CAU - Universität Kiel
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Nr. 84, 10.10.2015  voriger  Übersicht  weiter  REIHEN  SUCHE 

Health versus disease: an evolutionary arms race

Kiel scientists present a new study on the coevolution between host and pathogens. Their results not only shed a new light on evolutionary dynamics, but may also lead to more sustainable treatment strategies in the future.

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

Every year, new flu germs emerge, and life-threatening diseases such as Ebola cause global concerns at regular intervals. To achieve better understanding of the underlying disease epidemics, research into the adaptability and thus the evolution of the infectious pathogens is necessary. Scientists at the Department of Evolutionary Ecology and Genetics at Kiel University have now been able to gain important new insights: With the help of innovative experiments in the lab, they examined extremely rapid, mutual adaptations of host and pathogen. Their new findings on this so-called coevolution of host and pathogen might be of value to improve understanding understanding of related human diseases in the future.

The research team of Professor Hinrich Schulenburg, member of the research focus “Kiel Life Science”, used a special experimental model system, consisting of the nematode worm Caenorhabditis elegans as a host and the bacterium Bacillus thuringiensis as a pathogen, to follow evolution in real-time. The core of the study was an evolution experiment under controlled conditions in the lab, which was combined with the characterization of the evolved genetic mechanisms and specific traits in both the worm and the bacterium. “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 during coevolution be tween host and pathogen,” emphasizes Schulenburg.

The research relied on a fruitful collaboration between the Schulenburg lab and research groups at the Institute of Clinical Molecular Biology (ICMB) at Kiel University and at the universities of Münster, Göttingen, Osnabrück and Tübingen, and yielded two important new insights: the first is that virulence and thus the ability of the pathogen to damage or kill the host only provides an evolutionary advantage during coevolution. Dr Leila Masri, former member of the Schulenburg Lab and now postdoctoral researcher at the Institute of Science and Technology Austria, explains: “We were astonished that 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 produce any counter- adaptations, the pathogen can lose its ability to harm the host. 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 amount of this poison is linked to a certain genetic characteristic of the bacterium which is favoured during evolutionary adaptation to the host. These results demonstrate that ongoing coevolution can shape the specific characteristics of the genome and thus central aspects of the biology of the pathogen.

Further research is still required before the current findings can be applied to human disease. They may nevertheless suggest that an increase in selective pressure on the pathogen can enhance its harmful potential. The increased use of antibiotics, for example, promotes the spread of resistant pathogens and ultimately aggravates disease progression. The Kiel researchers are convinced that a different strategy is worth consideration: Instead of aiming at pathogen elimination, it may be more efficient to promote tolerance of the host to the disease agent. This could prevent an escalating arms race on the pathogen side and thus represent a more sustainable treatment strategy to cope with infectious disease.

Christian Urban
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