Wheels of life Morgan Beeby/Imperial College London

Behold – the only known example of a biological wheel. Loved by creationists, who falsely think they are examples of “intelligent design”, the bacterial flagellum is a long tail that is spun like a propeller by nano-sized protein motors.

Now these wheels and their gearing have been imaged in high resolution and three dimensions for the first time. Morgan Beeby and his colleagues at Imperial College London used an electron microscope to resolve the mechanisms that provide different amounts of torque to the motors.

The motors are diverse, coming in a wide variety of shapes, sizes and power outputs. Indeed, the diversity of the motors and the fact that they have evolved many times in different bacterial lineages, scuppers the creationist view that the machinery is “irreducibly complex”.


Morgan Beeby/Imperial College London

The motor of Campylobacter, for example, is powerful enough to drive the bug through the protective lining of your gut wall. If that happens, you might get food poisoning. Torque is powered by a wheel-like structure on the base of the flagellum called a stator, and nano-robocists want to use the bacterial motors to avoid having to build their own.

It turns out that Campylobacter has almost twice as many stators as Salmonella, and that their stators sit in a wider ring, giving increased torque and leverage.

Beeby’s team used electron cryotomography, a method that freezes the bacteria, to allow the motor to be imaged from all angles.

Journal reference: PNAS: 10.1073/pnas.1518952113