This bacteria is actually a tiny eyeball
Joydeep/Wikimedia/Creative Commons

These bacteria are actually tiny eyeballs

Seeing is a complex task—so complex, in fact, that the human eye uses about 100 million light-sensitive cells to do it. But some single-celled bacteria can “see” using only one cell. According to new research, cyanobacteria in the Synechocystis genus use their entire bodies like lenses to track the location of a light source. Previously, researchers thought that these organisms, which use the sun for energy, migrate toward light by moving around at random and switching directions if their surroundings get darker. But today in the journal eLife, researchers report that the bacteria instead use their curved cellular surfaces to focus light from one direction onto their cell membranes on the opposite side, much like a camera lens focuses light onto the surface of film. The method was obvious when—staring through the lens of a microscope at a slide full of cyanobacteria—the researchers saw that each cell contained a tiny point of light in the same location, where the bacteria were focusing the source. The researchers were even able to trick the bacteria into moving in the opposite direction by shining a laser at them, mimicking the concentrated point of light that the bacteria create themselves. The size of the point suggests that Synechocystis can see at a resolution of nearly 20°—about a hundred times less precise than a human eye, but still impressive for a single-celled organism. Scientists say this light-focusing strategy may be widespread among bacteria. And given that cyanobacteria are some of the oldest organisms on Earth, it may also be among the earliest forms of sight.