Bacterial Species Found to “Eat” Electricity: a New Fad Diet?

By on March 21, 2014

Researchers at Harvard University have discovered that a common bacterial species can use conductivity to draw electrons from vital minerals found deep in the soil.

Spearheaded by Peter Girguis, Associate professor of the natural sciences, and Arpita Bose, a post-doctoral fellow in the Organismic and Evolutionary Biology department, this study described Rhodopseudomonas palustris as able to attract electrons so that the bacterium can survive at the top of soil while flourishing off nutrients out of its reach.

Typically, a species like Rhodopseudomonas palustris needs sunlight to survive, because the bacteria relies on photosynthesis as a means of food and energy production. Sunlight strikes pigments within the cells, providing energy to move electrons to produce cellular fuel.

So, the bacteria need a supply of electrons to perpetuate their process of photosynthesis—otherwise, they will die.

Living near the surface of soil provides strategic access to sunlight, but to get those extra electrons requires the species to suck electrons from the minerals around them, which is typically iron. Other substances, such as sulfur or other non-ferrous metals, can also serve as the electron source.

A staple to the researchers’ paper is the idea of extracellular electron transport (EET), which describes the transfer of electrons in and out of cells.  The cells are essentially consuming electricity from the soil.

Giguis describes this finding as a “game-changer” because the traditional paradigm believes that organisms must rely on diffusion to be the interaction between the “aerobic and anaerobic worlds.”

That is, substances an organism needs to survive passively passes through its cell membrane because of difference between concentration gradients—a reason similar to why water in a waterfall travels towards the earth and not away from it. This bacterial species, however, does not necessarily have to rely on diffusion to produce food. Instead, it is able to attract electrons from iron and consequently produce iron oxide crystals, which eventually integrate to form makeshift circuits for the cells.

Using a genetic analysis, the scientists believe they have located a gene that exerts control over this extracellular electron transfer, and they decided to turn this gene off so that it wouldn’t perform its job; they found that the capacity to perform EET “dropped by a third.” Because this single gene and other related genes in other species, researchers are now interested in investigating other microbes that may have the same ability.

An interesting application for these bacteria is a fuel cell; while it may seem farfetched, harvesting the electricity these bacteria can produce may provide an alternative energy source.

A more likely application for this finding  is in the pharmaceutical industry, where they could potentially produce on-demand compounds by transferring electrons.

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