New method studies living bacteria cells
ARGONNE, Ill. (Oct. 22, 2004) — Researchers at the U.S. Department of Energy's
Argonne National Laboratory have found a new way to study individual living
bacteria cells and analyze their chemistry.
In research published today in Science, the
scientists used high-energy X-ray fluorescence measurements for mapping and
chemical analyses of single free-floating, or planktonic, and surface-adhered,
or biofilm, cells of Pseudomonas
fluorescens. The results showed differences between the planktonic and
adhered cells in morphology, elemental composition and sensitivity to hexavalent
chromium, a heavy-metal contaminant and a known carcinogen. The biofilm cells
were more tolerant of the contaminant, while it damaged or killed the planktonic
cells.
In addition to determining the chemical differences between the cells, the
work also pioneers a potentially revolutionary new technique for investigating
microbiological systems in natural subsurface environments. This study advanced
the development of high-energy X-ray microprobes and methods for using the
microprobes to investigate single bacterial cells. The new capabilities
set the stage for future studies defining mineral-metal-microbe interactions
in contaminated environments.
“This technique also should be directly applicable to investigations of microbial
processes in extreme subsurface environments and to studies of a variety of
astrobiology topics, such as detection of past or present life in samples returned
from Mars, or determinations of the origins of life,” said lead author Ken
Kemner of Argonne's Environmental
Research Division.
No previously available techniques had the spatial resolution needed to analyze
individual bacterial cells noninvasively and nondestructively. Recent developments
at the Advanced Photon Source (APS) at
Argonne enabled the production of X-ray
beams small enough to probe single bacterial cells, which are typically one-hundredth
the diameter of a human hair. The APS provides the nation's most brilliant
X-rays for research.
In these experiments, scientists exposed both planktonic and biofilm
cells to elevated concentrations of hexavalent chromium. The researchers then
used X-ray fluorescence microscopy to measure the concentrations of elements
in individual cells before and after exposure to the heavy metal. The results
indicated that X-ray fluorescence analysis had distinguished living bacterial
cells from dead cells for the first time. The analysis also showed that a bone-like
mineral deposit had formed around the surface of the adhered cells. This deposit
made the adhered cells much more tolerant than planktonic cells to elevated
levels of the contaminant.
Next, the researchers used the energy tunability of the APS X-ray beamline
for spectroscopy experiments on the bacterial systems. These experiments showed
that the surface adherence of the biofilm cells promoted tolerance to the chromium
and reduced its toxicity level.
Finally, when the cells made the transition from the planktonic state to the
biofilm state, the scientists observed changes in the concentrations of many
transition metals required for bacterial life. These results suggest that X-ray
fluorescence analysis might be useful for determining whether a bacterial cell
is living or dead.
“No other technique has been capable of determining the metabolic state of
a single hydrated cell and the chemical speciation of metals on, in or near
a bacterial cell,” Kemner said. “The achievements of this study have the potential
to revolutionize the way scientists investigate mineral-metal-microbe systems.”
Other authors on the report, in addition to Kemner are Shelly D. Kelly, Edward
J. O'Loughlin and Deirdre Sholto-Douglas (Environmental Research Division,
Argonne); Barry Lai, Joerg Maser and Zhonghou Cai (Experimental Facilities
Division, Argonne); Mark Schneegurt (Wichita
State University); Charles F.
Kulpa, Jr. (University of Notre
Dame); and Kenneth H. Nealson (University
of Southern California).
Funding for this project came from the Natural and Accelerated Bioremediation
program of the U.S. Department of Energy's Office of Biological
and Environmental Research.
The nation's first national laboratory, Argonne National Laboratory conducts
basic and applied scientific research across a wide spectrum of disciplines,
ranging from high-energy physics to climatology and biotechnology. Since 1990,
Argonne has worked with more than 600 companies and numerous federal agencies
and other organizations to help advance America's scientific leadership and
prepare the nation for the future. Argonne is operated by the
University
of Chicago for the U.S. Department of
Energy's Office of Science.
For more information, please contact Donna Jones Pelkie (630/252-5501
or media@anl.gov) at Argonne.
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