BIMM130
Dr. Milton Saier
Bioelectricity via Nanowires
(Bug Juice)
Most bacteria use soluble electron acceptors for respiration, but some use insoluble, extracellular
electron acceptors. There are multiple mechanisms. One such mechanism uses nanowires that
conduct electrons to insoluble iron oxides (rust; Fe2O3) which the bacteria reduce to magnetite
(Fe3O4), a magnetic substance found in nature and in cells (including ancient bacterial fossils
billions of years old from both the Earth and Mars).
Bacteria that have been shown to use nanowires (unusual type IV pili; most type IV pili don’t
conduct) to transmit electrons to extracellular Fe2O3 and MnO4 include: Geobacter
sulfurreducens (a -proteobacterium), Schewanella (a -proteobacterium), Synechococcus (a
cyanobacterium), Pelomaulum (a thermophilic firmicute);  widespread.
Geobacter sulfurreducens was discovered by Derek R. Lovley in 1987 at the University of
Massachusetts, Amherst. It is a strict anaerobe that respires using extracellular electron
acceptors via nanowires (type IV pili). Electrons have been proposed to be passed through a
chain of e- carriers (mostly cytochrome c’s and multicopper proteins) as follows:
NADH  NADH DH  Menaquinone (MQ)  MacA (IM)  PpcA (periplasm) 
OmcB (OM)  OmcE (outer surface of OM)  OmcS (outer surface of OM)  pili  Fe2O3.
Derek Lovley and Ken Nealson (USC) created the fields of Geomicrobiology,
Bionanotechnology and Microbiological electronics as a result of their discoveries of
extracellular electron flow.
Geobacter oxidizes organic molecules to reduce external substances. Biofilms conduct
electricity to external Fe2O3 more efficiently than cell suspensions.
Targets of e- flow in Geobacter:
1. Iron ores  reduction
2. Other bacteria (same and different species; intra and interspecies energy exchange) 
energization.
3. Electrodes  bioelectricity
4. Fuel cells  stored electricity
5. Mini-power grids  long distance transport
6. Radioactive and other metals (e.g., soluble uranium (UVI)  insoluble uranium (UIV))
Electron donors:
1. Acetate
2. Oil
3. Organic toxins
BIMM130
Dr. Milton Saier
Uses:
1. They are used for bioremediation, esp. of ground waters (toxins, oils, heavy metals,
radioactivity, etc.)
2. They can convert animal wastes into electricity (used to light lamps).
3. Their pili can be harvested for e- conduction (nanowires).
4. Mutant pili (with subunits called pilins; ~3-5 nm in diameter, ~10  long) have different
useful properties for biotechnology.
References
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Hill, E.A., Shi, L., Elias, D.A., Kennedy, D.W., Pinchuk, G., Watanabe, K., Ishii, S., Logan, B.,
Nealson, K.H., and Fredrickson, J.K. (2006). Electrically conductive bacterial nanowires
produced by Shewanella oneidensis strain MR-1 and other microorganisms. Proc. Natl. Acad.
Sci. USA 103: 11358–11363.
Jones, S. (2006). Microbial physiology: new electricigens get wired. Nature Rev. Microbiol. 4:
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Heterologous expression of dodecaheme “nanowires” cytochromes c from Geobacter
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