Bacteria propagate themselves by wrapping long, threadlike appendages into corkscrew forms that act as temporary propellers.
University of Virginia scientists have solved a decades-old mystery.
Researchers University of Virginia The School of Medicine and colleagues have solved a long-standing mystery about how E. coli and other bacteria move.
Bacteria propagate by wrapping their long, filamentous appendages into corkscrew shapes that act as makeshift propellers. But because the “propellers” are made up of a single protein, experts are confused about exactly how they do it.
The case is with Edward H. Egelman, Ph.D. of UVA, a pioneer in high-tech cryo-electron microscopy (cryo-EM). solved by an international team led by Cryo-EM and powerful computer modeling were used by the researchers to reveal what no conventional light microscope could see: the unusual structure of these propellers at the level of individual atoms.
“While models have existed for 50 years for how these filaments can form such regular helical shapes, we have now determined the structure of these filaments in atomic detail,” said Egelman of the UVA Department of Biochemistry and Molecular Genetics. “We can show these models are wrong, and our new understanding will help pave the way for technologies that could be based on such miniature propellers.”
Edward H. Egelman, PhD, of the University of Virginia School of Medicine and his collaborators used cryo-electron microscopy to reveal how bacteria can move, ending a more than 50-year mystery. Egelman’s previous imaging work has seen him gain admission to the prestigious National Academy of Sciences, one of the highest honors a scientist can receive. Credit: Dan Addison | Virginia University of Communications
Plans for Bacteria’s ‘Super Coils’
Different bacteria have one or more appendages known as flagella or plural flagella. A flagellum consists of thousands of subunits that are all the same. You would think such a tail would be straight, or at least somewhat flexible, but that would keep the bacteria from moving. This is because such shapes cannot generate thrust. It takes a spinning, corkscrew-like propeller to propel a bacterium forward. Scientists call the development of this shape a “super spiral,” and after more than 50 years of research, they now know how bacteria do it.
Egelman and colleagues discovered that the protein that makes up the flagella can be found in 11 different states using cryo-EM. The corkscrew shape is created by the exact combination of these states.
The propeller in bacteria is known to be quite different from similar propellers used by satiating 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.
