From SLAC: “Unexpected Allies Help Bacteria Clean Uranium From Groundwater”

March 7, 2013
Lori Ann White

Since 2009, SLAC scientist John Bargar has led a team using synchrotron-based X-ray techniques to study bacteria that help clean uranium from groundwater in a process called bioremediation. Their initial goal was to discover how the bacteria do it and determine the best way to help, but during the course of their research the team made an even more important discovery: Nature thinks bigger than that.

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From left to right: Sam Webb, John Bargar and Juan Lezama-Pacheco used X-rays from the Stanford Synchrotron Radiation Lightsource to discover Nature’s housecleaning secrets. Since the housecleaning involves uranium, their curiosity may have important benefits. (Credit: Matt Beardsley)

The researchers discovered that bacteria don’t necessarily go straight for the uranium, as was often thought to be the case. The bacteria make their own, even tinier allies – nanoparticles of a common mineral called iron sulfide. Then, working together, the bacteria and the iron sulfide grab molecules of a highly soluble form of uranium known as U(VI), or hexavalent uranium, and transform them into U(IV), a less-soluble form that’s much less likely to spread through the water table. According to Barger, this newly discovered partnership may be the basis of a global geochemical process that forms deposits of uranium ore.

And it’s all done using one of the most basic types of chemical reactions known: oxidation and reduction, commonly known as ‘redox.’ Redox reactions can be thought of as the transfer of electrons from donor atoms to atoms that are hungry for electrons, and they are a primary source of chemical energy for both living and non-living processes. Photosynthesis involves redox reactions, as does cell respiration. Iron oxidizes to form rust; batteries depend on redox reactions to store and release energy.

‘Redox transitions are a very fundamental process,’ Bargar said. ‘It’s the stuff of life. It’s how you breathe.'”

The study, published Monday in the Proceeding of the National Academy of Sciences, was conducted at the Old Rifle site on the Colorado River, a former uranium ore processing site in the town of Rifle, Colo. The aquifer at the site is contaminated with uranium and is the focus of bioremediation field studies conducted by a larger team of scientists at Lawrence Berkeley National Laboratory and funded by the Department of Energy’s Office of Biological and Environmental Research. As part of their study, the LBNL team added acetate – essentially vinegar – to the aquifer in a series of injection wells to “feed the bugs,” as Bargar put it, allowing acetate to flow throughout the aquifer around the wells.

See the full article here.

SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

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