Rowe has already had some success.
In 2013, she went on a microbe prospecting trip to the iron-rich sediments that surround California’s Catalina Island. She identified at least 30 new varieties of electric microbes in a study published last year. “They are from very diverse groups of microbes that are quite common in marine systems,” Rowe said. Before her experiment, no one knew these microbes could take up electrons from an inorganic substrate, she said. “That’s something we weren’t expecting.”
Just as fishermen use different lures to attract different fish, Rowe set the electrodes to different voltages to draw out a rich diversity of microbes. She knew when she had a catch because the current changed—metal eaters generate a negative current, as the microbes suck electrons from the negative electrode.
Yamini Jangir, then a graduate student in Moh El-Naggar’s lab at the University of Southern California, collects water from a pipe at the Sanford Underground Research Facility nearly a mile underground.
The different varieties of bacteria that Rowe collected thrive under different electrical conditions, suggesting they employ different strategies for eating electrons. “Each bacteria had a different energy level where electron uptake would happen,” Rowe said. “We think that is indicative of different pathways.”
Rowe is now searching new environments for additional microbes, focusing on fluids from a deep spring with low acidity. She’s also helping with El-Naggar’s gold mine expedition. “We are trying to understand how life works under these conditions,” said El-Naggar. “We now know that life goes far deeper than we thought, and there’s a lot more than we thought, but we don’t have a good idea for how they are surviving.”
El-Naggar emphasizes that the field is still in its infancy, likening the current state to the early days of neuroscience, when researchers poked at frogs with electrodes to make their muscles twitch. “It took a long time for the basic mechanistic stuff to come out,” he said. “It’s only been 30 years since we discovered that microbes can interact with solid surfaces.”
Given the bounty from these early experiments, it seems that scientists have only scratched the surface of the microbial diversity that thrives beneath the planet’s shallow exterior. The results could give clues to the origins of life on Earth and beyond. One theory for the emergence of life suggests it originated on mineral surfaces, which could have concentrated biological molecules and catalyzed reactions. New research could fill in one of the theory’s gaps—a mechanism for transporting electrons from mineral surfaces into cells.
Moreover, subsurface metal eaters may provide a blueprint for life on other worlds, where alien microbes might be hidden beneath the planet’s shallow exterior. “For me, one of the most exciting possibilities is finding life-forms that might survive in extreme environments like Mars,” said El-Naggar, whose gold mine experiment is funded by NASA’s Astrobiology Institute. Mars, for example, is iron-rich and has water flowing beneath its surface. “If you have a system that can pick up electrons from iron and have some water, then you have all the ingredients for a conceivable metabolism,” said El-Naggar. Perhaps a former mine a mile underneath South Dakota won’t be the most surprising place that researchers find electron-eating life.
This post appears courtesy of Quanta Magazine.