A feast of volcanic rock might not sound appealing, but some bacteria are happy to chow down on a smorgasbord of stones. And humans have put those microbial diners to work. The mining industry, for example, uses bacteria to extract copper and gold from ore.
This process, called biomining, could be especially useful when it comes to isolating rare earth elements, like yttrium and gadolinium, that are vital to modern lasers and electronic devices, Kenneth Chang reports for the New York Times. The large quantities of toxic chemicals used to mine rare earth elements on Earth become even more problematic when planning a long-term mission to space because weight reduction is a high priority. That’s why scientists worked with the International Space Station (ISS) to find bacteria that can extract rare earth elements from rock while in low gravity.
The three-week experiment was the first mining experiment in space, University of Edinburgh astrobiologist Charles Cockell tells Jonathan Amos at BBC News. While the bacteria in this study didn’t extract a lot of metal from their rock sample, the study published on November 10 in the journal Nature Communications showed that space biomining is possible.
One bacteria species, Sphingomonas desiccabilis, performed well in all gravity environments.
“We were surprised that there was no significant effect of the different gravities on the biomining, given that microgravity is known to influence the behavior of fluids,” Cockell tells Space.com’s Mike Wall in an email. “However, we think that could be because the microbes had long enough to interact with the rocks.”
Astronaut Luca Parmitano ran the experiment on the ISS, which required managing 36 matchbox-sized samples that each held a slice of basalt. Half of the samples also held a liquid with one of three species of bacteria swimming inside.
Parmitano put the samples in centrifuges, which spun the samples at just the right speed so that the bacteria inside felt the gravity of Mars, which is about 40 percent of gravity on Earth. Another set of samples didn’t spin, so those bacteria worked on their basalt slices in the ISS’s microgravity. Yet another control group of bacteria set to work on basalt on Earth.
“The idea is the biology is essentially catalyzing a reaction that would occur very slowly without the biology,” Cockell tells the New York Times.
Two of the bacteria species struggled to extract metals from their basalt samples. But one species, Sphingomonas desiccabilis, was unfazed by its low-gravity dining experience. S. desiccabilis performed twice as well as non-biological extraction processes used for comparison in the experiment. That was surprising because without gravity, there’s no external force to shift waste and resources around the bacteria, which could have stressed the bacteria out so much that they wouldn’t mine for metals. Instead, S. desiccabilis didn’t seem to mind.
But the bacteria extracted only a very small amount of rare earth elements from the basalt samples, Payam Rasoulnia, who studies biomining of rare earth elements at Tampere University, tells the New York Times. For example, S. desiccabilis extracted an average of five billionths of a gram of lanthanum from the squares of basalt, which measured just over half an inch on each side.
The experiment wasn’t meant to simulate commercial biomining; it was testing whether it was possible in low-gravity environments.
To scale up the system, "you would probably want to modify it — for example, by stirring the fluid and crushing the rock to improve its accessibility to the microbes, but the basic idea would be the same," says Cockell to Space.com. Next, the team plans to conduct a similar experiment using asteroid material in place of the basalt.
The results are encouraging for research focused on using resources available in space destinations. Other ongoing studies are observing how astronauts on the moon may be able to use buried ice for drinking water. Likewise, the Perseverance Mars rover is carrying an experiment called MOXIE that will test whether it’s possible to make oxygen from the chemicals in Mars’ atmosphere.
One tricky requirement of bacteria, however, is that the future astronauts would still need to find a way to feed their microscopic miners, Cornell University synthetic biologist Buz Barstow tells Chemical & Engineering News’ Alla Katsnelson.
“Wherever you are in space, whether you're building a settlement on asteroids, the Moon or Mars - you're going to need elements to build your civilisation," says Cockell to BBC News. "What our BioRock experiment has shown is that biomining is just one way in which we might go about extracting useful elements from rocks to support a long-term human presence beyond the Earth."