Certain bacteria can breathe iron like we breathe oxygen. Understanding how they do so will help researchers use the microbes for cleaning up soil contaminants, trapping carbon dioxide, or making batteries out of bacteria. Now, a team of researchers report in the Proceedings of the National Academy of Sciences that proteins on the surface of bacteria produce an electric current by simply touching a mineral surface, allowing them to breathe the iron in the rock.
To do so, the team created a simulated bacterium using just the proteins thought to shuttle the electrons from the inside of the microbe to the rock. They inserted these proteins into lipid layers of vesicles, which are small bubbles of lipids such as the ones that make up a bacterial membrane. Using instruments and expertise at EMSL, the Department of Energy's Environmental Molecular Sciences Laboratory, the team showed that the proteins protruded through the lipid bubbles in the same way they do in real bacteria, known as Shewanella oneidensis.
Then they tested how well electrons traveled between an electron donor on the inside and an iron-bearing mineral on the outside. The electron transfer rate they measured was fast enough to support bacterial respiration, showing that those proteins were the only ones the bacteria would need to conduct electricity.
In addition to contaminant cleanup and biobatteries, the finding is important for understanding how carbon works its way through the atmosphere, land and oceans. If researchers understand electron transfer, they can learn how bacteria control the carbon cycle.