This is an article published in World Science News that cites evidence for the theory that some bacteria may have a sense of sight. It was written with the support of eLife.
How Slime Sees
(1) “The idea that bacteria can see their world in basically the same way that we do is pretty exciting,” said lead researcher Conrad Mullineaux, a biologist at Queen Mary University of London. “The fact that bacteria respond to light is one of the oldest scientific observations of their behavior,” he added. But the fact that they use their bodies as eyeballs, he said, though, is “pretty obvious with hindsight… we never thought of it until we saw it. 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.”
(2) His team of British and German researchers describes in the journal eLife how bacterial cells act as the equivalent of a microscopic eyeball or the world’s oldest, smallest camera eye.
(3) Cyanobacteria live in huge numbers in water bodies or can form a slippery green film on rocks. The species used in the study, Synechocystis, lives in freshwater lakes and rivers.
Cyanobacteria evolved an estimated 2.7 billion years ago. The fact that they can produce oxygen and convert carbon dioxide to organic material using energy from the sun—the process of photosynthesis—is thought to have caused mass extinctions and the oldest known ice age.
(4) As photosynthesis is crucial to these bacteria’s survival, scientists have sought to understand how they sense light. Previous studies have shown that they contain light-sensing molecules and that they can perceive and approach a light source, a process called phototaxis.
(5) The new study found they can do this because the cell body acts like a lens. As light hits the round surface, it refracts, or bends into a point on the other side of the cell. This triggers movement by the cell away from the focused spot. Within minutes, the microbe grows tiny tentacle-like things called pili that reach out towards the light. As they attach to the surface that they’re on, they retract and pull the bacteria along.
(6) Synechocystis serves as a spherical lens but the team thinks that rod-shaped bacteria can also trap light and sense the direction it is coming from using refraction, acting like an optical fiber.
(7) The scientists called the findings a likely example of convergent evolution—where two or more organisms evolve similar structures, but using different genetic means.
(8) “The physical principles for the sensing of light by bacteria and the far more complex vision in animals are similar, but the biological structures are different,” said co-author Annegret Wilde from the University of Freiburg in Germany.
(9) A Synechocystis cell is about half a billion times smaller than the human eye. As with the retina in the human eye, the image on the rear of the cell will be upside down. But its resolution will be much lower, so only a blurred outline of any object can be perceived. The ability of optical objects to distinguish fine detail is determined by “angular resolution.” In the human eye this is an impressive 0.02 degrees; in Synechocystis, an estimated 21 degrees.
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