Excerpted and edited from Meet the Electric Life Forms that Live on Pure Energy by Catherine Brahic
We already knew about two types, Shewanella and Geobacter. Now, biologists are showing that they can entice many more out of rocks and marine mud by tempting them with a bit of electrical juice. Experiments growing bacteria on battery electrodes demonstrate that these novel, mind-boggling forms of life are essentially eating and excreting electricity.
That should not come as a complete surprise. 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.
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. In a sense, alien.”
A handful of scientific teams is now growing these bacteria directly on electrodes, keeping them alive with electricity and nothing else – neither sugars nor any other kind of nutrient. The highly dangerous equivalent in humans would be for us to power up by shoving our fingers in a DC electrical socket.
To grow these bacteria, the team collects sediment from the seabed, brings it back to the lab, and inserts electrodes into it. First they measure the natural voltage across the sediment, before applying a slightly different one. A slightly higher voltage offers an excess of electrons; a slightly lower voltage means the electrode will readily accept electrons from anything willing to pass them off. Bugs in the sediments can either “eat” electrons from the higher voltage, or “breathe” electrons on to the lower-voltage electrode, generating a current. That current is picked up by the researchers as a signal of the type of life they have captured. “Basically, the idea is to take sediment, stick electrodes inside and then ask ‘OK, who likes this?’”.
PhD student Annette Rowe has identified up to eight different kinds of bacteria that consume electricity “This is huge. What it means is that there’s a whole part of the microbial world that we don’t know about.”Electric bacteria could have practical uses here on Earth, however, such as creating biomachines that do useful things like clean up sewage or contaminated groundwater while drawing their own power from their surroundings. One researcher calls them self-powered useful devices, or SPUDs. NASA is also interested in things that live deep underground because such organisms often survive on very little energy and they may suggest modes of life in other parts of the solar system.
How much juice do you need to keep a living electric bacterium going? Answer that question, and you’ve answered one of the most fundamental existential questions there is. Electric bacteria come in all shapes and sizes. A few years ago, biologists discovered that some produce hair-like filaments that act as wires, ferrying electrons back and forth between the cells and their wider environment. They dubbed them microbial nanowires. Tens of thousands of electric bacteria can join together to form daisy chains that carry electrons over several centimetres – a huge distance for a bacterium only 3 or 4 micrometres long. It means that bacteria living in, say, seabed mud where no oxygen penetrates, can access oxygen dissolved in the seawater simply by holding hands with their friends.
Who says one can’t live by Prana alone….