Slime that can see: Bacterium acts like a single-cell eye

"We never thought of it until we saw it," said researcher Conrad Mullineaux.

By Brooks Hays
A diagram breaks down the differences between a human eyeball and the lens of a cyanobacterium cell. Photo by QMUL/eLife
A diagram breaks down the differences between a human eyeball and the lens of a cyanobacterium cell. Photo by QMUL/eLife

LONDON, Feb. 9 (UPI) -- A team of scientists from England and Germany have shown that bacteria see the world much like we do -- with eyes.

Of course, the "eyes" used by bacteria are much, much smaller and don't really produce images so much as detect light sources. But in crucial ways, a bacterium cell mimics the human eye.


"The idea that bacteria can see their world in basically the same way that we do is pretty exciting," lead researcher Conrad Mullineaux, a professor of microbiology at Queen Mary University of London, said in a news release.

Mullineaux and his colleagues looked at how cyanobacteria process and respond to light. Cyanobacteria are a type of algae-like bacteria that form thin layers of green slime on seaside rocks.

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According to the new research, published in the journal eLife, the bodies of bacterium cells double as a lens -- the world's smallest camera lens. As light passes through the cell body, it is refracted onto a point on the opposite side of the cell.

Almost immediately, the bacterium cells begin moving away from this focal point and toward the light. Soon, the cells sprout tentacle-like structures called pili in the direction of the light.


Researchers have long understood that bacteria respond to light, and scientists have been staring at bacterium cells under microscopes for centuries. Their discovery seems admittedly "obvious in hindsight."

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"We never thought of it until we saw it," Mullineaux said. "And no-one else noticed it before either."

Researchers say their discovery is an example of convergent evolution, whereby different organisms develop similar evolutionary adaptations. In this case, the gap between organisms -- single-celled and complex -- is rather large.

"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," added study co-author Annegret Wilde, a researcher at the University of Freiburg, in Germany.

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As is the case with must rudimentary vision systems, a bacterium eyeball creates a blurry image. It can focus light, but even if the cell had the capacity to process an image, the image wouldn't possess many details.

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