December 1, 2020 | David F. Coppedge

Flagellar Motor Is Actually Many Motors

A new model of the bacterial flagellum, an icon of intelligent design, has just increased the design complexity even more.

Dr Michael Behe of Lehigh University introduced the public to the wonders of the bacterial flagellum in his 1996 classic, Darwin’s Black Box. In those days of rather hazy electron micrographs of the molecular motor, scientists discerned a stator and a rotor that turned the long, threadlike flagellum (L. for whip) that enables bacteria to swim. Illustra Media made it a centerpiece of the intelligent design film, Unlocking the Mystery of Life.

Bacterial flagellum (Illustra Media), an amazing machine present in some bacteria.

In the intervening years, much has been learned. Biochemists knew that the flagellum was powered by an ion motive force (either H+ or Na+), but how the rotor and stator interacted to create rotation has been a mystery.

Now, scientists at the University of Copenhagen have perceived a new model for the rotation mechanism. The famous molecular machine doesn’t have just one rotor on the spin axis; it has multiple rotors surrounding the main rotor, making it turn.

Quite surprisingly, the team shows that the stator unit itself is in fact also a tiny rotary motor. This tiny motor powers the large motor, which makes the threads rotate, causing the bacteria to move. The results contradict existing theories on the mechanism of the stator unit, and this new knowledge might be useful in the fight against bacteria-based diseases.

These smaller motors, named MotA, turn around their own axes on components (MotB) that are anchored to the membrane. A diagram in the article shows the configuration of these subunits in beautiful detail.

“The motor consists of two proteins: MotA and MotB. The MotB protein is anchored to the cell wall, and is surrounded by MotA proteins, which, upon dispersion of the ion motive force, rotates around MotB. The rotation of MotA in turn powers rotation of the large bacteria motor,” says Nicholas Taylor.

Is there an advantage to the bacterium to have the motor configured this way?

“Furthermore, our model shows how the stator unit can power rotation of the bacterial flagellar motor in both directions, which is crucial for the bacteria to change their swimming direction. Without direction change, bacteria would only be able to swim straight in one direction.”

The article does not state how many MotA+B subunits are arranged around the stator, but the proof of the efficacy is in the performance. Some flagella can rotate at over 100,000 rpm. According to Jed Macosco in the Unlocking film, they can stop in a quarter-turn and spin at 100,000 rpm in the opposite direction. See a related article in Evolution News.

There are additional diagrams in the paper by Santiveri et al. in Cell, “Structure and Function of Stator Units of the Bacterial Flagellar Motor” (14 Sept 2020).

If this is the secret to torque generation in the flagellum, it is wondrous to behold but also more challenging for evolution. Now, instead of a single motor, there are multiple motors that have to be constructed, assembled, and arranged properly around the stator. The amount of irreducible complexity increases accordingly.

In addition, they must be coordinated so that they can all turn in unison and reverse in unison almost instantaneously. This is marvelous to see how things work at the molecular level. ID theory predicts that the closer one looks at biological design, the more designed it looks. That has been true for 24 years with this icon of design.

Speaking of Behe, he has a new book out, A Mousetrap for Darwin. It’s a large annotated collection of his responses to critics of his books about intelligent design, including from evolutionists trying to explain the bacterial flagellum with Darwinian theory.




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