Clock-like ‘computer’ found inside brainless microscopic organism

Small, single-celled creatures apparently don’t have room for a brain that tells them how to move in complex ways, so they usually roll, slide, or swim to get around.

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But the microscopic inhabitants of the lake called Eurystomus euplotes mastered the brainless way of walking: Running like insects, with their 14 little appendages.

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They appear to move a bit like the Dutch kinetic sculptures called Strandbeasts, with watch-like connections running through them through a pattern of defined states that can adjust in response to the environment.

“There seemed to be this sequential logic going on with the movements,” says biophysicist Ben Larson of the University of California, San Francisco (UCSF), in a paper published in Current Biology. “They weren’t random and we started to suspect that some kind of information processing was going on.”

These protozoa – single-celled organisms with animal characteristics – have 14 bundles of individual cilia that work together like legs, called cirri. They can use these cirrus to swim and walk while actively hunting their prey.

Larson and his colleagues took microscopic images of these tiny predators to study their slow-motion movements. The researchers identified 32 different combinations of leg movements and found that certain combinations were more likely to be followed.

The cirrus are built of tubulin fibers, as well as the rest of the cellular structure of the scaffold (its cytoskeleton). These fibers also act as a support structure between the different cirri, so they also function as a type of mechanical communication.

“Euplotes uses these connections to facilitate elaborate walking movements,” explains UCSF biophysicist Wallace Marshall.

Computer modeling revealed that the tension in the fibers dictates which particular pattern of cirrus position is possible at any given time.

Some cirrus store stress in different phases of gait; when this stress is released, it forces the cell to progress to the next state, causing cyclical transitions between these states.

“The fact that Euplotes appendages move non-randomly from one state to another means that this system is like a rudimentary computer,” says Marshall.

When researchers exposed Euplote to a drug that disrupts the synchronous reactions of tubulin fibers, it disrupts the cell’s gait, causing the poor creatures to walk in futile circles.

His gait still remained regular, but it was no longer coordinated in a way that allowed for efficient movement. The mechanical connections between appendages could no longer be broken and re-established to make the cell work.

So instead of brains and nerves, these single-celled creatures are controlled by networks of signaling molecules. We have previously seen how these systems can achieve surprisingly complex behaviors in microbes, such as decision-making, learning, and maze navigation.

“This is a really fascinating biological phenomenon in its own right, but it can also highlight more general computational processes in other cell types,” says Larson.

There is still much to understand about the mechanistic workings of this locomotor system, but we can now add walking to the list of examples of how random molecular processes can be harnessed to produce sequential behaviors.

With information from Science Alert

Featured Image: Maple Ferryman/shutterstock

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