User:Kbseah/Cable bacteria

Cable bacteria are filamentous bacteria living in aquatic sediments that are able to conduct electrical currents over several centimeters.

Electrical conduction
Many bacteria use the chemical oxidation of inorganic compounds, e.g. the oxidation of hydrogen sulfide with oxygen, to generate energy for their metabolism and growth. However, in the sediment habitat, oxygen and sulfide sources may not be overlapping: oxygen is typically consumed within the upper-most layers of aquatic sediment, whereas sulfide is produced by sulfate-reducing bacteria in the anoxic, deeper layers.

Cable bacteria are able to bridge the separation between the oxidant and reductant by carrying an electrical current, much like in an electrochemical cell. The electrochemical half-reactions are:


 * 1/2 O2 + 2 e- + 2 H+ → H2O (oxygen as electron acceptor)


 * H2S → S0 + 2 H+ + 2 e- (sulfide as electron donor)

Ecological significance
The discovery of cable bacteria helped to explain how the rates of oxygen consumption and sulfide consumption in aquatic sediment are often observed to be correlated even when those substances are spatially separated by several centimeters. Two of the scientists who were involved in the discovery related the following anecdote:"In the microbial ecology course at our department, we had for many years a laboratory exercise aiming at a complete mass balance for the cycling of carbon, sulfur, nitrogen, iron, and oxygen in three-week incubations of homogenized sediment collected from station M5 in Aarhus Bay. The oxygen budget never fit, and the poor students (and teachers) were blamed for bad performance or choice of methods. After reinspection of the data and repetitions with pH profiles included, it appears that electric currents were the only missing link."

Diversity
All known cable bacteria are members of the family Desulfobulbaceae, in the class Deltaproteobacteria. There are two candidate genera that have been proposed: Candidatus Electrothrix, which is specific to marine sediment habitats, and Candidatus Electronema, which is found in freshwater.
 * Discover Magazine blog post about cable bacteria
 * Original publication
 * Also found in freshwater sediments.
 * Review article.
 * Review comparing cable bacteria and direct interspecies electron transfer.
 * Can prevent release of sulfide by generating oxidized iron minerals in sediment, which bind to free sulfide.