The world's smallest life form can now move, thanks to genetic engineering

The synthetic bacterium can now swim.
Ayesha Gulzar
Microscopic view of spiroplasma bacteria
Microscopic view of spiroplasma bacteria

UA/Wikimedia Commons 

In a breakthrough study, Japanese researchers at Osaka Metropolitan University have engineered the smallest motile life form ever. They introduced seven bacterial proteins into a synthetic bacterium, allowing it to move independently.

The research provides a better understanding of evolution and the origins of motility.

The rise of synthetic biology

The new study is based on the synthetic bacterium called syn-3. The tiny spherical bacteria contain minimal genetic information, allowing them to grow and divide without motility.

The team experimented with syn-3 by introducing seven genes that code for proteins that are likely involved in the swimming motion of Spiroplasma bacteria. Spiroplasma is a small natural bacterium with a long helix shape. The bacterium is known to “swim” by essentially reversing the direction of its helix.

After adding these proteins, the syn-3 changed from its usual round form to the same helix shape as Spiroplasma, and most importantly, it was now able to swim using the same technique.

“Our swimming syn3 can be said to be the ‘smallest mobile lifeform’ with the ability to move on its own,” said Professor Makoto Miyata, co-lead author of the study. “The results of this research are expected to advance how we understand the evolution and origins of cell motility."

"Studying the world’s smallest bacterium with the smallest functional motor apparatus could be used to develop movement for cell-mimicking microrobots or protein-based motors.”

The researchers also wanted to see how the expression of different combinations of the motility genes would affect the genetically engineered bacteria to swim. In doing so, they found that the expression of only two proteins was necessary for promoting motility in syn-3, likely indicating that many of the proteins were redundant and demonstrating a minimal system for motility.

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A proof of concept

The world's smallest life form can now move, thanks to genetic engineering
Microscope images of natural Spiroplasma, the synthetic bacteria syn3, and mobile syn3

Although this study is primarily a proof of concept, the research helps answer the quintessential questions about the earliest life forms and genomes involved in their mobility. The acts of running, swimming, sprawling, or moving all can be dated back to cellular movement, but how these organisms adapted these movements during evolution has been a mystery. Genetic engineering might help shed light on this area of research that has been eluding scientists.

“Our swimming syn3 can be said to be the ‘smallest mobile lifeform’ with the ability to move on its own,” said Professor Miyata. “The results of this research are expected to advance how we understand the evolution and origins of cell motility.”

The team believes the study of this bacterium will also allow scientists to create micro and nanorobots that require the most basic motor functions to move. “Studying the world’s smallest bacterium with the smallest functional motor apparatus could be used to develop movement for cell-mimicking microrobots or protein-based motors”

The study, which was published in Scientific Advances, is the result of a collaboration between graduate student Hana Kiyama from the Graduate School of Science at Osaka City University and Professor Makoto Miyata from the Graduate School of Science at Osaka Metropolitan University.

Abstract:

Motility is one of the most important features of life, but its evolutionary origin remains unknown. In this study, we focused on Spiroplasma, commensal, or parasitic bacteria. They swim by switching the helicity of a ribbon-like cytoskeleton that comprises six proteins, each of which evolved from a nucleosidase and bacterial actin called MreB. We expressed these proteins in a synthetic, nonmotile minimal bacterium, JCVI-syn3B, whose reduced genome was computer-designed and chemically synthesized. The synthetic bacterium exhibited swimming motility with features characteristic of Spiroplasma swimming. Moreover, combinations of Spiroplasma MreB4-MreB5 and MreB1-MreB5 produced a helical cell shape and swimming. These results suggest that the swimming originated from the differentiation and coupling of bacterial actins, and we obtained a minimal system for motility of the synthetic bacterium.

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