Slime can see

http://www.eurekalert.org/pub_releases/2016-02/e-scs020716.php

Public Release: 9-Feb-2016
Slime can see
Scientists discover that slime-forming bacteria act as optical objects
eLife

After more than 300 years of looking, scientists have figured out how bacteria "see" their world. And they do it in a remarkably similar way to us.

A team of British and German researchers reveal in the journal eLife how bacterial cells act as the equivalent of a microscopic eyeball or the world's oldest and smallest camera eye.

"The idea that bacteria can see their world in basically the same way that we do is pretty exciting," says lead researcher Conrad Mullineaux, Professor of Microbiology from QMUL's School of Biological and Chemical Sciences from Queen Mary University of London (QMUL).

Cyanobacteria are found in huge numbers in water bodies or can form a slippery green film on rocks and pebbles. The species used in the study, Synechocystis, is found naturally in freshwater lakes and rivers. Cyanobacteria evolved around 2.7 billion years ago and the fact that they are able to produce oxygen and fix carbon dioxide using energy from the sun - photosynthesis - is thought to have caused mass extinctions and the oldest known ice age.

As photosynthesis is crucial to the survival of these bacteria, scientists have sought to understand how they sense light. Previous studies have shown that they contain photosensors and that they are able to perceive the position of a light source and move towards it, a phenomenon called phototaxis.

The current study reveals that they are able to do this because the cell body acts like a lens. As light hits the spherical surface, it refracts into a point on the other side of the cell. This triggers movement by the cell away from the focused spot.

Within minutes, the bacteria grow tiny tentacle-like structures called pili that reach out towards the light source. As they attach to the surface that they're on, they retract and pull the bacteria along.

"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," he says.

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