BIO-MINING: The cyanobacterium Anabaena cylindrica is commercially used as a natural fertilizer in rice paddies. Scientists also found it could help mine oxygen, nutrients and minerals in space. Image: Karen Olsson-Francis
Microbes currently are used in mining to help recover metals such as gold, copper and uranium. Now researchers suggest bacteria could be enlisted for "bio-mining" in space, to extract oxygen, nutrients and minerals from extraterrestrial bodies such as the moon and Mars for use by future colonists there.
More than a quarter of the world's copper supply is currently harvested from ores using microorganisms. As such, geomicrobiologists Karen Olsson-Francis and Charles Cockell at The Open University in Milton Keynes, England, reasoned that microbes could get drafted for use in space exploration as well—"it's just a question of transferring that technology to other planetary surfaces," Cockell says. "It would be a way of living off the land in space."
The researchers experimented with a variety of cyanobacteria, often known as blue-green algae, on analogues of lunar and Martian regolith (loose surface rock). These photosynthetic bacteria have adapted to live in some of the most extreme environments on Earth, from the cold, hyper-arid Antarctic McMurdo Dry Valleys to the hot, dry Atacama Desert in Chile, suggesting they might be capable of surviving the rigors of outer space.
The scientists investigated three cyanobacteria species used commercially as foodstuff or to help plants grow—for instance, Anabaena cylindrica is used as a natural fertilizer in rice paddies. They also studied species adapted to more extreme conditions—one strain was taken from Nubian sandstone in the Negev Desert, whereas three others, originally found growing on limestone cliffs in England, were launched 300 kilometers into low Earth orbit and exposed to vacuum, cold, heat and radiation. All the microbes were then grown with water on a variety of rock types, including anorthosite from South Africa (analogous to lunar highland regolith) and basalt from an Icelandic volcano (similar to lunar and Martian regolith).
The cyanobacteria could grow on all the different rock types, with A. cylindrica growing five times faster on average than the other species tested. The microbes could also extract calcium, iron, potassium, magnesium, nickel, sodium, zinc and copper from the rocks, with A. cylindrica showing the most such activity.
The scientists also found A. cylindrica and the more extreme-loving cyanobacteria could survive 28 days under extremely low temperatures and pressures simulating Martian conditions, provided they were covered with a shield against ultraviolet rays. "Although we would want to grow these bacteria in vats in pressurized habitats, there's always a possibility of a malfunction that exposes them to lunar or Martian conditions, so you want to see if they all die or not, especially if people are depending on them for their lives," Cockell says. The extreme-loving cyanobacteria and A. cylindrica could also tolerate 28 days of extreme dryness, suggesting they could be freeze-dried for easy transport and storage.
These findings suggest that A. cylindrica would be the ideal cyanobacterium to use in space among those tested so far, because it grew the fastest, extracted the most elements overall, and could withstand both super-dry and Martian conditions. A. cylindrica is also a nitrogen-fixing cyanobacterium, which means it could help generate nitrogen-rich compounds key for life, such as the amino acid–building blocks of proteins and the nucleotides making up DNA and RNA. The scientists detailed their findings in the August issue of Planetary and Space Science.
The advantages of using microbes for bio-mining are many, Cockell says. Although chemicals could be used to extract minerals from extraterrestrial regolith, "microbes catalyze this extraction at much faster rates than using pure chemicals," he explains. Using purely chemical systems would also take a lot of energy, which early extraterrestrial outposts will likely lack.
Plants could also be used to generate oxygen, but microbes grow a lot faster than plants, and they can generate far more oxygen with microbes in a vat than for the same volume of plants, with a simpler growing process, Cockell says. Also, cyanobacteria may not sound palatable, but one species the researchers tested, Arthrospira platensis, is edible and "tastes a bit like seaweed," he adds. For those who might not think of cyanobacteria as fine cuisine, microbes can still be used to break down rock and make it better for crop growth, he explains.
"We will not be able to colonize either the moon or Mars without development of cyanobacterial biotechnologies," says astrobiologist Igor Brown, who did not take part in this study. Previously, at NASA, Brown and his colleagues successfully grew cyanobacteria from hot springs in Yellowstone National Park on iron-rich rocks designed to simulate lunar material.
"There are processes one could use to dissolve lunar regolith with special chemicals, but the costs of delivering such compounds to the moon is enormous," Brown says. "That is why we propose using just vials of microbes instead. "Scientists could also genetically engineer new microbes that are even better at bio-mining, he adds.