Bacteria move by twisting long, thread-like appendages into corkscrew shapes that act as makeshift propellers.
Scientists at the University of Virginia have solved a decades-long mystery.
researchers from University of Virginia School of Medicine and their colleagues have solved a long-standing mystery about how E. coli and other bacteria move.
Bacteria move forward by twisting their long, thread-like appendages into corkscrew shapes that serve as makeshift propellers. But since the “propellers” are made from a single protein, exactly how experts do it is met with confusion.
The problem was solved by an international team led by UVA’s Edward H. Egelman, a pioneer in the field of high-tech cryo-electron microscopy (cryo-EM). The researchers used cryo-EM and powerful computer modeling to reveal what no conventional light microscope could: the unusual structure of these propellers at the level of individual atoms.
“Although models of how these filaments can form such regularly coiled shapes have existed for 50 years, 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 show these models wrong, and our new understanding will help pave the way for technologies that can be based on such miniature propellers.”
from the University of Virginia School of Medicine, Ph.D. Edward H. Egelman and his colleagues used cryo-electron microscopy to reveal how bacteria can move – ending a mystery that lasted more than 50 years. Egelman’s previous imaging work saw him inducted into the prestigious National Academy of Sciences, one of the highest honors a scientist can receive. Credit: Dan Addison | Virginia University of Communication
“Supercoils” plans of bacteria
Different bacteria have one or more appendages known as flagellum or flagella in clusters. A flag is made up of thousands of sub-parts that are all identical. You would imagine that such a tail would be straight or at least somewhat flexible, but this would prevent the bacteria from moving. This is due to the fact that such forms cannot generate momentum. A spinning, plug-like propeller is needed to propel the bacterium forward. Scientists call the development of this form “supercoiling”, and after more than 50 years of research, they now know how bacteria do it.
Using cryo-EM, Egelman and colleagues discovered that the flagellar-forming protein can exist in 11 different states. The Tirbushka form is formed by the exact combination of these circumstances.
It turns out that the propeller in bacteria is completely different from similar propellers used by hearty single-celled organisms called archaea. Archaea are found in the most extreme environments on Earth, such as near-boiling pools of 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.
