Scientists Solve a 50-Year-Old Mystery: How Do Bacteria Move?

Cholera Bacteria Illustration
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Cholera bacteria illustration

The bacteria move forward by coiling long, threadlike corkscrew-like appendages that function as makeshift propellers.

Scientists at the University of Virginia have solved a decades-old mystery.

Researchers of the University of Virginia The School of Medicine and its colleagues have solved a long-standing mystery about how E. coli and other bacteria move.

The bacteria advance by coiling their long, threadlike corkscrew-like appendages, which serve as makeshift propellants. However, since the “helices” are made up of a single protein, experts don’t know exactly how they do it.

The case has been resolved by an international team led by Edward H. Egelman, Ph.D. from UVA, a pioneer in the high-tech field of cryo-electron microscopy (cryo-EM). The researchers used cryo-EM and powerful computer modeling to reveal what no traditional light microscope could see: the unusual structure of these helices at the level of individual atoms.

“While models have existed for 50 years for how these filaments could form such regular coiled shapes, we have now determined the structure of these filaments in atomic detail,” said Egelman, of UVA’s Department of Biochemistry and Molecular Genetics. “We can prove these models wrong, and our new understanding will help pave the way for technologies that could be based on such miniature propellers.”

Edward H. Egelman

Edward H. Egelman, Ph.D., of the University of Virginia School of Medicine, and his collaborators have used cryo-electron microscopy to reveal how bacteria can move, putting an end to a more than 50-year mystery. Egelman’s previous imaging work landed him in the prestigious National Academy of Sciences, one of the highest honors a scientist can receive. Credit: Dan Addison | University of Virginia Communications

Blueprints for Bacteria ‘Supercoils’

Different bacteria have one or more appendages known as flagella or, in the plural, flagella. A flagellum is made up of thousands of subunits, all identical. You imagine that tail would be straight, or at least somewhat flexible, but it would prevent bacteria from moving. This is due to the fact that such shapes cannot generate thrust. A corkscrew-like rotating propeller is required to move a bacterium forward. Scientists call developing this shape “supercoiling,” and now they know how bacteria do it after more than 50 years of research.

Egelman and colleagues found that the protein that makes up the flagellum can exist in 11 different states using cryo-EM. The corkscrew shape is formed by the exact combination of these states.

The bacterial helix is ​​known to be quite different from the similar helices used by the abundant single-celled organisms called archaea. Archaea are found in some of the most extreme environments on Earth, such as pools of near-boiling water.[{” attribute=””>acid, the very bottom of the ocean and in petroleum deposits deep in the ground.

Egelman and colleagues used cryo-EM to examine the flagella of one form of archaea, Saccharolobus islandicus, and found that the protein forming its flagellum exists in 10 different states. While the details were quite different than what the researchers saw in bacteria, the result was the same, with the filaments forming regular corkscrews. They conclude that this is an example of “convergent evolution” – when nature arrives at similar solutions via very different means. This shows that even though bacteria and archaea’s propellers are similar in form and function, the organisms evolved those traits independently.

“As with birds, bats, and bees, which have all independently evolved wings for flying, the evolution of bacteria and archaea has converged on a similar solution for swimming in both,” said Egelman, whose prior imaging work saw him inducted into the National Academy of Sciences, one of the highest honors a scientist can receive. “Since these biological structures emerged on Earth billions of years ago, the 50 years that it has taken to understand them may not seem that long.”

Reference: “Convergent evolution in the supercoiling of prokaryotic flagellar filaments” by Mark A.B. Kreutzberger, Ravi R. Sonani, Junfeng Liu, Sharanya Chatterjee, Fengbin Wang, Amanda L. Sebastian, Priyanka Biswas, Cheryl Ewing, Weili Zheng, Frédéric Poly, Gad Frankel, B.F. Luisi, Chris R. Calladine, Mart Krupovic, Birgit E. Scharf and Edward H. Egelman, 2 September 2022, Cell.
DOI: 10.1016/j.cell.2022.08.009

The study was funded by the National Institutes of Health, the U.S. Navy, and Robert R. Wagner. 

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