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Scientists finally cracked how bacteria's spinning motor actually works [1]

['Ellsworth Toohey']

Date: 2026-04-28  

Mike Manson has spent 50 years at Texas A&M studying the bacterial flagellar motor — a molecular machine that spins hundreds of times per second, outpacing a race car's spinning crankshaft, to drive bacteria through water. He finally understands it. "My lifelong quest is now fulfilled," he told Quanta Magazine. "I finally understand how this thing I've been studying for 50 years actually works."

The mechanism hinges on an idea that Peter Mitchell published in 1961 and spent years defending against ridicule. He called it the proton motive force: outside a bacterial cell, tens of thousands of free protons float in the surrounding fluid; inside, fewer than 100. That gradient is potential energy — like water backed up behind a dam — and protons push inward through any opening available.

The flagellar motor is that opening. Cryo-EM (cryogenic electron microscopy) studies since 2020 have finally cracked the structure. Small pentagonal-ring structures called stators sit at the motor's base. As protons flood through each one — more than 2,000 per second — they pedal the stator rings, which rub against the C ring (34 proteins at the flagellum's base), and that turning C ring spins the flagellum. Mitchell got the Nobel Prize in 1978, vindicated.

The motor can also reverse. When a bacterium senses worsening conditions — fewer nutrients in its path — phosphorylated molecules called CheY bind to the C-ring proteins and snap the whole ring into a different configuration, flipping the flagellum into reverse and causing the bacterium to tumble to reorient. "Biology can build wheels," Harvard biophysicist Aravinthan Samuel told Quanta. "Now we know."

Creationists had long held up the flagellar motor as their prime example of "irreducible complexity" — a system too intricate to have evolved step by step. Manson sees it differently. "If you understand the proton motive force," he said, "you basically understand the underpinnings of all that happens in biology."

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