Microbiologists have learned that certain strains of bacteria are capable of using energy in its purest form by eating and breathing electrons. It's a discovery that demonstrates an entirely new mode of life on Earth — and possibly beyond.
Called "electric bacteria," these microbes harvest electrons from rocks and metals. These microbes produce hair-like filaments that act as wires, ferrying electrons back and forth between the cells and their environment.
Scientists have already shown that two types of bacteria, Shewanella and Geobacter, are capable of doing this, but they're learning that many more strains exist, including those that can be enticed out of rocks and marine mud using electricity. New Scientist explains:
That should not come as a complete surprise, says Kenneth Nealson at the University of Southern California, Los Angeles. We know that life, when you boil it right down, is a flow of electrons: "You eat sugars that have excess electrons, and you breathe in oxygen that willingly takes them." Our cells break down the sugars, and the electrons flow through them in a complex set of chemical reactions until they are passed on to electron-hungry oxygen.
In the process, cells make ATP, a molecule that acts as an energy storage unit for almost all living things. Moving electrons around is a key part of making ATP. "Life's very clever," says Nealson. "It figures out how to suck electrons out of everything we eat and keep them under control." In most living things, the body packages the electrons up into molecules that can safely carry them through the cells until they are dumped on to oxygen.
"That's the way we make all our energy and it's the same for every organism on this planet," says Nealson. "Electrons must flow in order for energy to be gained. 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."
The discovery of electric bacteria shows that some very basic forms of life can do away with sugary middlemen and handle the energy in its purest form – electrons, harvested from the surface of minerals. "It is truly foreign, you know," says Nealson. "In a sense, alien."
Nealson's team is now growing its very own electric bacteria, keeping them alive with electricity and literally nothing else. His colleague, Annette Rowe, has identified up to eight different kinds of bacteria that eat electricity — a discovery that, as Nealson puts it, "means... there's a whole part of the microbial world that we don't know about."
Indeed, NASA is interested in microorganisms that live deep underground because these lifeforms often survive on very little energy. This suggests the potential for an entirely new mode of life in other parts of the solar system and galaxy.
What's more, these lifeforms could also be used here on earth to create biomachines capable of cleaning up sewage and contaminated groundwater, or drawing power from their surroundings.