We now have a broader understanding of a group of bacteria that use iron just like we use oxygen, and yet another type that feeds on iron, thanks to two studies conducted by researchers from a UW-Madison lab. One of them is published in Applied and Environmental Microbiology, and the other in Geobiology.
When animals feed on carbohydrates, the latter are oxidised, thereby losing electrons which are then taken up by oxygen to form water. This is why we need oxygen. Some bacteria, however, do not have access to oxygen because of their location (for example, those living underwater or underground), and, therefore, need something else to take up the electrons that result from metabolising organic matter. Some bacteria are able to use iron for this purpose; they transfer the electrons from organic matter (food) to iron oxide.
The bacteria use iron that is deficient in electrons to soak up those that are released when consuming organic matter. This iron is reduced to an electron-rich form of the element. These types of iron can also donate electrons in the complementary reactions that constitutes oxidation: there will be some other bacterial groups that will actually eat the iron to generate energy. Understanding the inner workings of these processes might help answer the mystery of the origin of life, say the researchers. Furthermore, the studies might help in the search for life on other planets, as points out senior author Eric Roden.
The metabolism of the iron-eating bacteria has been studied by Roden and his team. They collect samples thereof for analysis in their labs. For the latest scientific papers, they examined samples taken from the Chocolate Pot hot spring from the Yellowstone National Park; the spring obtained its names for the reddish-brown colour conferred onto it by ferric oxide. That was how they spotted unknown bacteria able to metabolise iron. Also, using an advanced genome-sequencing technique, they obtained genetic data that points at the ability of transferring electrons through a cell’s outer membrane in both directions: this characteristic allows the bacteria to use iron as an energy source, and also to use iron forms that could not otherwise be taken into the cell; the bacteria have previously been shown to form stalks or sheaths for the transport of iron.
Studying these bacteria might help researchers in finding ways to harvest energy from organic matter by making use of these organisms. Furthermore, the bacteria play an important life in the process of rock weathering. Also, given that some of these iron-bacteria feature at early stages on the tree of life, the findings can be made pertinent to the origin of life itself — not only on Earth, but in space as well. Roden says that bacteria on Mars might be metabolising iron instead of oxygen to survive, and the bacteria they discovered might be a model for life forms that might be out there waiting to be found.