Microbes mine metals, make soil on ISS

Drifting some 250 miles above the Earth, researchers aboard the International Space Station have enlisted the help from some of the smallest miners in the universe, microbes. These off-world experiments tested the possibility of using these tiny organisms to convert unsuitable space rock and regolith into soil for growing plants and food, as well as extracting valuable minerals and metals from extraterrestrial materials.

Published in Nature Communications, the findings by a study on the ISS suggest a new way we could one day use microbes to mine for valuable metals and minerals off Earth.

To combat the high cost of transporting of payloads into space – upwards of US$1,500 per kilogram (2.2 pounds) – NASA has pursued creative and unique ways to conduct its research by minimizing experimentation to "what is available in space?"

For over a decade, the team has been developing a small, matchbox-sized device called a biomining reactor that can easily be transported to and installed on the ISS. In July 2019, they finally managed to ship 18 of these biomining reactors to the space station for low-orbit experiments.

Before testing the possibilities of transforming celestial dirt into suitable growing soil in planetary settlements, they first needed to test it in space.

This study, called BioRock, involved a series of 36 experiments that took place aboard the ISS with an international team of scientists that used the shipped biomining reactors to determine the use of single-celled organisms, which can often survive in harsh conditions and even within the vacuum of space, in a process called biomining.

This process is actually used to extract roughly 20% of the world's copper and gold for human use and has been a popular method of metals extraction on Earth for many years, so the scientists wanted to know if it worked in microgravity as well.

For these experiments, each reactor contained a bacterial solution containing a small slice of basalt rock, which is a volcanic rock abundant on the moon and Mars. Then for three weeks, the basalt rock in each reactor was exposed to a bacterial solution and examined to determine whether the bacteria could extract minerals from the rock in a way similar to how it does on Earth.

On the space station, these bioreactors were placed inside a centrifuge to simulate three different gravitational environments – microgravity, simulated Martian gravity and simulated Earth gravity – with three different kinds of bacteria – Sphingomonas desiccabilis, Bacillus subtilis and Cupriavidus metallidurans – as well as a control solution with no bacteria at all.

The study determined that B. subtilis and C. metallidurans yielded similar results to the control solution, while the S. desiccabilis managed to extract significantly more REE from the basalt than the solution.

It was also noted that S. desiccabilis was capable of extracting rare earth elements like neodymium, cerium and lanthanum about as effectively in lower-gravity environments as they do on Earth.

The researchers aboard the ISS have been able to show that bacteria can increase mining efficiency by more than 400% and these findings pave the way for easier access to materials such as magnesium, iron and other rare earths.

More specifically, the bacterium managed to leach between 111.9% and 429.2% more of the REE than the control solution.

The team also noted that the different gravitational forces did not seem to affect the performance of any of the bacteria, which came as a surprise given that previous studies found that microgravity affects microbial processes.

It was also found that each bacterium reached similar concentrations in all three gravitational conditions, which is attributed to having sufficient nutrients to grow.

Concluded by the research team, with sufficient nutrients, biomining can significantly enhance REE extraction in several gravitational conditions that may occur in space.

At present, microbes will not replace standard mining technologies if mining is to ever happen in space, however, it could definitely help speed things up.

The team behind BioRock suggests that while microbes could help accelerate mining on extraterrestrial bodies by as much as 400% by helping to separate metal powders and valuable minerals from other useful elements like oxygen.

It is the fact that they seem able to withstand microgravity that suggests microbes could be a potentially cheap way to extract resources to make life in space more sustainable.

While it is still not necessarily economically viable to return materials harnessed from this process to Earth, the researchers say that biomining may nevertheless play a key role in supporting a self-sustaining human presence in deep space to possibly enable lengthy journeys and settlements on distant worlds.