Recent experiments aboard the International Space Station have shown that some microbes can harvest valuable rare-earth elements from rocks, even when exposed to microgravity conditions. The unexpected finding shows how microbes could boost our ability to live and work in space.
On Earth, some microscopic organisms have shown their worth as effective miners, extracting rare-earth elements (REEs) from rocks. New experimental evidence published today in Nature Communications shows that, when it comes to leaching REEs from rocks, at least one strain of bacteria is largely unaffected by microgravity and low-gravity conditions. This is potentially good news for future space explorers, as biomining microbes could provide a means for acquiring REEs while in space, on the Moon, or on Mars.
REEs are vitally important for the manufacturing of commercial electronic components (like those found in your smartphone) and the production of alloys. The problem with REEs, aside from their tricky names (e.g. lanthanum, cerium, neodymium, yttrium, praseodymium, just to name a few), isn’t so much that they’re rare as they’re notoriously difficult to mine and extract, making them a serious pain in the arse. In addition to the increased mining and refining costs, the harvesting of these elements is both ecologically and environmentally unfriendly, and the insatiable quest to obtain them often results in civil strife, which is why they’re often referred to as “conflict minerals.” Frustratingly, these elements, with their unique magnetic and catalytic properties, are without viable substitutes.
This is why microbes are being recruited to help, in a technique known as biomining.
“Microbes can be specific in the sorts of elements they bind, and they allow us to do away with large quantities of environmentally destructive chemicals, like cyanides, traditionally used to leach elements from rocks,” Charles Cockell, the lead author of the new study and an astrobiologist at the University of Edinburgh, explained in an email. “These days, we can even engineer them to be better miners.”
These microbes perform their magic by producing sugars, which bind to REEs. This causes the elements to concentrate together, making extraction easier.
To determine if biomining is possible off Earth, an experiment was set up in the International Space Station — a unique laboratory in which microbes can be exposed to microgravity and low-gravity conditions. That altered gravity might affect the microbes’ ability to perform their duties was a distinct possibility, as such conditions “are known to influence microbial growth and metabolic processes,” according to the study.
“Low gravity is known to reduce the settling of microbes and so reduce the mixing and flow of nutrients to microbes and waste away from them,” said Cockell. “So we could expect that this might indirectly influence the growth of the microbes and how they interact with rocks, and thus their ability to biomine those rocks.”
Three different bacteria were used in the experiment: Sphingomonas desiccabilis, Bacillus subtilis, and Cupriavidus metallidurans. These tests were commissioned by the European Space Agency as part of its BioRock experiment, which was conducted on the ISS in 2019. The aim of the project was to see if microbes could leach an assortment of REEs from basalt — a good analogue for materials found on the Moon and Mars.
The authors measured the extraction efficiency of the microbes when exposed to three different conditions: microgravity, Mars gravity, and Earth gravity. To do so, the ISS astronauts placed the microbes in a miniaturized biomining reactor known as KUBIK.
“This is an incubator that controls the temperature, but it also contains a ring that spins around — a centrifuge,” explained Cockell. “We put our biomining reactors in the ring and spun them at exactly the right speed to simulate Mars and Earth gravity — the Earth gravity being a ‘control’ experiment to make comparisons.”
Of the three bacterial species, only one, S. desiccabilis, displayed an ability to leach REEs from the basaltic rock under all conditions. This bacterium didn’t seem to be bothered by any of the three gravitational environments, displaying 70% extraction efficiency for the REEs cerium and neodymium. The other two bacteria either showed very poor performance or no ability at all when exposed to any of the experimental conditions.
As to why S. desiccabilis did so well while its microbial comrades did not, Cockell said his team thinks it’s because this bacterium produces “lots of long-chained sugars that have many binding sites on them that bound the rare-earth elements.” The other microbes didn’t do this, he said, adding: “We did wonder whether the other microbes might be stimulated into doing biomining by the stressful conditions of lack of nutrients in microgravity — which is why we sent them — but microgravity did not change their ability or allow them to biomine.”
The new research shows that specific microbes (there could be more, or, if not, scientists could produce genetically engineered versions) will probably work as REE extractors in space. Needless to say, these microbes would die if exposed to the elements, so this imagined refining process will require some clever technologies. Cockell envisions gas- and fluid-filled bioreactors near lunar habitats, on Mars, and even on asteroids. Promising rocks would be placed into the reactor along with the requisite microbes, the chamber sealed and pressurised, and, voilà — you’ve started the biomining process.
Cockell said it’s important to point out that his team isn’t proposing to do mining in space and deliver the materials back to Earth.
“At the moment, that’s not economically viable,” he said. “However, biomining and other forms of mining can be used to provide the elements needed for a long-term human presence in space. Our experiment has explored and demonstrated the potentially important role of microbes in facilitating the human expansion into space.”
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The authors will now turn their attention to an exciting experiment, called BioAsteroid, that will launch to the ISS in December. The experiment will use meteorite material as a stand-in for asteroid rock, as well as fungi with a proclivity for mining rocks. BioAsteroid will also involve exposure to microgravity conditions, to assess the viability of using fungi for the biomining of asteroids.