Metal-powered microbes pump electrons straight out of minerals
The energy powering most organisms on Earth can be traced back to the Sun. Sunlight helps plants grow, animals eat those plants, etc. Even creatures that live their whole life in complete darkness can benefit from this cycle, as long as something else is willing to poop or die in their vicinity. Solar dependency isn’t the only way to live though, and scientists are just digging into the swath of microbes that power their biological processes through other means, such as feeding at toasty-hot geothermal vents, or even cold hunks of metal, buried a mile under the ground.
Making a living off of minerals
One set of such lithoautotrophic, or rock-eating, microbes was found in water near a gold mine, at least a mile underground. With no access to light, organic waste from other creatures, or even much oxygen, the microbes were found to make due by grabbing electrons, basically drawing electricity, out of the mineral deposits they lived on. While there was speculation that the microbes were somehow passing electrons straight through their outer membranes, it was found that species like Methanococcus maripaludis utilized an enzyme to set up such a transfer. The enzyme would grab an electron from the metal, and a proton from water, then pair them as a hydrogen atom that could be ingested by the microbe. Other species used antennae-like “nanowires” to collect electrons so that they could be used for metabolic activity.
This unusual arrangement allows for the nearby metal to be a substitute for sunlight. The microbes still need access to organic compounds to build their cell membranes, assemble enzymes, etc., but the energy source to run things is the electrons siphoned off the iron or other metal the microbes call home. They’re not “eating” the metal in the way you eat an apple, breaking it down for energy and organic material, but the loss of electrons does eventually start to break the metal down, meaning these microbes can’t just cycle their electrons through the surrounding minerals for all the energy they’d want.
Location, location, location
The ecology of these microbes raises some interesting possibilities for life on other planets. While none of their chemistry is really at odds with most of the organisms we know about, not needing access to staples like oxygen or sunlight does allow for a wide variety of habitats. One place these microbes aren’t often found though is in comfortable lab where researchers can work with them. There have been recent successes keeping some species alive on electrodes in a lab environment, but for a long time many questions about these electron-siphoning microbes have been hard to answer since they were so hard to keep alive where the rest of us like to live. As our body of knowledge grows, it might turn out these strange ecologies will turn out to be more common than expected.
Source: New Life Found That Lives Off Electricity by Emily Singer, Quanta Magazine
