September 1, 2006 | David F. Coppedge

Another Flagellum Excites Scientists

“The bacterial flagellar motor excites considerable interest because of the ordered expression of its genes, its regulated self-assembly, the complex interactions of its many proteins, and its startling mechanical abilities,” begins a paper in Nature by three Caltech scientists.1  They performed electron cryotomography imaging on the flagella of Triponema primita, a different critter with a different model from the flagellum found in E. coli, the favorite toy of microbiologists (with an outboard motor that is an icon of the intelligent design movement).  Treponema is a little spirochete that lives in the hindgut of termites.  It has two flagella, one at each end, that apparently rotate on its inside and make the organism gyrate rather than swim through liquid.
    The Caltech team got good images of the stator for the first time.  Their exterior and cross-section illustrations show a multi-part circular structure with 16-fold symmetry and complex contours, with rings and other parts of unknown function.  This particular motor apparently operates in low gear.  It is larger than the E. coli or Salmonella flagella and apparently runs at much higher torque. 

These differences have important implications for current models of the functional and architectural relationships of the components.  Whereas the Salmonella motor spins just the flagellum, because Treponema flagella are periplasmic, it is thought that they cause the whole cell to gyrate.  Thus, each rotation may be much slower and require greater torque.  The unusually large stud ring, C ring and rotor in Treponema may serve to increase torque by increasing the length of the effective lever arm through which each stator stud acts.  These larger rings may also accommodate more stator studs and FliG molecules around the ring, in effect ‘gearing down’ the Treponema motor so that the passage of each proton across the membrane produces a smaller angular rotation.

The paper includes a link to an animation video that shows the motor in operation from different angles.  The authors talk a lot about machine specs, but don’t mention anything about evolution.


1Murphy, Leadbetter and Jensen, “In situ structure of the complete Treponema primitia flagellar motor,” Nature 442, 1062-1064(31 August 2006) | doi:10.1038/nature05015.

Who would have ever thought that some tiny little bug living inside another bug would possess some of the most elaborate nanotechnology in the world.  Early microscopists like Leeuwenhoek were astonished at the motions of microscopic animalcules, but the true wonder at what makes them move is still just now coming to light.
    We hate to keep beating the Darwiniacs over the head with this high-tech motorized wet noodle, but it’s kind of fun in a perverse way.  Besides, incorrigibility deserves flagellation.

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