Researchers develop technique for bacteria crowd control
ARGONNE, Ill. (April 16, 2007) – A surprising technique to concentrate, manipulate
and separate a wide class of swimming bacteria has been identified through
a collaboration between researchers at the U.S. Department of Energy's Argonne
National Laboratory, Illinois Institute of technology, University of Arizona
at Tucson and Cambridge University, U.K. This device could have enormous applications
in biotechnology and biomedical engineering, including use in miniaturized
medical diagnostic kits and bioanalysis.
The technique is based on the transmission of tiny electric current in
a very thin film sample cell containing a colony of bacteria. The current produces
electrolysis that changes the local pH level in the vicinity of the electrodes.
The bacteria, uncomfortable with the changes in pH, swim away from the electrodes
and ultimately congregate in the middle of the experimental cell. Concentrated
bacteria form self-organized swirls and jets resembling vortices in vigorously
stirred fluid.
The method, which is suitable for flagellated bacteria such as E. coli, Bacillus
subtilis, among many others, relies on the ability of bacteria to swim
toward areas of optimal pH level. The bacteria live in an environment
of a specific pH level, so that an increase or decrease of pH stimulates the
bacteria to avoid areas of non-comfortable pH and swim in the direction of
pH gradient. The researchers used an electric current to create a controlled
deviation of the pH levels from the bulk values. Since only living bacteria
respond to the pH stimulation, using this method can separate living and
dead cells or bacteria with different motility.
The device, capable to change the thickness of a film from 1mm to 1 micron
(with accuracy of 5 percent) and control the position of electrodes, is intended
to separate and concentrate small quantities of living and dead microorganisms
in confined spaces. It can be used for the purposes of express bioanalysis,
diagnostic and identification of small bacterial samples, and separation sicken/live
cells. A patent for the device is currently pending.
“Using this method, our research succeeded in dramatically increasing the concentration
of microorganisms in tiny fluid drops and films. Unlike traditional centrifuging
techniques, the new approach allows selective concentration of healthy cells,” said
Andrey Sokolov, Ph.D. student from Illinois Institute of Technology and contributor
to the research.
In addition to the development of the device used in the experimentation,
research findings uncovered the explanation for the long-standing fundamental
questions on the properties of collective and organized motion in the systems
of interacting self-moving objects. Besides swimming bacteria, other examples
include bird flocks, fish schools, motor proteins in living cell, and even
swarms of communicating nano-robots.
“We have presented experimental studies of collective bacterial swimming in thin
fluid films where the dynamics are essentially two-dimensional and the concentration
can be adjusted continuously,” explained Igor Aronson, physicists at Materials
Science Division, Argonne National Laboratory. “Our results provide strong evidence
for the pure hydrodynamic origin of collective swimming, rather than chemotactic
mechanisms of pattern formation when microorganisms just follow gradients of
a certain chemical, such as nutrient, oxygen, or other.”
Detailed results of these findings have been published in Physical Review
E and in Physical Review Letters.
Funding for this research was provided by the U.S. Department of Energy's
Office of Basic Energy
Science.
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For more information, please
contact Steve McGregor (630/252-5580 or media@anl.gov)
at Argonne.
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