Bacteria may not be the most interesting of topics, but a recent discovery may suggest otherwise. Biologists have cracked the mystery of how a tiny bacterium senses light and moves towards it: the entire organism acts like an eyeball.
This was studied in single-celled pond slime, where the biologists observed how incoming rays of light are bent by the bacteria’s spherical surface and focused in a spot on the far side of the cell. By shuffling in the opposite direction to that bright spot, the bacteria moves towards the light. In the study, the cyanobacteria used live in water and harness their energy from photosynthesis. This makes sense when considering their enthusiasm for the sun. Scientists have hailed this as “the world’s smallest and oldest example” of a lens.
Co-author Professor Mullineaux from Queen Mary University commented that it was remarkable that no one had discovered this before, considering scientists have been observing bugs under microscopes for more than three centuries. It seems like even the tiniest of organisms are capable of making a big impact every once in a while.
To confirm this single-cell “vision”, Mullineaux worked with colleagues in the UK, Germany and Portugal on a series of experiments. They achieved this by using a laser beam to probe exactly how a focused light affects the organism’s behaviour. The laser beam was accurately aimed on the centre of a dish, while the team shone a bigger separate light on the Synechocystis cells from one side. As predicted, this tempted the bacteria across the surface, as they were pulling themselves towards the light using their tiny tentacles.
However, when the cells encountered the laser beam they “bounced off it”, as described by Professor Mullineaux. This demonstrates that when bright light is focused on one side of the bacterium it results in it running the other way.
There are some bigger single-celled organisms that are known to use clumps of photoreceptors, called “eyespots”, along with other cellular components to determine light direction. Despite this, the ability for Synechocystis to track light is seen as more remarkable, because the discovery is small and simplistic. After all, the best things do come in small packages.