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Web address:
http://www.sciencedaily.com/releases/2008/08/
080821164308.htm
Some Cells Self-destruct For The Greater Common Good
enlarge
Salmonella bacteria (Salmonella typhimurium) in the mouse intestine. The
bacteria are green, the tissues of the mouse is blue and red. (Credit: Bärbel
Stecher/Wolf-Dietrich Hardt/ETH Zürich)
ScienceDaily (Aug. 22, 2008) — ETH Zurich biologists, led by Professors Martin
Ackermann and Wolf-Dietrich Hardt, in collaboration with Michael Doebeli of the
University of British Colombia in Vancouver (CN), have been able to describe
how random molecular processes during cell division allow some cells to engage
in a self-destructive act to generate a greater common good, thereby improving
the situation of the surviving siblings.
Survival strategy
The biologists investigated this unusual biological concept using the
pathogenic salmo-nella bacteria as an example. Diseases caused by salmonellae
are very unpleasant and even life-threatening. When contaminated food is
consumed – for example, egg-based foods or chicken and meat – salmonella
bacteria enter the gastro-intestinal tract where it triggers infection.
Vomiting and diarrhoea can last for days.
Normally, salmonellae grow poorly in the intestine because they are not
competitive with other bacteria of the gut. However, this dynamic changes if
salmonellae induce an in-flammatory response, namely diarrhoea, which
suppresses the other bacteria. The in-flammation is triggered by salmonellae
penetrating into the intestinal tissues. Once in-side, salmonellae is killed by
the immune system. This in turn creates a conflict: salmo-nellae are either
suppressed by the other bacteria in the gut, or die while trying to elimi-nate
these competitors.
As Ackermann, Hardt and Doebeli report, salmonellae have found a surprising
solution to this conflict. Inside the gut, the samonella bacteria forms two
groups that engage in job-sharing. A first group invades the tissue, triggers
an inflammation, then dies. A sec-ond group waits inside the gut until the
inactivation of the normal intestinal flora gives them an opportunity to
strike.This second group then multiplies unhindered.
Random processes and self-sacrifice
What determines whether an individual salmonella bacterium cell
self-sacrifices, or whether it will wait and benefit from the sacrifice of
others? The two groups are clones of the same genotype, so genetic differences
do not play a role. Rather, the difference between the two groups is a result
of random molecular processes during cell division. Cellular components are
randomly distributed between the two daughter cells with each cell receiving a
different amount. The resulting imbalance can be amplified and lead to
different properties of the clonal siblings.
In recent years it has been recognized that such random processes in a cell can
have a large influence on individual cells. The work by the ETH Zurich
researchers reveals a new biological explanation for this phenomenon. The two
salmonella phenotypes share their work, with the result being that they achieve
what a single phenotype on its own would not be capable of doing. This scenario
is fundamentally different from the usual explanations and presupposes that
individual phenotypes interact and have an effect on one another. The
self-sacrifice of phenotypes may be quite common among pathogenic bacteria, for
example, among the pathogens causing diarrhoea after antibiotic treatment
(clostridia) or pneumonia (streptococci).
Essential findings
Professor Ackermann says that "Random processes could promote job-sharing in
many different types of organisms." Many bacteria manufacture substances which
are toxic to their hosts but which are only released into the host environment
if the bacteria sacrifice themselves - if this is the sole method to get the
toxin out of the cell. This is why every cell makes a decision: toxin and death
or no toxin.
He stresses that it would not have been possible to study this theory so
thoroughly with-out the collaboration that took place among the three
specialist groups: Professor Hardt's group specialises in salmonella
infections; Professor Doebeli is a mathematician and theoretical biologist; and
Professor Ackermann's group focuses on phenotypic noise.
Journal reference:
1. Ackermann et al. Self-destructive cooperation mediated by phenotypic
noise. Nature, 2008; 454 (7207): 987 DOI: 10.1038/nature07067
Adapted from materials provided by ETH Zurich/Swiss Federal Institute of
Technology, via EurekAlert!, a service of AAAS.
Need to cite this story in your essay, paper, or report? Use one of the
following formats:
APA
MLA
ETH Zurich/Swiss Federal Institute of Technology (2008, August 22). Some Cells
Self-destruct For The Greater Common Good. ScienceDaily. Retrieved August 23,
2008, from http://www.sciencedaily.com /releases/2008/08/080821164308.htm
---------------
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