Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Uranium 'pearls' before slime

09.08.2006
PNNL-led team discovers that bacteria roll out carpet of goo that converts deadly heavy metal into less threatening nano-spheres

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.

The pearl is uranium dioxide, or uraninite, which moves much less freely in soil than its soluble counterpart, a groundwater-contamination threat at nuclear waste sites.

The U.S. Department of Energy estimates that uranium contaminates more than 2,500 billion liters of groundwater nationwide; over the past decade, the agency has support research into the ability of naturally-occurring microbes that can halt the uranium's underground migration to prevent it from reaching streams used by plants, animals and people.

Assembling a battery of evidence, scientists have for the first time placed the bacterial enzymes responsible for converting uranium to uraninite at the scene of the slime, or "extracellular polymeric substance" (EPS), according to a study led by the DOE's Pacific Northwest National Laboratory in today's advance online edition of PLoS Biology.

"Shewanella really puts a lot of stuff outside the cell," said PNNL chief scientist Jim Fredrickson, the study's senior author. "It's very tactile compared with pathogens, which go into hiding to evade detection by the immune system."

Another oddity is Shewanella's ability to "breathe," or reduce, metals the way we human beings do oxygen. When oxygen is unavailable, Shewanella can pass excess energy during respiration in the form of electrons to metal and alter the metal's chemistry in the bargain--for instance, turning soluble uranium into solid, insoluble uraninite (uranium dioxide).

Fredrickson, PNNL staff scientist/lead author Matthew Marshall and colleagues wondered whether uranium-reducing components in that stuff outside the cell, the EPS, might help Shewanella seek out and lock up heavy metals.

To pose that question, which remains open, they first had to prove that the same metal-reducing enzymes--proteins called c-type cytochromes--associated with uraninite formation in the outer membrane could also be found outside the cell in the EPS.

This they did through a variety of experiments that included creating mutant strains unable to make outer-membrane cytochrome, or OMC, leading to an excess of uraninite particles forming only inside the cell, in the periplasm – the region between the microbe's cell and outer membrane. In nonmutants, on the other hand, OMC and uraninite were found mainly outside the cell in association with the EPS.

Collaborators from Argonne National Laboratory applied X-ray fluorescence microscopy at the Advanced Photon Source to show that iron, which is also found in OMC, was in the uraninite-EPS complex. Combining high-resolution microscopy and OMC-specific antibodies, the researchers repeatedly found the metal-reducing proteins in the uraninite-EPS complexes.

The authors noted that the OMC-containing EPS may be involved in the transfer of electrons outside the cell or is possibly a way the microbes shed the uraninite particles.

"Regardless," Fredrickson said, "the sticky EPS may behave like glue and bind the uranium particles to soil, further impeding its migration in the environment."

Bill Cannon | EurekAlert!
Further information:
http://www.pnl.gov

More articles from Life Sciences:

nachricht New risk factors for anxiety disorders
24.02.2017 | Julius-Maximilians-Universität Würzburg

nachricht Stingless bees have their nests protected by soldiers
24.02.2017 | Johannes Gutenberg-Universität Mainz

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Stingless bees have their nests protected by soldiers

24.02.2017 | Life Sciences

New risk factors for anxiety disorders

24.02.2017 | Life Sciences

MWC 2017: 5G Capital Berlin

24.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>