When nuclear fuel is produced, toxic uranium contamination of the environment can occur at any stage. Fortunately, a bacterial process can safely prevent the mobility of uranium contamination and the risk of exposure. Geobacter bacteria are tiny microorganisms that have the potential to significantly aid in the cleanup of polluted sites worldwide, according to Reguera, an MSU AgBioResearch scientist.
It is well-established that Geobacter can immobilize uranium. However, the discovery that the new discovery at hand is that the conductive pili of Geobacter’s are a major component of this mechanism. The scientists found that the electrical activity during a toxic cleanup was due to the conductive pili (nanowires).
“Th[e nanowires] are essentially performing nature’s version of electroplating with uranium, effectively immobilizing the radioactive material and preventing it from leaching into groundwater,” Reguera explained. Not only do the nanowires do this incredible work, they are also responsible for the Geobacter to survive and thrive and polluted, inhabitable environments.
Researchers demonstrated Geobacter’s efficacy in a Colorado uranium mill tailings site by injecting acetate into contaminated groundwater. This injection stimulated Geobacter, as acetate is the bacteria’s ideal sustenance. Eventually, the Geobacter population grew and also removed the uranium at the site.
During this study, the researchers found that nearly three-quarters of the cleanup capacity was catalyzed by the Geobacter’s nanowires. Now, the researchers were not only interested in the bacteria itself, but the mechanisms happening at this remarkable organism’s cell surface that cleaned uranium without the pili.
With funding from the U.S. National Science Foundation, the team found those answers, including the insight that lipopolysaccharides coat Geobacter’s cell surface, allowing it to absorb uranium efficiently. “This discovery is significant because it clarifies the detoxification and mineralization strategy used by Geobacter sulfurreducens, which may apply to other metals,” said program director of NSF’s Division of Earth Sciences, Enriqueta Barrera.
The results from the study, now published in the journal Applied and Environmental Microbiology, can provide innovative solutions for remediating toxic, dangerous pollution. Further, these insights indicate that these bacteria have the potential to reclaim and recycle rare metals from electronic waste. Reguera also said that other potential applications worth investigating include whether Geobacter can extract toxic metals from other sources of waste.
Reguera and her colleagues were able to genetic engineer a Geobacter strain to produce more nanowires. The modified version increased the bacteria’s efficiency at immobilizing uranium proportional to the nanowires on the cell surface.
This incredible research was funded by the U.S. Department of Energy and The National Institute of Environmental Health Science. Important members of the research team included Dena Cologgi, Allison, Speers, SanelaLampa-Pastirk, Shelly Kelly, and MSU graduate students.
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Cologgi, D. L., Lampa-Pastirk, S., Speers, A. M., Kelly, S. D., &Reguera, G. (2011). Extracellular reduction of uranium via Geobacter conductive pili as a protective cellular mechanism. Proceedings of the National Academy of Sciences, 108(37), 15248–15252. https://doi.org/10.1073/pnas.1108616108
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