World's fastest creature may also be one of the smallest

August 8, 2018 by John Toon, Georgia Institute of Technology
Single-celled protozoan. With support from the National Science Foundation, Georgia Tech researchers are studying Spirostomum ambiguum, a tiny single-celled protozoan that achieves blazing-fast acceleration while contracting its worm-like body. Credit: Rob Felt, Georgia Tech

Ask most people to identify the fastest animal on Earth and they'll suggest a cheetah, falcon or even a sailfish. To that list of speedy animals, Georgia Institute of Technology assistant professor Saad Bhamla would like to add the Spirostomum ambiguum, a tiny single-celled protozoan that achieves blazing-fast acceleration while contracting its worm-like body.

Common to many lakes and ponds, the Spirostomum ordinarily moves about using tiny hairs called cilia. But its claim to speed involves extremely rapid acceleration while contracting its body when startled. The creature can shorten its body by more than 60 percent in a few milliseconds, going from a four-millimeter flat ribbon to the shape of an American football – all without the kind of muscles humans use. 

How it does that, and how it does that without damaging fragile internal structures, is part of a four-year National Science Foundation (NSF) grant Bhamla just received. The physics and mathematics of the answers could help advance nanotechnology and accelerate a new generation of robots barely large enough to see with the naked eye.

"As engineers, we like to look at how nature has handled important challenges," said Bhamla, who is an assistant professor in Georgia Tech's School of Chemical and Biomolecular Engineering. "We are always thinking about how to make these tiny things that we see zipping around in nature. If we can understand how they work, maybe the information can cross over to fill the gap for small robots that can move fast with little energy use."

Human muscles rely on the activity of actin and myosin proteins, but tiny creatures like this protozoan owe their motion to supramolecular springs, latches and motors that more often are found in the mechanical world. 

"If they had only the actin and myosin proteins that make up our muscles, they couldn't generate enough force to actually move that fast," Bhamla added. "The smaller they are, the faster they go – up to 200 meters per second squared. That's really off the charts."

Bhamla holds a Ph.D. in chemical engineering from Stanford University, where he was part of a research team studying the world of very small animals. The single-celled creatures he and his collaborators found in ponds and lakes challenged his expectations for what it means to be unicellular.

What is the fastest animal on the planet? Cheetah? Falcon? Sailfish? Georgia Tech assistant professor Saad Bhamla would like to add the Spirostomum ambiguum to the list. Spirostomum is a tiny single-celled protozoan that achieves blazing-fast acceleration while contracting its worm-like body. Credit: Georgia Institute of Technology
"My early biology training suggested that cells were just simple bags of fluid that didn't do much but make up more interesting tissues," said Bhamla. "The Spirostomum is completely different from the cells we are accustomed to."

As part of the NSF's joint molecular cell biology (MCB) and Physics of Living Systems (POLS) program, Bhamla and his students are using the language of mathematics and physics to describe the activities of Spirostomum. 

"For instance, we want to know what is the fundamental limit for acceleration in a living cell," he said. "We want to map out everything this creature is doing and model it in the computer, taking an engineering approach. We want to learn how a single cell achieves such remarkable acceleration and uses molecular springs to amplify its power output."

What the researchers learn could be useful to future generations of tiny robots that won't be able to utilize the technologies for propulsion and grasping common to much larger machines. Beyond the simple mechanical challenges of making very small robots, engineers will have to confront energy density limitations – which the Spirostomum seems to have overcome.

Robots this small would also be rather fragile, but what the researchers have observed by peering at protozoans is just the opposite. 

"It has internal organelles, DNA and delicate cytoskeletal components inside," Bhamla noted. "We want to understand how they are not damaged by the rapid compression, because the internal pressures must increase rapidly. This may advance our understanding of how truly robust biological materials are under extreme stresses and pressures. "

Protozoans like Spirostomum are found everywhere in bodies of water, and part of the NSF award will fund sharing that tiny world with K-12 students. Already, Bhamla has established a collaboration with Janet Standeven, a science teacher  at the Lambert High School in Forsyth County, north of Atlanta. Five high school students are working this summer in a Georgia Tech lab to learn more about the world of tiny organisms.

"To find these curious and crazy cells, you don't need to go far," said Bhamla. "We just go to a pond, collect samples and look them under a microscope. The sky is the limit on how far you can push this, and are capable of a lot given the right mentorship."

Explore further: New insights into human tears could improve contacts lenses

Related Stories

New insights into human tears could improve contacts lenses

March 23, 2016

When contact lenses work really well, you forget they are on your eyes. You might not feel the same at the end of a long day staring at a computer screen. After too many hours of wear, the lenses and your eyes dry out, causing ...

Engineers stop soap bubbles from swirling

September 13, 2016

The spinning rainbow surface of a soap bubble is more than mesmerizing – it's a lesson in fluid mechanics. Better understanding of these hypnotic flows could bring improvements in many areas, from longer lasting beer foam ...

Iimproved integration of living muscles into robots

May 30, 2018

The new field of biohybrid robotics involves the use of living tissue within robots, rather than just metal and plastic. Muscle is one potential key component of such robots, providing the driving force for movement and function. ...

Recommended for you

Activating a new understanding of gene regulation

November 19, 2018

Regulation of gene expression—turning genes on or off, increasing or decreasing their expression—is critical for defining cell identity during development and coordinating cellular activity throughout the cell's lifetime. ...

Geneticists solve long-standing finch beak mystery

November 19, 2018

Bridgett vonHoldt is best known for her work with dogs and wolves, so she was surprised when a bird biologist pulled her aside and said, "I really think you can help me solve this problem." So she turned to a mystery he'd ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Iochroma
not rated yet Aug 08, 2018
Well, if the action is only contraction, and that is on a nano-scale. who cares how fast they curl up?
Whart1984
Aug 11, 2018
This comment has been removed by a moderator.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.