Bacterial prospectors take on the final frontier

Bacteria currently used as catalysts in earthbound mining processes could one day be used to extract critical elements in space and further the human settlement of other planets. Researchers at the University of Edinburgh struck gold with their discovery in a recent study published in the journal Nature Communications.

Led by Charles Cockell, Professor of Astrobiology at the University of Edinburgh and co-director of the UK Centre for Astrobiology, the study analysed data from the BioRock experiment performed by astronauts aboard the International Space Station (ISS) in 2019. Purpose-built biomining reactors the size of a matchbox were loaded with liquid solutions containing one of three spacefaring bacterial species – Sphingomonas desiccabilis, Bacillus subtilis and Cupriavidus metallidurans – alongside samples of basalt, a type of rock similar to that found on the Moon and Mars.

The bioreactors were kept under three differing levels of gravity – microgravity, simulated Mars gravity and Earth gravity – for three weeks. Afterwards, the concentrations of rare-earth elements leached by the bacteria were compared to control samples which hadn’t been exposed to microbial cultures. While the main experiment was conducted by European Space Agency (ESA) astronaut Luca Parmitano on the ISS 400 km above the Earth’s surface, additional control tests were run simultaneously down on solid ground.

Comparing the results from the space station to those recorded on Earth, the team found that the gravity conditions had no significant effect on the microbes’ performance. S. desiccabilis, originally isolated from soil crusts in the Colorado Plateau in the United States, was found to be especially effective, promoting the extraction of individual rare-earth elements from the basalt sample by up to 400 percent compared to the non-biological control. The other two species were deemed to have little to no effect on the leaching of the monitored elements.

Bioleaching (the use of bacteria as extraction catalysts) has been established in Earth-based mining of metals such as gold and copper over the past few decades, contributing some 20% of the world’s copper production in 2012. However, its real potential may remain untapped in the extraction of rare-earth elements. These are a group of seventeen chemical elements which, despite their name, are relatively abundant in Earth’s crust. However, they are seldom encountered in economically exploitable ore deposits, instead cropping up dispersed throughout the top layer. Due to their unique properties, rare-earth elements such as lanthanum and neodymium have found use in areas ranging from renewable energy to battery technology and consumer electronics. This makes mining them crucial in our continuing battle against the climate crisis.

Previous experiments in orbit have identified multiple species of bacteria and other extremophiles that can survive and even thrive in the hostile environment of space. Among these are cyanobacteria which are thought to have produced much of the oxygen we breathe today. The new study, however, is the first to demonstrate the viability of biomining in altered gravity conditions, potentially paving the way for industrial mining on asteroids and planetary bodies.

“While it is not economically viable to mine these elements in space and bring them to Earth, space biomining could potentially support a self-sustaining human presence in space.”

Charles Cockell

Nevertheless, earthbound battery manufacturers looking to stock up on rare-earth elements better not hold their breath. “While it is not economically viable to mine these elements in space and bring them to Earth, space biomining could potentially support a self-sustaining human presence in space,” says Professor Cockell.

Dr Rosa Santomartino, postdoctoral scientist at the University’s School of Physics and Astronomy, who worked on the project, similarly looks to the future: “Microorganisms are very versatile and as we move into space, they can be used to accomplish a diversity of processes. Elemental mining is potentially one of them.” Indeed, the researchers suggest constructing biomining facilities in Oceanus Procellarum and Mare Imbrium on the Moon, two regions known to be abundant in rare-earth elements.
In addition to extracting crucial elements, the researchers believe microbes could be used to form fertile soil from ordinarily nutrient-free rocks and produce biofuels as well as construction materials on other planets. This type of In-Situ Resource Utilisation (ISRU) could one day liberate space settlers from their dependence on Earth materials and is currently being explored by NASA as part of the Artemis mission to the Moon. Perhaps the scenes of Matt Damon planting potato crops on Mars in The Martian won’t seem quite so outlandish one day.

“Further research is still needed to ensure the best bacteria are chosen for the job.”

Further research is still needed to ensure the best bacteria are chosen for the job. “Our experiments also confirm that it is important to be careful in the selection of microorganisms for space biomining operations.” the researchers write, referring to the disappointing performance of B. subtilis and C. metallidurans in extracting rare-earth elements. When it comes to mining on the Moon, no ordinary sourdough starter will do.

Mika Kontiainen is a 2nd year Astrophysics student. Find him on Twitter @MikaKonte and LinkedIn @Mika Kontiainen.