Geobacter Research - Microbial Nanowires

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Microbial Nanowires

They’ve Got the Power: Microbes Produce Nanoscale Wires

UMASS-Amherst researchers report in the June 23, 2005 issue of Nature that Geobacter produces pilin-like filaments that function as nanowires to transfer electrons outside the cell onto insoluble electron acceptors, such as iron minerals and possibly electrodes. The filaments, which are only 3-5 nanometers in width (more than 10,000 times finer than a human hair), can extend more than 20 micrometers in length (more than 10 times the length of the cell). Elucidation of this novel form of electron transfer provides insight into the mechanisms by which Geobacter can contribute to bioremediation of groundwater contaminated with organic and metal contaminants. The potential to biologically mass-produce fine, long conductive filaments may have applications in the development of nanoelectronic devices, sensors, and microbially based fuel cells.

Links

UMASS press release [ .doc | .pdf ]
Read the article in Nature [ .pdf ]

[full-size image TIFF 242KB \| JPG 180KB] The structural subunits of the Geobacter’s pili, termed GEOPILINS, form an independent line of descent when compared to other bacterial pilins and the phylogenetically-related pseudopilins.	[full-size image TIFF 411KB \| JPG 81KB] Schematic representation of the components of an atomic force microscope (AFM).
[full-size image TIFF 163KB \| JPG 99KB] Schematic of the electronic connection of the AFM tip in a conducting probe atomic force microscope (CP-AFM). HOPG, highly oriented pyrolytic graphite.	[full-size image TIFF 838KB \| JPG 169KB] CP-AFM analyses of Geobacter sulfurreducens pili (arrows) demonstrating they are highly conductive. Left panel, topographic image generated by AFM. Middle panel, current image of the image shown on the left generated after applying a sweep-bias voltage (right panel) to the AFM tip while scanning.
[full-size image TIFF 272KB \| JPG 174KB] Top panel, topography and current overlaid image showing a pilus filament as well as other more globular outer membrane proteins sheared off the outer surface of G. sulfurreducens. Bottom panels, height and current values for cross sections “d1” and “d2” showing the current signal associated with the pilus. The other proteins lack conductivity (d1) and insulate the pilus from the conducting AFM tip (d2).	[full-size image TIFF 316KB \| JPG 76KB] CP-AFM analyses resulting from disabling the slow axis to repeatedly scan horizontally across the same portion of a pilus filament.
[full-size image TIFF 97KB \| JPG 64KB] Correspondence between pilus current and applied voltage demonstrating the linear, ohmic, response characteristic of a true conductor.	[full-size image TIFF 2.2MB \| JPG 112KB] Geopilin 3D-structure compared to the pilin of Pseudomonas aeruginosa strain K.

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Fe(III) oxides (black precipitates) preferentially associate with Geobacter sulfurreducens pili.

Photo credit: Gemma Reguera

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Geobacter sulfurreducens cells expressing pili (arrows).

Photo credit: Gemma Reguera and Dale Callaham

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Complementation of a pilin (pilA)-deficient mutant of Geobacter sulfurreducens with the wild-type pilA gene produces a hyperpiliated strain. Arrows point at pili.

Photo credit: Gemma Reguera.

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Geobacter sulfurreducens cells expressing pili.

Photo credit: Gemma Reguera and Dale Callaham

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Cells of Geobacter sulfurreducens grown with Fe(III) oxides. Arrows point at pili, which often are associated with the Fe(III) oxide particles (black precipitates).

Photo credit: Gemma Reguera

[full-size image TIFF 1.1MB | JPG 302KB]

Fe(III) oxides (black precipitates) preferentially associate with Geobacter sulfurreducens pili (arrows).

Photo credit: Gemma Reguera

[full-size image TIFF 1.0 MB | JPG 315KB]

Geobacter sulfurreducens cells expressing pili (arrows).

Photo credit: Gemma Reguera

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UMass researchers Gemma Reguera (right) and Kevin D. McCarthy used an atomic force microscope to study the conductive properties of Geobacter sulfurreducens pili.

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UMass microbiologists Derek R. Lovley and Gemma Reguera teamed with UMass physicists Mark T. Tuominen and Kevin D. McCarthy to study the conductive properties of Geobacter sulfurreducens pili. They found the pili were highly conductive. From left to right, Mark T. Tuominen, Derek R. Lovley, Kevin D. McCarthy and Gemma Reguera.

[full-size image TIFF 242KB \| JPG 180KB] The structural subunits of the Geobacter’s pili, termed GEOPILINS, form an independent line of descent when compared to other bacterial pilins and the phylogenetically-related pseudopilins.	[full-size image TIFF 411KB \| JPG 81KB] Schematic representation of the components of an atomic force microscope (AFM).
[full-size image TIFF 163KB \| JPG 99KB] Schematic of the electronic connection of the AFM tip in a conducting probe atomic force microscope (CP-AFM). HOPG, highly oriented pyrolytic graphite.	[full-size image TIFF 838KB \| JPG 169KB] CP-AFM analyses of Geobacter sulfurreducens pili (arrows) demonstrating they are highly conductive. Left panel, topographic image generated by AFM. Middle panel, current image of the image shown on the left generated after applying a sweep-bias voltage (right panel) to the AFM tip while scanning.
[full-size image TIFF 272KB \| JPG 174KB] Top panel, topography and current overlaid image showing a pilus filament as well as other more globular outer membrane proteins sheared off the outer surface of G. sulfurreducens. Bottom panels, height and current values for cross sections “d1” and “d2” showing the current signal associated with the pilus. The other proteins lack conductivity (d1) and insulate the pilus from the conducting AFM tip (d2).	[full-size image TIFF 316KB \| JPG 76KB] CP-AFM analyses resulting from disabling the slow axis to repeatedly scan horizontally across the same portion of a pilus filament.
[full-size image TIFF 97KB \| JPG 64KB] Correspondence between pilus current and applied voltage demonstrating the linear, ohmic, response characteristic of a true conductor.	[full-size image TIFF 2.2MB \| JPG 112KB] Geopilin 3D-structure compared to the pilin of Pseudomonas aeruginosa strain K.