1. Department of Microbiology and
2. Department of Physics, University of Massachusetts, Amherst, Massachusetts 01003, USA
3. *These authors contributed equally to this work

Correspondence to: Derek R. Lovley¹ Correspondence and requests for materials should be addressed to D.R.L. (Email: dlovley@microbio.umass.edu).

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 sediments^{1, 2}. Previous investigations on electron transfer to Fe(iii) have focused on the role of outer-membrane c-type cytochromes^{1, 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 proposed^{1, 2}, on the basis of the role of pili in other organisms^{7, 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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