AFM, optical microscopy show bacteria 'breathing' toxic metals

COLUMBUS, OH, USA--Using a combination of atomic force microscopy and optical microscopy, an international team led by researchers at Ohio State University have been able to witness how a common soil bacterium "inhales" toxic metals and "exhales" them in a non-toxic form. It is hoped the bacteria might one day clean up toxic chemicals left over from decades-old nuclear weapons production.

Their work is described in a study published by the journal Applied and Environmental Microbiology, which provides the first evidence that Shewanella oneidensis bacterium maneuvers proteins within the bacterial cell into its outer membrane to contact metal directly. The proteins then bond with metal oxides, which the bacteria use for energy--the same way we use oxygen.

We use the oxygen we breathe to release energy from our food. But in nature, bacteria don't always have access to oxygen, explained Brian Lower, assistant professor in the School of Environment and Natural Resources at Ohio State. "Whether the bacteria are buried in the soil or underwater, they can rely on metals to get the energy they need," Lower said. "It's an ancient form of respiration."

"This kind of respiration is fascinating from an evolutionary standpoint, but we're also interested in how we can use the bacteria to remediate nasty compounds such as uranium, technetium, and chromium." The last two are byproducts of plutonium. The United States Department of Energy is sponsoring the work in order to uncover new methods for treating waste from nuclear weapons production in the 1960s and '70s.

Shewanella is naturally present in the soil, and can in fact be found at nuclear waste sites such as the Hanford site in the state of Washington, Lower explained. With better knowledge of the bacterium's abilities, scientists might one day engineer a Shewanella that would remediate such waste more efficiently. "For instance, if you could enhance this bacterium's ability to reduce uranium by having it make more of these key proteins, that could perhaps be one way to clean up these sites that are contaminated," he said.

The danger at such waste sites is that the toxic metals are soluble, and so can leak into the local water supply. But these bacteria naturally convert the metals into an insoluble form. Though the metals would remain in place, they would be stable solids instead of unstable liquids.

For this study, Lower and his colleagues used an atomic force microscope (AFM) to test how the bacterium responded to the metallic mineral hematite. An AFM works somewhat like a miniaturize phonograph needle: a tip dangles from a cantilever above a surface that's being studied. The cantilever measures how much the tip rises and falls as it's dragged over the surface. It can measure features smaller than a nanometer, and detect atomic forces between the probe tip and the surface material.

They combined the AFM with an optical microscope to get a precise map of the bacteria's location on the hematite. Though the bacteria are very small, they are thousands of times bigger than the tip of an AFM probe. So the microscope was able to slide over the surface of individual bacteria to detect protein molecules on the cell surface and in contact with the metal.

The researchers coated their probe tip with antibodies for the protein OmcA, which they suspected Shewanella would use to "breathe" the metal. Whenever the probe slid over an OmcA protein, the antibody coating would stick to the protein. By measuring the tiny increase in force needed to pull the two apart, the researchers could tell where on the bacteria surface the proteins were located.

The microscope detected OmcA all around the edges of the bacteria, wherever the cell membrane contacted the hematite--which suggests that the protein does indeed enable the bacteria to "breathe" hematite. The protein was even present in a gelatinous ooze that was seeping from the bacteria. This suggests that Shewanella might create the ooze in order to obtain energy from a wider portion of the metal than it can directly touch, Lower said.

In the future, he and his partners want to test their new microscope technique on other types of cells. They also want to test whether Shewanella produces OmcA on the cell surface when exposed to uranium and technetium.

Lower's coauthors on the paper include researcherf from Corning, Inc.; Pacific Northwest National Laboratory; Johannes Kepler University of Linz, Austria; Ecole Polytechnique Fédérale de Lausanne, Switzerland; and Umea University, Sweden.

More information:
See the paper, Antibody-recognition force microscopy shows that outer membrane cytochromes OmcA and MtrC are expressed on the exterior surface of Shewanella oneidens, at Applied and Environmental Microbiology.

Posted by Barbara G. Goode, barbarag@pennwell.com, for BioOptics World.

Get All the BioOptics World News Delivered to Your Inbox

Subscribe to BioOptics World Magazine or email newsletter today at no cost and receive the latest news and information.

 Subscribe Now
Related Articles

NANOTECHNOLOGY/LIGHT ACTIVATION: IR light method turns blood clotting on (like drugs) and off (like nothing else)

Gold nanoparticles, controlled by infrared (IR) light from a pulsed femtosecond laser, promise to promote wound healing and help doctors control blood clotting in patients undergoing surgery.

Microscopy helps discover potential new drug target for cystic fibrosis

An international team of scientists, using automated microscopy and genetics, have discovered a promising potential drug target for cystic fibrosis.

Next-gen DNA sequencing helps provide new genetic clue to anorexia

The largest next-generation DNA sequencing study of anorexia nervosa to date has linked the eating disorder to variants in a gene coding for an enzyme that regulates cholesterol metabolism.

Synchrotron light identifies RNA double helix structure

Scientists at McGill University have crystallized a short RNA sequence, poly (rA)11, and used data collected at the Canadian Light Source (CLS) and the Cornell High Energy Synchrotron to confirm th...

BLOGS

Neuro15 exhibitors meet exacting demands: Part 2

Increasingly, neuroscientists are working with researchers in disciplines such as chemistry and p...

Why be free?

A successful career contributed to keeping OpticalRayTracer—an optical design software program—fr...

LASER Munich 2015 is bio-bent

LASER World of Photonics 2015 included the European Conferences on Biomedical Optics among its si...

White Papers

Understanding Optical Filters

Optical filters can be used to attenuate or enhance an image, transmit or reflect specific wavele...

How can I find the right digital camera for my microscopy application?

Nowadays, image processing is found in a wide range of optical microscopy applications. Examples ...

CONNECT WITH US

            

Twitter- BioOptics World

Copyright © 2007-2016. PennWell Corporation, Tulsa, OK. All Rights Reserved.PRIVACY POLICY | TERMS AND CONDITIONS