Scientists have been trying to figure out how it is possible for bacteria to perceive light and react to it ever since they started using microscopes 300 years ago. Now, an international team led by the University of Freiburg biologist Professor Annegret Wilde has solved this riddle. In studies on cyanobacteria, the researchers demonstrated that these tiny organisms of only a few micrometers in size move toward a light source using the same principle of the lens in the human eye. The study was published on Febraury 9, 2016 in the open-access journal eLife. The article is titled “Cyanobacteria Use Micro-Optics to Sense Light Direction.” Cyanobacteria have populated Earth for 2.5 billion years and can be found anywhere where there is light: in ice, deserts, rivers, and lakes, as well as in the walls of buildings and in aquariums. They use light to produce energy by the process of oxygenic photosynthesis. In the oceans, which cover roughly 70 percent of Earth's surface, oxygen-producing cyanobacteria are among the most important photosynthetically active organisms and are thus a central component of the biosphere. The Wilde group together with an international team discovered that cyanobacteria, which can move directly and precisely toward a light source, use their micro-optic properties to identify where the light is coming from. The light hits the surface of the round unicellular organisms, where it is focused as if by a microscopically tiny lens. This creates a focal point on the opposite side of the cell. The cells then move away from this point of high light intensity, causing them ultimately to move toward the natural light source.
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