Changing Gears

Changing Gears

The intricate design present in biological systems never ceases to amaze. A few months ago I wrote about molecular motors present in biological cells and how they are giving insight to researchers in nanotechnology, either providing them with improved motor designs or actual devices to use in driving man-made miniature machines. In addition, Fuz Rana’s recently released book, The Cell’s Design, is filled with examples of similar biochemical design taken from all areas of cell function.

Scientists have known for some time about the design of the flagellum, the tiny corkscrew-like propeller and motor that some bacteria use for locomotion. With a stator, rotor, shaft, bushings, and a universal joint, this microscopic motor looks a lot like those that engineers design for running our home appliances, such as refrigerators and vacuum cleaners.

Recently, researchers discovered that the flagellum motor in the bacterium Bacillus subtilis also has a clutch that allows the rotor to disengage. Reporting in the latest issue of Science (see a press release here), a research team from Indiana University Bloomington and Harvard University led by biologist Daniel Kearns learned of this capability by accident. Kearns and colleagues were actually interested in how B. subtilis ceased its wandering activity when it took up residence in stationary assemblages called biofilms. The stability of a biofilm can be jeopardized if the flagella continued to spin. Understanding biofilm formation may prove useful in combating infections.

When the scientists realized that a particular protein, EpsE, was involved in repressing the flagellar motion, they proposed two possible explanations. One was that the EpsE acted as a brake, locking up the moving and nonmoving parts; the other was that EpsE worked like a clutch, disengaging the parts from each other. They were able to devise an experiment where the tail end of the flagellum was attached to a glass slide. They observed what happened in the presence and absence of EpsE. Since the cells stopped but could still rotate passively in the presence of EpsE, they concluded that it functioned as a clutch.

“We think it’s pretty cool that evolving bacteria and human engineers arrived at a similar solution to the same problem,” said Kearns. “How do you temporarily stop a motor once it gets going?”

Their press release concluded: “The discovery may give nanotechnologists ideas about how to regulate tiny engines of their own creation. The flagellum is one of nature’s smallest and most powerful motors—ones like those produced by B. subtilis can rotate more than 200 times per second, driven by 1,400 piconewton-nanometers of torque. That’s quite a bit of (miniature) horsepower for a machine whose width stretches only a few dozen nanometers.”

While these scientists attribute this remarkable capability to an evolutionary process, in light of the superior design in evidence, it seems far more likely that it reveals the hand of a Master Designer.