Bacteria can see, using their entire one-celled selves as a tiny camera lens to focus light, researchers reported Tuesday.
The ability goes beyond just a vague sense of where the light is, and allows the one-celled organisms to find just the right spot, the team reported in the journal eLife.
"The idea that bacteria can see their world in basically the same way that we do is pretty exciting," said Conrad Mullineaux of the University of Freiburg in Germany and Queen Mary University of London.
Mullineaux and an international team of colleagues studied a species of cyanobacteria that form a green slime on rocks in and near water.
People have known for a long time that these bacteria can move toward or away from light. And they photosynthesize light in much the same way that plants do.
The Mullineaux team worked on a microscopic level with the bacteria, shining lasers, watching their behavior and determining just how sensitive the bacteria actually are to light.
They found the bacteria are discriminating. They can find just the right amount of light that sustains life without burning them.
"Whenever one edge of a cell encountered the edge of the laser spot, the cell changed direction to move away from the laser illumination," they wrote.
"Spherical cyanobacteria are probably the world's smallest and oldest example of a camera eye."
They calculate that the bacteria can focus much like a human eye, although the image would be much blurrier.
"Our observation that bacteria are optical objects is pretty obvious with hindsight, but we never thought of it until we saw it," Mullineaux said.
"And no one else noticed it before either, despite the fact that scientists have been looking at bacteria under microscopes for the last 340 years."
Other bacteria probably do it, too, the researchers added.
Genome entrepreneur Craig Venter reported in 2004 that he had found genes in oceanic bacteria that are similar to the genes that control vision in people.