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Press release No. 194/2015, 2015-06-04 | zur deutschen Fassung | print version | Search

Live from the Evolution Lab

Study on coevolution between host and pathogens sheds new light on evolutionary dynamics

Every year, new cold and flu pathogens occur and problematic pathogens such as Ebola cause global alarm at regular intervals. The key to a better understanding of disease epidemics lies in the adaptability and thus in the evolution of the pathogens that cause disease. With the aid of innovative experiments in the lab, researchers in the research group Evolutionary Ecology and Genetics at Kiel University (CAU) have now been able to gain important insights into the evolution of pathogens. To do this they examined extremely rapid, mutual adaptations of host and pathogen. The Kiel scientists have now published their results in the current edition of the prominent scientific journal PLOS Biology.

With the aid of a model system, the research team was able to observe evolution at work. They identified the underlying genetic mechanisms and the concrete features subject to selection pressure in the host and the pathogens. In long years of collaboration with research groups at the Institute for Clinical Molecular Biology (IKMB) at the CAU and at the universities of Münster, Göttingen, Osnabrück and Tübingen, the researchers of the CAU working group Evolutionary Ecology and Genetics carried out experiments on the mutual adaptations between the model host used (the thread worm Caenorhabditis elegans) and a model pathogen (the bacterium Bacillus thurigiensis). "We were able to precisely control the extent of the mutual adaptations and thus the coevolution in the lab. This provided us with the ultimate test to find out what really happens in the coevolution between host and pathogen," emphasizes Professor Hinrich Schulenburg, leader of the research group Evolutionary Ecology and Genetics and member of the excellence cluster Inflammation Research.

The now published results indicate two important new findings: the first is that pathogens only receive an evolutionary advantage during coevolution if they are virulent, i.e. if they are able to damage or kill the host. Dr. Leila Masri, lead author of the study, explains: "We were astonished that the virulence is only maintained when there is the corresponding evolutionary counter-response of the host, so that an evolutionary arms race occurs." If the host does not display any counter-adaptations, the pathogen can lose its virulence.

Secondly, the Kiel scientists were able to demonstrate that the bacteria achieve their high virulence by increased production of a toxic substance that damages the host. The increased occurrence of the toxin is linked to a certain genetic characteristic of the bacterium which asserts itself under the pressure of the mutual adaptation. "Our results prove that constant coevolution leads to a specific characteristic of the genome and thus of all biological characteristics of the pathogen," continues Dr. Masri.

The present study is unprecedented in terms of its complexity. It is based on a comprehensive research approach in which evolution experiments are combined with genome sequencing, genetic analyses and extensive mathematical and statistical studies to allow a complete inventory of the complex adaptations between the interaction partners. An advantage in the observation of these interactions is that the evolutionary adaptations in the host and pathogen develop within just a few generations.

The Kiel scientists see a need for further research into the question as to how the new findings can be applied to fighting pathogens. Provisional research results indicate that an artificially increased evolutionary pressure – for example using antibiotics – can lead to increased harmfulness of the pathogens. According to Professor Schulenburg, in order to counteract this development a different strategy is necessary: "Instead of the extermination of the pathogen, it should be aimed at the tolerance of the host to the pathogen." This and similar questions on the adaptability of pathogens are currently an important focus of the new research area "Kiel Life Science" at the University of Kiel. The now published research work was also part of the nationwide priority program "Host-Parasite Coevolution" of the German Research Foundation (DFG).

Original work:
Leila Masri, Antoine Branca, Anna E. Sheppard, Andrei Papkou, David Laehnemann, Patrick S. Guenther, Swantje Prahl, Manja Saebelfeld, Jacqueline Hollensteiner, Heiko Liesegang, Elzbieta Brzuskiewicz, Rolf Daniel, Nicolaas K. Michiels, Rebecca D. Schulte, Joachim Kurtz, Philip Rosenstiel, Arndt Telschow, Erich Bornberg-Bauer, Hinrich Schulenburg (2015): Host-Pathogen Coevolution: The Selective Advantage of Bacillus thurigiensis Virulence and its Cry Toxin Genes, PLOS Biology

Prof. Hinrich Schulenburg
Research group Evolutionary Ecology and Genetics,
Zoological Institute, Kiel University
Tel: 0431-880-4141

Further information:
Research group Evolutionary Ecology and Genetics, Zoological Institute, Kiel University

Research focus "Kiel Life Science", Kiel University

DFG Priority Program "Host-Parasite Coevolution":

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The lead author of the study, Dr. Leila Masri, working in the lab of the research group Evolutionary Ecology and Genetics at the University of Kiel.
Photo: Hinrich Schulenburg, Kiel University

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Microscopic photograph of the thread worm Caenorhabditis elegans with the red-stained bacteria inside it.
Photo: Andrei Papkou, Hinrich Schulenburg, Kiel University

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The thread worm Caenorhabditis elegans is ideal as a model organism in evolutionary biology.
Photo: Antje Thomas, Hinrich Schulenburg,
Kiel University

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No escape: As the worms were able to avoid the bacteria in a normal Petri dish, the Kiel researchers cultivated host and pathogen in glass Christmas balls.
Photo: Hinrich Schulenburg, Kiel University

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