Heidelberg Researchers Elucidate Distribution of Ions on Bacterial Surfaces
4 November 2010
Physicists working at Heidelberg University have published new research findings on the subject of ions on bacterial surfaces. The scientists from the Institute of Physical Chemistry were able to determine the quantity of ions and their distribution on a bacterial membrane lipid surface. This is a first step towards future systematic investigation of the impact of ions on the interaction between bacteria and various biomolecules. Detailed understanding of the role of such ions is important for medicine, e.g. for the development of antibiotics on the basis of small molecules, so-called peptides. The findings have been published in the science journal PNAS.
Bacterial interactions with various biomolecules have long been a subject of intensive research. Antimicrobial peptides can kill bacteria, but the presence of certain ions, e.g. calcium ions, protects the bacteria from this attack. Given the electric charge most bacteria carry on their surfaces, electrostatics plays a crucial role in this interaction. As ions dissolved in water shield off some of the electrostatic forces, the interactions between bacterial surfaces and ions are a topic of major significance.
With their scientific supervisor Prof. Dr. Motomu Tanaka, PhD students Emanuel Schneck and Thomas Schubert were able to determine precisely the quantity and distribution of different sorts of ions. They did so via X-ray fluorescence measurements at the European Synchrotron Radiation Facility (ESRF) in Grenoble with the collaboration of Dr. Oleg Konovalov. The researchers illuminated a layer of bacterial membrane lipids, known as lipopolysaccharides, at an air-water interface with an X-ray beam at small angles of incidence. Initially, this stimulated only the ions near the surface to emit fluorescence, the emission of characteristic electromagnetic radiation. Increasing the angle of incidence enlarged the area in which fluorescence stimulation took place. From the angle-dependence of the intensity of fluorescence the scientists were able to precisely reconstruct the distribution of ions.
In quantitative terms, these observations agree with the computer simulations done by the Canadian scientists Prof. Dr. David Pink and Bonnie Quinn at St. Francis Xavier University in Antigonish. Also involved in the research work were Prof. Dr. Thomas Gutsmann and Prof. Dr. Klaus Brandenburg at the Research Center Borstel, the Leibniz Center for Medicine and Biosciences. In a procedure especially designed for the purpose, they prepared the lipopolysaccharides as a model system.
For more information, go to www.pci.uni-heidelberg.de/bpc2/index.html .
E. Schneck, T. Schubert, O. Konovalov, B. Quinn, T. Gutsmann, K. Brandenburg, D. Pink, M. Tanaka: Quantitative determination of ion distributions in bacterial lipopolysaccharide membranes by grazing-incidence X-ray fluorescence, PNAS 2010, 107 (20), 9147-9151, doi: 10.1073/pnas.0913730107
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