction of electrons to Fe(III) oxides. CP-AFM and \textit{in vivo} genetic engineering experiments supporting the ``nano-wire'' hypothesis are presented.