Bacterial Nanowires Shown to Immobilize Uranium Contaminants

Gemma Reguera and her team

Gemma Reguera (right) and her team of scientists who conducted the research on the Geobacter nanowires: (left to right) Allison Spears, microbiology doctoral student, Sanela Lampa-Pastirk, post-doctoral researcher, and Dena Cologgi, microbiology doctoral student. Photo by Michael Steger.

Stopping the spread of radioactive Uranium and other harmful pollutants can be achieved with the use of protein nanowires produced on the outside of a group of bacteria called Geobacter, scientists at Michigan State University have determined.

The nanowires, or pili, are hair-like protein appendages with electrical conductivity and can, by themselves, catalyze the process of bioremediation.

“Understanding exactly how Geobacter bacteria and their nanowires are able to immobilize harmful materials greatly advances our ability to stop pollutants like uranium and other toxic metals from spreading,” says Gemma Reguera, assistant professor of microbiology. “Scientists have searched for how these microorganisms do this for nearly twenty years. Our research clearly identifies the conductive pili on the outside of the cells as the primary catalyst of this electron transfer reaction.”

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The nanowires are essentially performing nature’s version of electroplating with uranium. The Geobacter pili conduct electrons outside and away from the cell. The pili convert radioactive Uranium (VI) to Uranium (IV) which is no longer soluble and can be contained.

During the process, the nanowires also shield the Geobacter cells from the toxic uranium and allow the bacteria to thrive and continue to immobilize the uranium in contaminated environments.

Geobacter are a group of bacteria ubiquitous in soil. The use of Geobacter in bioremediation of pollutants has continued to gain popularity, yet scientists had not understood how the organism catalyzes these reactions while thriving in inhospitable environments.

Using a genetic approach as well as sensitive spectroscopy analysis, Reguera and her team of researchers identified the conductive pili as the elusive uranium reductase in the model organism Geobacter sulfurreducens.

Making Bioremediation More Efficient

The researchers also developed a modified strain with improved pili production. These improvements enhanced the efficiency of the bioremediation process and show promise for the development of better-performing Geobacter strains that can be used in bioremediation and advanced energy technologies.

“This tiny microorganism can play a major role in cleaning up polluted sites around the world,” Reguera says. “Uranium contamination can occur at any step in the cycle of production of nuclear fuel – from mining, processing and enrichment to accidental spills from the nuclear plant. Contamination can spread fast and stay in the environment for many, many years. However, you can stimulate the natural Geobacter community of the soil and groundwater, or feed the improved strains in the environment. The bacteria will oxidize and precipitate the uranium.”

Reguera notes that this bioremediation process safely limits the mobility of uranium and prevents it from spreading.

The research was lead by Reguera and performed by College of Natural Science graduate students Dena Cologgi and Allison Speers along with post-doctoral researcher Sanela Lampa-Pastirk. The team also included Reguera’s collaborator Shelly Kelly, a former physicist from Argonne National Laboratory.

The findings are reported in the new issue of the Proceedings of the National Academy of Sciences, one of the nation’s most prestigious science journals. The research was funded by the National Institute of Environmental Health Science and the U.S. Department of Energy. Initial funding of the early stages of this research was provided by a Strategic Partnership Grant from the MSU Foundation. Reguera also receives support for her continuing research from MSU AgBioResearch.

 

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