Shewanella oneidensis / U.S. Department of Energy
Janet Fang 18/07/2014, 20:52

When we eat, our cells break down sugars, while their excess electrons flow through a series of chemical reactions until they’re passed onto oxygen. This process generates the energy molecule ATP, vital to nearly all living things. "Life's very clever,” Kenneth Nealson from the University of Southern California says. "It figures out how to suck electrons out of everything we eat and keep them under control."  

Not too surprisingly then, there are bacteria out there that eat and excrete electrons -- and as it turns out, they’re everywhere. 

Years ago, researchers discovered two types of electric bacteria, Geobacter and Shewanella, which use energy in its naked, purest form: electrons harvested from the surface of rocks and minerals. Now, scientists show that many more electric bacteria can be fished out of rocks and marine mud by baiting them with a bit of electrical juice, New Scientist reports

"Electrons must flow in order for energy to be gained,” Nealson explains. “This is why when someone suffocates another person they are dead within minutes. You have stopped the supply of oxygen, so the electrons can no longer flow." 

Electric bacteria, however, have done away with sugary middlemen.

Nealson and colleagues have grown electric bacteria on battery electrodes, keeping them alive with electricity and nothing else. (In humans, that’d be like powering up by shoving our fingers in a socket.) The team collected seabed sediment and inserted electrodes inside of it. Applying a slightly higher voltage than the sediment’s natural voltage results in an excess of electrons -- which bacteria in the sediment eat. With a slightly lower voltage, the electrode becomes eager to accept electrons; in this case, the bacteria breathe electrons onto the electrode, which generates a current. "Basically," Nealson says, "the idea is to take sediment, stick electrodes inside and then ask 'OK, who likes this?'"

In unpublished work, the USC scientists have identified up to eight different kinds of bacteria that consume electricity, and they’re all very different from each other. 

A handful of other researchers are also working on electric bacteria. Daniel Bond’s team from the University of Minnesota in St. Paul is growing bacteria that harvest electrons from iron electrodes. Lars Peter Nielsen and his colleagues at Aarhus University in Denmark have found that tens of thousands of electric bacteria can join together to form “daisy chains” that carry electrons over several centimeters (huge distances for a bacterium). Here’s a video of electric bacteria forming their “microbial nanowires.”

 

 

 

Researchers hope to use these bacteria to probe fundamental questions about life, such as the bare minimum of energy needed to sustain life. Electric bacteria have practical uses too, such as cleaning up contaminated groundwater while powering themselves using their surroundings. 

[Via New Scientist]

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