Scientists solve a 50-year-old mystery – how do bacteria move?

Bacteria move forward by twisting the long, thread-like appendages into spiral shapes that act as makeshift fans.

University of Virginia scientists have solved a decades-old mystery.

researchers from University of Virginia The Medical School and their colleagues have solved a long-standing mystery of how E. coli and other bacteria move.

Bacteria move forward by twisting their long, thread-like ends into spiral shapes, which act as makeshift fans. However, because the “fans” are made up of a single protein, experts are baffled as to how exactly they do it.

The case was resolved by an international team headed by Edward H. The researchers used Cryo-EM technology and powerful computer modeling to reveal what no conventional optical microscope can see: the unusual structure of these propellers at the level of individual atoms.

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

Edward H.  Eagleman

Edward H. Eagleman, PhD, of the University of Virginia School of Medicine, and his collaborators have used cryo-electron microscopy to reveal how bacteria move — ending a more than 50-year mystery. Eagleman’s previous photographic work has seen him join the prestigious National Academy of Sciences, one of the highest honors a scientist can receive. Credit: Dan Addison | Virginia Communications University

Diagrams of bacteria’s ‘super-profiles’

Various bacteria contain one or more appendages known as flagella, or in the plural, flagella. A flagellum consists of thousands of subunits, all of which are identical. You might imagine that such a tail would be straight, or at least somewhat floppy, but it would keep the bacteria from moving. This is due to the fact that such forms cannot generate momentum. A rotating, switch-like fan is required to move the bacteria forward. Scientists call developing this shape “super-twisting,” and they now know how bacteria do it after more than 50 years of research.

Eagleman and colleagues discovered that the protein that makes up the flagellum can exist in 11 different states using cryo-EM. The shape of the key is shaped by a precise combination of these states.

The fan in bacteria is known to be quite different from similar fans used by single-celled cardiac organisms called archaea. Archaea are found in some of the most extreme environments on earth, such as in almost boiling ponds.[{” 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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