Cleaning uranium waste with bacteria

In the U.S. alone, the Department of Energy estimates that more than 2,500 billion liters of groundwater are contaminated with uranium. But now, scientists from the Pacific Northwest National Laboratory (PNNL) say they discovered that some common bacteria could "convert deadly heavy metal into less threatening nano-spheres."

Nuclear bombs can kill people even if they're not used. In the U.S. alone, the Department of Energy estimates that more than 2,500 billion liters of groundwater are contaminated with uranium as a consequence of nuclear weapons production. In "Uranium 'pearls' before slime," scientists from the Pacific Northwest National Laboratory (PNNL) say they discovered that some common bacteria could "convert deadly heavy metal into less threatening nano-spheres." In fact, these bacteria can convert soluble radioactive uranium into a non-toxic solid form called uraninite. Still, more research needs to be done before using these bacteria on a large scale, but it's a step in the good direction. Read more...

Here is the introduction of the PNNL news release.

Since the discovery a little more than a decade ago of bacteria that chemically modify and neutralize toxic metals without apparent harm to themselves, scientists have wondered how on earth these microbes do it.
For Shewanella oneidensis, a microbe that modifies uranium chemistry, the pieces are coming together, and they resemble pearls that measure precisely 5 nanometers across enmeshed in a carpet of slime secreted by the bacteria.

Below is a picture of Shewanella oneidensis, this microbe which can help us to decontaminate groundwater at nuclear waste sites (Credit: PNNL). According to this page at PNL, "S. oneidensis is a versatile bacterium that can use a variety of organic compounds and metals as electron acceptors for respiration. Many of the compounds and metals that "S. oneidensis can use as electron acceptors, such as uranium, chromate, technetium, and nitrates, can be toxic to humans and other organisms and are contaminants of concern at a number of DOE sites."

Shewanella oneidensis

And below is a picture showing how "soluble uranium has been converted to solid uraninite (UO2), strung like tiny pearls along branching extracellular polymeric substance, a slime secreted by Shewanella bacteria" (Credit: PNnL). The researchers prefer to speak about "Heme staining of extracellular cytochromes from S. oneidensis MR-1."

Soluble uranium converted to solid uraninite

[Note: according to this page on Wikipedia, "a heme is a metal-containing cofactor that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Although porphyrins do not necessarily contain iron, a substantial fraction of porphyrin-containing metalloproteins do in fact have heme as their prosthetic subunit."]

This research work, led by PNNL chief scientist Jim Fredrickson, has been published in an advance online edition of PLoS Biology under the title "c-Type Cytochrome-Dependent Formation of U(IV) Nanoparticles by Shewanella oneidensis" (Volume 4, Issue 8, August 2006). Here is a link to a summary of this paper, called "Cultivating Bacteria's Taste for Toxic Waste," and written in plain English.

But if you want more technical information, here are two links to the full version of this scientific paper, as a text version or in PDF format (10 pages, 2.4 MB). The above figures have been extracted from this paper.

Sources: Pacific Northwest National Laboratory news release, August 7, 2006; and various web sites

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