Flagellar motor decoded
- What happened: Scientists published new findings on how the bacterial flagellar motor works after fifty years of study. - The key specific: The report clarifies mechanical steps that enable bacterial rotation and motility. - Context/reaction: The result refines understanding of fundamental cellular machinery and could inform nano‑scale engineering efforts (x.com).
Bacteria swim by spinning a corkscrew tail, and new papers are pinning down how the tiny motor at its base actually turns. (pnas.org) In a Proceedings of the National Academy of Sciences paper accepted on October 27, 2025, Basarab G. Hosu, Alina M. Vrabioiu, and Aravinthan D. T. Samuel tested the long-debated idea that the motor’s torque-generating stator units rotate as part of the mechanism. (dmg5c1valy4me.cloudfront.net) Using polarized photobleaching microscopy in tethered *Escherichia coli*, the team reported that the MotB dimer turned at the same angular speed as the cell body, while the MotA pentamer turned 6.2 times faster than the flagellar motor. (dmg5c1valy4me.cloudfront.net) That result supports a gear-like picture: five MotA proteins arranged around two MotB proteins act as a smaller rotary unit that pushes on the larger rotor ring to drive the flagellum. (dmg5c1valy4me.cloudfront.net) The finding lands in a field shaped for more than 50 years by work on bacterial chemotaxis, the system that lets cells bias their movement toward food and away from harmful conditions. Harvard said the two 2026 PNAS studies were begun in Howard Berg’s lab and finished in Samuel’s lab after Berg’s death in 2021. (mcb.harvard.edu) A separate 2026 *Nature Physics* paper addressed a different step in the same machine: how the motor flips between clockwise and counterclockwise rotation when bacteria sense changes in their environment. Henry H. Mattingly and Yuhai Tu modeled that switch as a mechanical tug-of-war among stator-linked subunits rather than a purely equilibrium process. (nature.com) That model says the motor’s sensitivity should rise with the number of stators driving it, linking chemical sensing to the machine’s mechanical load. (nature.com) Structural work has also filled in the hardware around the motor. A 2025 *Nature Microbiology* study on *Campylobacter jejuni* mapped periplasmic disks and showed that PflA-PflB assembly recruits FliL to scaffold more stator complexes at a wider radius, increasing torque. (nature.com) Another *Nature Microbiology* paper published on January 9, 2026, described an E ring of 17 FlgY homodimers and a cage-like scaffold in *C. jejuni* that stabilized 17 torque-generating stator complexes. (nature.com) Michael D. Manson, in a February 10, 2026 PNAS commentary titled “Flagellar rotation comes full circle,” framed the new stator-rotation evidence as a milestone in explaining how ion flow is converted into motion in one of biology’s smallest rotary engines. (pnas.org)
