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Extracellular electron transfer via microbial nanowires

Abstract

Microbes that can transfer electrons to extracellular electron acceptors, such as Fe(iii) oxides, are important in organic matter degradation and nutrient cycling in soils and sediments1,2. Previous investigations on electron transfer to Fe(iii) have focused on the role of outer-membrane c-type cytochromes1,3. However, some Fe(iii) reducers lack c-cytochromes4. Geobacter species, which are the predominant Fe(iii) reducers in many environments1, must directly contact Fe(iii) oxides to reduce them5, and produce monolateral pili6 that were proposed1,2, on the basis of the role of pili in other organisms7,8, to aid in establishing contact with the Fe(iii) oxides. Here we report that a pilus-deficient mutant of Geobacter sulfurreducens could not reduce Fe(iii) oxides but could attach to them. Conducting-probe atomic force microscopy revealed that the pili were highly conductive. These results indicate that the pili of G. sulfurreducens might serve as biological nanowires, transferring electrons from the cell surface to the surface of Fe(iii) oxides. Electron transfer through pili indicates possibilities for other unique cell-surface and cell–cell interactions, and for bioengineering of novel conductive materials.

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Figure 1: Geobacter sulfurreducens pili.
Figure 2: Transmission electron microscopy analyses.
Figure 3: Effect of a mutation in pilin production on reduction of Fe( iii ) oxide and attachment.
Figure 4: Conducting-probe atomic force microscopy.

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Acknowledgements

We thank T. Russell and D. Bryant for helpful suggestions. This research was supported by grants to D.R.L. from the Department of Energy's Genomics:GTL and NABIR programmes and DARPA, by a grant to M.T.T. from the National Science Foundation, and by a postdoctoral fellowship to G.R. from the Ministerio de Educación y Ciencia of Spain.

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Correspondence to Derek R. Lovley.

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Supplementary information

Supplementary Methods

This file contains additional information on phylogenetic analyses, attachment assays, G.sulfurreducens pilT gene and twitching motility assays and pili preparation for CP-AFM (DOC 42 kb)

Supplementary Figures

This file contains Supplementary Figures S1-S5, with corresponding figure legends. (PPT 4527 kb)

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Reguera, G., McCarthy, K., Mehta, T. et al. Extracellular electron transfer via microbial nanowires. Nature 435, 1098–1101 (2005). https://doi.org/10.1038/nature03661

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