It appears that bacteria can squeeze through practically anything. In extremely
small nanoslits they take on a completely new flat shape. Even in this squashed
form they continue to grow and divide at normal speeds. This has been demonstrated
by research carried out at TU
Delft's Kavli Institute of Nanoscience. The results will be appearing this
week in the online edition of the prestigious scientific journal Proceedings
of the National Academy of Sciences (PNAS) and as the cover article in the September
1 print issue of PNAS.
Using nanofabrication, Delft scientists made minuscule channels, measuring
a micrometer or less in width and 50 micrometer in length, on a silicon chip
between tiny chambers containing bacteria. Subsequently they studied the behaviour
of Escherichia. coli and Bacillus. subtilis bacteria in this artificial environment.
The bacteria were genetically modified so that they were fluorescent and could
easily be followed using a special microscope.
Squashed flat
Under normal circumstances these bacteria swim and this research showed that
they retain this motility in surprisingly narrow channels. They swam just as
actively as usual even in channels that were only 30 percent wider than their
own diameter (of about 1 micrometer). In even narrower submicron channels the
bacteria stopped swimming, and an unexpected effect took place: The bacteria
were able to make their way through ultra-narrow passageways in another manner,
that is by growing and dividing. The researchers found that this way, E. coli
bacteria could squeeze through narrow slits that were only half their own diameter
in width. Post-doctoral researcher, Jaan Männik: "This took us totally
by surprise. The bacteria become completely flattened. They have all sorts of
peculiar shapes both in the channels and when they finally come out at the other
side. What is really remarkable, however, is that in the channels, and therefore
under extreme confinement, they continue to grow and divide at normal speeds.
Apparently their shape is not a determining factor for these activities."
Subterranean bacteria, membrane filters and pacemakers
The flat bacteria form a new phenotype,. According to the researchers, this
form may be more common than one might think. The bulk of the biomass on Earth
is to be found under the ground. Here, bacteria often live in spaces that measure
around a micrometer. The study suggests that many more bacteria may be present
in small spaces than was always thought. This may have direct consequences,
for example for membrane filters (with tiny pores) for water treatment and for
medical applications, such as pacemakers or other implants, where bacteria must
be excluded as much as possible. The results of the study also provide more
fundamental understanding of the behaviour of bacteria that are 'locked up'
in nanosized environments.
Multidisciplinary
Little is known about the effect of this sort of confinement on the behaviour
of bacteria as yet. According to Prof. Cees Dekker, this has to do with the
required combination of very different disciplines: "Microbiologists do
not generally engage in nanofabrication, which enables us to examine this area
under controlled conditions, and nanoscientists usually know little about the
behaviour of bacteria. My colleague, Juan Keymer, an evolutionary biologist,
and I are now trying to combine these disciplines in our new Department of Bionanoscience.
And this is leading to all sorts of new discoveries."
The research results will be appearing in the week beginning 17 August in
the online edition of the scientific journal, Proceedings of the National Academy
of Sciences (USA). The article will also be featured as the cover article in
the print version of PNAS to be published on 1 September 2009.
Posted August 17th, 2009
