C-type cytochromes wire electricity-producing bacteria to electrodes

JUAN PABLO BUSALMEN; ESTEVE NUÑEZ, ABRAHAM; BERNÁ GALIANO, ANTONIO; MIGUEL FELIU, JUAN

ANGEWANDTE CHEMIE

Wiley-VCH

Año: 2008 vol. 47 p. 4874 - 4877

0570-0833

A new form of green energy based on the efficient conversion of organic matter into electricity is now feasible using microbial fuel cells (MFCs).[1] In these devices, microorganisms support theirgrowth by oxidizing organic compounds and an electrode serves as the sole electron acceptor, so electricity can be harvested.[2–4] Most of these electricity-producing microorganisms are FeIII-reducing bacteria.[5,6] Among them, the genus Geobacter is being extensively studied because of its outstanding electrogenic capacity.[7–11] Nevertheless, present understanding of the electron-transport mechanism and the specific interactions between bacteria and the electron accepting electrode are far from complete. By using a combined approach that includes direct current (DC) electrochemistry, surface enhanced infrared absorption spectroscopy (SEIRAS), and subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS), we have analyzed in vivo the intimate contact interface between the electricity-producing bacteria Geobacter sulfurreducens and a gold electrode at the nanometer scale. We show herein that upon potential cycling, reversible changes in the spectra produce a band pattern that clearly resembles the electrochemical turnover of oxidized/reduced states in c-type cytochromes. The unique presence of these signals associated to the cell/electrode interface demonstrates that outermost membrane cytochromes in Geobacter sulfurreducens are responsible for the direct electron transfer to electrodes during electricity production.