Why Euglena move like they do is a mystery that puzzled Antonie van Leeuwenhoek, known as the father of microbiology, more than three centuries ago. He was struck by the behaviour of these unicellular organisms, which he found in a drop of water from a nearby pond.

Today, the consensus amongst biologists studying Euglena is that metaboly is a functionless trait inherited through evolution from ancestors that used cell body deformations to eat other cells. However, to Marino Arroyo, a researcher at the Mathematical and Computational Modelling (LaCàN) research group of the Universitat Politècnica de Catalunya (UPC) and an adjunct researcher at the Institute for Bioengineering of Catalonia (IBEC), and to Italian scientists working on the research, this movement looked too purposeful to be a remnant of the past. This led them to begin joint research, and its results were published in the leading scientific journal Nature Physics under the title Swimming Euglena respond to confinement with a behavioural change enabling effective crawling.

The research was based on the hypothesis that metaboly could be useful for moving in crowded environments or narrow spaces, so they placed Euglena cells in increasingly narrow tubes to examine their behaviour. “Cells crawled with amazing elegance and effectiveness, at about one body length every twenty seconds, much faster than the fastest crawling animal cells”, states Giovanni Noselli.

Combining experimental observations, theoretical and computational models, the authors showed that the peristaltic body deformations of metaboly allow Euglena cells to push either on the confining walls or on the fluid surrounding them to move forward, making metaboly a particularly versatile and adaptable crawling mode.



The study also identified different kinds of metaboly in various species of Euglena, a fact that may have a significant impact on the field of biology. “Biologists may now ask the question of how these different styles fit into the evolutionary history of Euglena. More intriguingly, we now know that Euglena are the fastest crawling cells. However, if or when these cells use this ability in their natural environment remains unclear”, explains Marino Arroyo.

Inspiring new technologies
The results of this research demonstrate that Euglena cells operate following the principle of “embodied or mechanical intelligence”, a new paradigm according to which a soft robot can reliably respond to changing and complex requests by exploiting its flexibility, rather than relying on complex sensing and computations. “Euglena are single cells without a nervous system, and thus the intelligence they need to crawl and adapt to varying conditions can only be mechanical”, says Antonio DeSimone. The authors believe that soft robots inspired by Euglena could be devised in the future to move in complex and confined environments including soils, debris or even the human body.

This research was funded by the European Research Council.