very cool! June 21, 2016:

As the tally of electron eaters grows, scientists are beginning to figure out just how they work. How does a microbe consume electrons out of a piece of metal, or deposit them back into the environment when it is finished with them? A study published last year revealed the way that one of these microbes catches and consumes its electrical prey. And not-yet-published work suggests that some metal eaters transport electrons directly across their membranes — a feat once thought impossible.

The Rock Eaters
Though eating electricity seems bizarre, the flow of current is central to life. All organisms require a source of electrons to make and store energy. They must also be able to shed electrons once their job is done. In describing this bare-bones view of life, Nobel Prize-winning physiologist Albert Szent-Györgyi once said, “Life is nothing but an electron looking for a place to rest.”

Humans and many other organisms get electrons from food and expel them with our breath. The microbes that El-Naggar and others are trying to grow belong to a group called lithoautotrophs, or rock eaters, which harvest energy from inorganic substances such as iron, sulfur or manganese. Under the right conditions, they can survive solely on electricity.

The microbes’ apparent ability to ingest electrons — known as direct electron transfer — is particularly intriguing because it seems to defy the basic rules of biophysics. The fatty membranes that enclose cells act as an insulator, creating an electrically neutral zone once thought impossible for an electron to cross. “No one wanted to believe that a bacterium would take an electron from inside of the cell and move it to the outside,” said Kenneth Nealson, a geobiologist at the University of Southern California, in a lecture to the Society for Applied Microbiology in London last year.

[link to www.quantamagazine.org (secure)]