An international research collaboration conducted an experiment on the International Space Station (ISS) to study the potential of microbes to extract valuable elements from asteroid-like material in microgravity. The BioAsteroid project, involving a bacterium and a fungus, found that the fungus Penicillium simplicissimum was particularly effective at enhancing the leaching of platinum group elements, such as palladium, under space conditions. The study also observed that microgravity itself influenced non-biological leaching processes.
The fungus Penicillium simplicissimum was particularly effective at enhancing the leaching of platinum group elements, such as palladium, under space conditions.
Introduction
Researchers from Cornell University and the University of Edinburgh collaborated on the BioAsteroid experiment, conducted aboard the International Space Station. The findings were published on January 30 in the journal npj Microgravity.
The primary objective was to investigate how microorganisms can extract minerals from rocks in microgravity, assessing the potential for "biomining" as a method for in-situ resource utilization (ISRU) during future space missions. Understanding microbial interactions with rocks in microgravity is considered crucial for deep space exploration and could offer sustainable resource alternatives to transporting materials from Earth.
Methodology
The 19-day experiment was performed on the ISS by NASA astronaut Michael Scott Hopkins, with a control version simultaneously conducted in a laboratory on Earth under normal gravity.
Materials
The study utilized samples of L-chondrite meteorite, a common stony meteorite type. Pre-experiment analysis of the meteorite identified dominant minerals such as olivine and enstatitic pyroxene. Magnesium, iron, sulfur, and manganese were the most abundant elements, with palladium present in trace amounts.
Microorganisms
The researchers employed the bacterium Sphingomonas desiccabilis and the fungus Penicillium simplicissimum, as well as a mixed consortium of both.
Analysis
Microscopy confirmed that both microbial species colonized the meteorite fragments under both microgravity and terrestrial conditions. The team performed a metabolomic analysis to examine biomolecules and analyzed data covering 44 different elements, of which 18 were biologically extracted.
Key Findings
Microbial Leaching
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Fungal Effectiveness: The fungus Penicillium simplicissimum enhanced the mean leaching of all three platinum group elements (ruthenium, palladium, and platinum) in microgravity compared to non-biological controls. The fungal enhancement of palladium extraction in microgravity was 5.5-fold relative to abiotic controls.
Specific extraction rates achieved by the fungus included 19.29% for ruthenium, 11.91% for palladium, and 0.29% for platinum.
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Consistency: Microbes demonstrated consistent extraction levels for certain metals irrespective of gravity conditions.
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Bacterium and Consortium: The bacterium Sphingomonas desiccabilis generally performed similarly to or worse than controls for platinum group elements in microgravity. The mixed consortium showed similar results to the fungus alone for most elements, but palladium extraction dropped to 3.74% in microgravity, which was suggested as a possible antagonistic effect from the bacterium.
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Terrestrial Differences: On Earth, both organisms (alone or together) increased ruthenium and platinum leaching, but palladium leaching was reduced in the presence of microbes.
Abiotic Leaching in Microgravity
Microgravity itself influenced abiotic (non-biological) leaching, with results varying by element.
- Palladium: Abiotic palladium extraction was 13.6 times higher on Earth (29.5%) than in microgravity (2.2%).
- Platinum: Abiotic platinum extraction increased 1.8-fold in microgravity (0.2%) compared to Earth (0.13%).
- Ruthenium: Mean abiotic ruthenium extraction was higher in microgravity (14.8%) but not statistically significant compared to Earth (6.6%).
- Other Elements: Abiotic leaching in microgravity significantly changed for 11 other elements, including a 6.8-fold increase for aluminum and a 4.3-fold increase for iron. Sodium, conversely, leached more efficiently on Earth.
- Proposed Mechanism: Researchers suggested that altered fluid dynamics in microgravity, such as reduced convection, could contribute to these variations.
Metabolic Insights
Metabolomic analysis indicated that microgravity altered microbial metabolism, particularly in fungus-containing samples. The fungus increased its production of various molecules, including carboxylic acids, which are known to bind to minerals and facilitate their release, thereby enhancing the release of elements like palladium and platinum.
Implications for Space and Earth
The research highlights the long-term potential of biomining for resource self-sufficiency in space rather than immediate financial gain. An economic analysis indicated that the quantity of palladium extracted in this experiment would be negligible for short-term profit.
Additionally, potential terrestrial applications include efficient biomining from resource-limited environments or mine waste, and contributing to sustainable biotechnologies for a circular economy.
Limitations and Future Research
The study acknowledged limitations common in space experiments, such as high variability linked to microbial growth rates, heterogeneous meteorite composition, small sample volumes, and limited replicates. Researchers noted that a precise explanation for space's impact on microbial species for this purpose might be complex due to numerous variables, indicating that results vary based on the microbial species, space conditions, and research methods.
Acknowledgements
The research received support from the United Kingdom Science and Technology Facilities Council, the Leverhulme Trust, the University of Edinburgh School of Physics and Astronomy, and Edinburgh-Rice Strategic Collaboration Awards.