Rock-munching microbes have a weighty job in the mining industry, extracting metals such as copper and gold from the earth. They could also extract rare-earth elements such as lanthanides, scandium, and yttrium—pricey minerals used in electronics and some metal alloys.
Such microbes could also help mining in space, according to a new study (Sci. Adv. 2020, DOI: 10.1038/s41467-020-19276-w). Experiments conducted on the International Space Station (ISS) showed that the bacterium Sphingomonas desiccabilis was as efficient at extracting 14 different rare-earth elements from basalt under microgravity conditions similar to those on the moon and on Mars, as it is under Earth-like gravity.
That means a human settlement on the moon or on Mars could potentially extract rare-earth elements from the local surroundings to use in building rovers, electronic equipment, and other technology, says Charles Cockell, an astrobiologist at the University of Edinburgh, who led the study. “Wherever we go, we are going to have to mine planetary or asteroid materials to sustain a long-term presence in space,” he says. “Here is a demonstration of one particular approach.”
On the ISS, astronauts added the bacterium and basalt in miniature reactors under microgravity conditions and in specially designed incubators that contain centrifuges capable of simulating gravity on Mars and Earth. The team picked basalt because it has a high concentration of rare-earth metals and is similar to rock found on the moon and Mars. Fluids don’t mix as well in microgravity as they do on Earth, so Cockell and his colleagues speculated that the microbes might not munch the basalt as effectively. But after 3 weeks, the bugs turned out to perform similarly well under all three gravity conditions. “It was really the first mining experiment in space,” Cockell says.
Some microbes extract metal from rock by acidifying the medium, but that wasn’t the case here. Instead, S. desiccabilis excretes polysaccharides that bind to metals, preferentially grabbing rare-earth metals. Cockell and his colleagues are now working out how exactly the microbes leech out the metals.
The great thing about the approach is that a tiny vial of cells can self-assemble into a mining operation, says Buz Barstow, a synthetic biologist at Cornell University, who was not involved in the study. But rare-earth elements are relatively rare, he says, so a lot of microbes would be needed to generate even small amounts of the minerals, and those cells would need a lot of sugars to power their metabolism. Scientists will have to figure out how to produce enough nutrients in space to support the cells’ growth, he says.
“There are obviously many steps” from this prototype to a biomining system that could be used in space, Barstow says, “but they’ve got a great start.”