Rhodoferax ferrireducens
Amber McFadden

Chemical batteries have become common in today’s culture, but they have limitations, such as toxicity and overall lifetime, that some researchers believe could be overcome by a bacterial battery. Rhodoferax ferrireducens is the most promising bacteria currently. It is capable of producing an electrical current from an oxidation and iron reduction is as follows:



The actual recovery of the electrons is a slow process so before this bacterium can be used commercially to produce energy from organic waste materials, it must be sped up. Despite the speed, the collection of electrons is quite efficient, up to 85%, because it can directly transfer electrons to the surface of the electrodes. Before R. ferrireducens, the collection of electrons ranged anywhere from 1% to 50% efficiency. See the figure below for a diagram of the fuel cell from http://www.scq.ubc.ca/?p=241.

R. ferrireducens break down sugars in the fuel cell by reducing a graphite anode. The fuel cell works by allowing electrons to move along a current with hydrogen cations traveling to cathode, and water forms at the cathode to complete the battery circuit. Fuel cells using these bacteria would be very environmentally friendly because it would consume waste, no toxins are produced because of the reaction, and no toxic media is required for the reaction to take place; economically, things that use batteries as a power source would have to be redesigned, as would the factories that manufacture them.

R. ferrireducens was isolated from a coastal aquifer sediment sample in Oyster Bay, Virginia. It is a Gram-negative organism. The bacterium shape is a short rod and is 3-5µm long and 1µm wide. It has one polar flagellum, which allows for movement. The colonies are glossy white, smooth, round, and convex. Optimal growth occurs at 25°C and a pH of 7.0. This bacterium is tolerant of cold temperatures, however; growth and reduction can occur as low as 4°C. It has no fermentative or phototrophic growth. It is facultatively anaerobic and respires with Fe(III)-NTA, Mn(IV) oxide, fumarate, nitrate, and atmospheric oxygen. Electron donors that can be utilized are acetate, lactate, malate, propionate, pyruvate, benzoate, and succinate. PHA inclusion bodies form and they fluoresce under UV light when stained with Nile blue A. See below for micrographs of R. ferrireducens alone and of R. ferrireducens attached to a graphite electrode.


Image from: http://ijs.sgmjournals.org/cgi/reprint/53/3/669


Image from http://www.genomenewsnetwork.org/articles/09_03/battery.shtml
Scanning electron micrograph of Rhodoferax ferrireducens attached to a graphite electrode.
Image courtesy Derek R. Lovley/UMASS Amherst.

References

http://www.scq.ubc.ca/?p=241.

http://ijs.sgmjournals.org/cgi/reprint/53/3/669

ttp://www.genomenewsnetwork.org/articles/09_03/battery.shtml

*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.

 

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