Surface of living bacteria aids in direct electron transfer through use of network of nanofilaments (pili) that conduct electricity.

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It was previously accepted that the surface of cells used a protein (cytochromes) to aid in communication and electron transfer between cells. This recent study suggests, however, that cell communication can extend beyond just the surface with nanofilaments known as pili. These pili aid in cell diversity but also in the breakdown of important compounds such as Iron (III) oxide (Fe(III)). They provide a type of "bridge" across which electrons can travel between cells. As the electrons move, a current is produced and a type of conductor is created. This electrical charge provides the energy and electricity needed to break down such strong compounds.

This summary was contributed by Ashley Meyers

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"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. Previous investigations on electron transfer to Fe(III) have focused on the role of outer-membrane c-type cytochromes. However, some Fe(III) reducers lack c-cytochromes. Geobacter species, which are the predominant Fe(III) reducers in many environments, must directly contact Fe(III) oxides to reduce them, and produce monolateral pili that were proposed, on the basis of the role of pili in other organisms, 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. This indicates that G. sulfurreducens requires pili in order to reduce Fe(III) oxides because pili are the electrical connection between the cell and the surface of the Fe(III) oxides. This contrasts with the nearly universal concept that outer-membrane cytochromes are the proteins that transfer electrons to Fe(III) oxide in Fe(III) reducers. The conductive pili provide the opportunity to extend electron transfer capabilities well beyond the outer surface of the cells, which might be especially important in soils in which Fe(III) oxides exist as heterogeneously dispersed coatings on clays and other particulate matter." (Reguera et al. 2005.

Journal article
Extracellular electron transfer via microbial nanowiresNatureJune 22, 2005
Gemma Reguera, Kevin D. McCarthy, Teena Mehta, Julie S. Nicoll, Mark T. Tuominen, Derek R. Lovley


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