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Cyanobacteria Can See Like Humans!

In an attempt to determine how bacteria “see” their environment, a team of scientists from the UK and Germany have found that they do so in a similar manner to us. The microorganisms can perceive light and respond to it by using the same principle governing the function of the human eye lens. The paper is published in the journal eLife.

The light hits the round cells of the bacterium, where it is focused by a microscopically tiny lens. This creates a focal point on the opposite side of the cell. Credit: Nils Schürgers

Light hitting the round bacterial cells is focused by a tiny lens and refracted on the opposite side of the cells. Photo credits: Nils Schürgers.

The microscopic world, though naturally inconspicuous to us, has not remained unexplored. Researchers are forever looking into the organisms, their physiology, and ecology to learn more about them. With a similar goal in mind, a team of researchers found that bacterial cells can behave as a microscopic eyeball operating quite like a camera. Lead author Conrad Mullineux, a microbiologist from Queen Mary University of London, describes the concept of bacteria viewing their world very much like we do as “pretty exciting”.

Photo credits: eLife

The above image shows the similarities (and differences) among the camera, the human eye and the cyanobacteria. Photo credits: eLife

The experiment conducted by the scientists involved the species of cyanobacteria called Synechocystis that is found naturally in freshwater bodies. Its individual cell is around half a billion times smaller than a human eye. It is to be noted that cyanobacteria can be found in places where there is light, from ice to deserts to lakes; they are known to have the ability to move precisely and directly in the direction of a source of light. How are they able to do this?

“The fact that bacteria respond to light is one of the oldest scientific observations of their behaviour,” says Mullineaux.

“Our observation that bacteria are optical objects is pretty obvious with hindsight, but 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.”

The observations of the scientists reveal that the entire bacterium acts as a lens. Light hitting its spherical surface is focused by a “tiny lens”, and is refracted onto the other side of the cells such that the latter can move away from the focused spot towards the natural light source. Responding to the light, the bacteria use tentacle-like structures called pili to make the displacement towards its source.

The researchers explain that though the biological structures of the bacteria are different from animals’, the physical principles governing the sensing of light are similar for both.

As indicated in the diagram above, while the image on the opposite side of the bacterial cell will be upside cell as with the human retina, its resolution is much lower. This means that only a blurred outline of the object will be seen. The angular resolution (what allows optical objects to perceive fine details) in the human eye is 0.02 degrees while that of the Synechocystis is estimated to be 21 degrees. So, the bacteria can see like we do, but not as well as we do.

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