World's Hardiest Life Form Explained

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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)

Now

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.

In food

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

water.

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

To

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

It

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.

One

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

Another

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.

"When the

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.

"There

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.

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