November 13, 2020. By Kolemann Lutz
Large quantities of microbial biominers might one day extract valuable metals and minerals from surfaces of celestial bodies to advance human presence beyond Earth.
Harnessing microbes to do mining work is called biomining, also referred to as bioextraction or bioleaching, that takes advantage of microbes that eat rocks, or lithotrophs. As an affordable, low energy mining tradition with little by-products, Bioming was first envisioned in the 1950s and 60s when acid-loving microbe called acidophils were discovered
to thrive on iron, copper, and magnesium-rich environments and has been an established practice for over half a century.
Chilean-based Biosigma is one of the many biomining companies that use bacteria, powered by mainly O and CO2, to extract copper from rocks and to replace extreme heat and toxic chemicals. “Using bacteria can result in extracting as much as 90% of the total metal at a pit mine, instead of merely 60%”, says Ricardo Badilla, chief executive of Biosigma. Microorganisms are also used to extract gold, iron, uranium and many other metals.
In ESA’s BioRock experiment researchers conducted a biomining experiment inside of ESA’s compact Bioreactor onboard the International Space Station (ISS) to investigate the use of microorganisms to extract 14 Rare Earth Elements (REEs) from basalt rock, a dark volcanic material that also makes up the Earth's oceanic crust and the lunar maria. The dark areas on Mars are characterized by mafic rock-forming minerals olivine, pyroxene, and plagioclase feldspar, which are common basalt minerals found all over Mars.
“For the investigation, we are using basalt rock that is naturally very vesicular, or contains lots of spaces, to see how the bacteria interact within these cavities in microgravity,” mentioned by Rosa Santomartino, a postdoctoral scientist who investigated the growth of the microbes at the University of Edinburgh.
During the summer of 2019, three bacterium species — Sphingomonas desiccabilis, Bacillus subtilis, and Cupriavidus metallidurans — were launched and tested on the ISS in 21 days of culturing at 20.16 °C in near-neutral pH levels, which is an important factor in the efficacy of biomining.
Inside the culture chamber, the microbes experienced thermal convection and sedimentation at three varying gravities — 1 G for Earth, ⅜ G to simulate Mars, and microgravity — which are thought to affect the mixing of nutrients and waste, influencing microbial growth and metabolism of metal resource extraction.
After calculating the percentage difference in bioleaching of REEs for each microorganism, researchers noticed that the presence of the gram-negative, non-motile bacterium S. desiccabilis enhanced concentrations of leached REEs in all gravity conditions. The bacterial microbes improved space mining efficiency by over 400 percent. Although there was no significant difference between organisms in Earth and simulated Mars gravity, there was a significant difference in mineral extraction efficiencies between organisms in microgravity. As indicated in figure a, S. desiccabilis caused preferential leaching of heavy metals (Gd up to Lu) over light (La up to Eu) REEs.
“The BioRock experiment starts putting the pieces of the puzzle together. BioRock is about forming a new space-faring alliance with the microbial world – using microbes to advance a permanent human presence in space" mentioned by co-lead author Charles Cockell, Professor at the UK Centre for Astrobiology at the University of Edinburgh.
S. desiccabilis could be applied on the Moon, Mars, and asteroids in pressurized, insulated environments and other biomining microbes for (i) soil formation from nutrient-poor rocks for plants and agriculture, (ii) formation of biocrusts to control dust and surface material in pressurized spaces, (iii) use of regolith as feedstock within microbial segments of life support systems, (iv) biological production of mineral construction materials, (v) use of regolith and microbes in microbial fuel cells as biofuel.
Further research is required to advance our understanding of the S. desiccabilis cell interactions with simulant perchlorates, iron and sulfur oxides, low oxygen environments, and Martian environment.
More Information. Charles S. Cockell et al, Space station biomining experiment demonstrates rare earth element extraction in microgravity and Mars gravity, Nature Communications (2020).
