This release just in from The Swedish Research Council:
Got food poisoning? The cause might be bacterial spores, en
extremely hardy survival form of bacteria, a nightmare for health care
and the food industry and an enigma for scientists. Spore-forming
bacteria, present almost everywhere in our environment, can also cause
serious infectious diseases, such as tetanus, anthrax, and botulism.
Anthrax Spores (NIST)
researchers from Lund University in Sweden and the U.S. have made a
breakthrough in our understanding of the molecular characteristics of
spores that in the long term may lead to new methods for sterilizing
food and medical equipment. The findings are published in the latest
issue of the American scientific journal PNAS.
production and health care, high temperatures are used to kill spores,
which can survive boiling and normal disinfectants. But this is costly,
and it depreciates the nutritional value and the taste of food. Why
spores are so resistant to heat and how they can survive without
nutrients has long puzzled researchers, but it has been suspected that
what may be crucial are changes in the physical properties of spore
But now physical chemists at the Lund University Faculty
of Engineering, in collaboration with microbiologists from Lund and the
U.S., have succeeded in "seeing" the water in intact spores and
discovered that it has entirely different properties than scientists
previously thought. They have also seen that the proteins in the spores
are immobile, which explains why spores can withstand such high
temperatures. Thirdly, they saw that the core membrane of a spore
constitutes an effective barrier for the water, which supports the
hypothesis that it protects the spore DNA from toxic compounds. To be
able to "see" what happens inside spores, the Lund researchers
developed a unique method.
How spores function
survive long periods without nutrients or other adverse conditions,
certain types of bacteria have developed the ability to form spores,
where the cell's DNA and necessary enzymes are packed into a capsule
surrounded by multiple protective barriers. In this form the bacteria
can survive for hundreds, perhaps millions, of years in a dormant state
and, what's more, endure drought, extreme temperatures, radiation, and
toxins that would quickly knock out unprotected bacteria. But spores
read their surroundings, and as soon as conditions improve, they
transform back into active bacteria.
Water in spores and bacteria is highly fluid
has long been known that the ability of spores to survive has to do
with the low water content in the spore core, where the bacterial
cell's DNA and most enzymes are stored. Many scientists previously
thought that this water was transformed to a solid state, a so-called
glass. This glass would protect the enzymes and lock down all cell
machinery. This seems to be what happens in other hardy life forms,
such as plant seeds.
"What we have discovered is that the water
in the spore is nearly as fluid as in regular bacteria, while the
enzymes are largely immobile. We therefore think that spores' heat
resistance and ability to shut down their cell machinery can be
ascribed to the fact that certain critical enzymes do not function in
the low water content in the spore core. But much more work is needed
to figure out the details of the mechanism," explains Bertil Halle,
professor of physical chemistry, who, together with Erik Sunde, a Ph D
student in his research group, wrote the PNAS article "The Physical
State of Water in Bacterial Spores."
According to Bertil Halle,
the findings should be seen in the light of a fifty-year-long debate
about water in bacteria and other cells, where many researchers have
maintained that the cell water has completely different properties than
water in the test-tube solutions that are normally used to study
proteins and other biomolecules.
"This is an extremely important
issue that touches on all life. If these scientists were right, then
much of what we have learned from test tube experiments about proteins,
for instance, would have limited relevance," says Bertil Halle.
reason the research world has been divided for such a long time is that
there has been no method to allow us to see the water in cells or, what
is even more difficult, in spores. But over the last fifteen years the
Lund group has developed a technique called magnetic relaxation
dispersion that can do this.
By varying the magnetic field, the
scientists can see how molecules move on time scales from one
thousandth to one billionth of a second. Using their unique method, the
Lund team has performed several pioneering studies of proteins, DNA,
and living bacterial cells, including two that were published in PNAS
on April 29, 2008.
A tightly encapsulated core with immobile proteins explains the hardiness of spores
important observation crucial to understanding why spores can survive
temperatures up to 150 degrees centigrade is that the proteins in the
spore do not move freely, as in a water solution.
temperature rises, protein molecules unfold into long chains. Since the
molecules in the spore core are immobilized, they don't get tangled up
with each other, as they would in ordinary cells. When the temperature
goes down, they fold up again, and no damage has been done to the
cell," explains Erik Sunde.
In their experiments the researchers
have also been able to see that the membrane of the spore core lets
water through at a rate that is at least a hundred times slower than
for a bacterial cell membrane. This compact inner barrier protects the
spore from toxic molecules that otherwise might destroy the spore's DNA.
are so many other things we still have to learn about structures and
processes inside living cells. Almost everything we know about proteins
comes from test tube experiments, but in the special environment inside
a cell, partially different phenomena may occur. A molecular
understanding of the structure and dynamics of cells is important, not
least for the development of new drugs," says Erik Sunde.