Shepherdless,
debunking indeed! This is how it usually goes: "Bacterial flagella
have functions and mechanisms that have differentiated during evolution."
In the same breath one then says: "However, the evolutionary history and
relationships of these functions and mechanisms remain unclear." See no. 6
above.
Cofty,
as you might have noticed, Shepherdless had a problem with my argument of
complexity. This drives the point home. And it’s not completely out of context,
seeing that it is part and parcel of various bacteria, which are included in
our discussion.
While on the subject, I see a third flagellar
motor has been discovered. Absolutely brilliant, i.e., the design of the motor and the way it was discovered. Howard Berg's latest paper in Current Biology announces an exciting find: another rotary motor has been
discovered in a bacterial cell. The Harvard expert on the bacterial
flagellum (see him speaking about the "Marvels
of Bacterial Behavior" above), along with two colleagues, describes a new
kind of rotating motor in a bacterium, separate and distinct from ATP synthase and the kind of flagella found in E. coli. The short title of the paper is dramatic:
"A Rotary Motor Drives Flavobacterium Gliding."
Cells of Flavobacterium johnsoniae, a rod-shaped bacterium devoid of pili or flagella,
glide over glass at speeds of 2-4 ?m/s. Gliding is powered by
a protonmotive force, but the machinery required
for this motion is not known. Usually, cells move along straight paths, but
sometimes they exhibit a reciprocal motion, attach near one pole and flip end
over end, or rotate. This behavior is similar to that of a Cytophaga species
described earlier.... To learn more about the gliding
motor, we sheared cells
to reduce the number and size of SprB filaments and tethered cells to glass by
adding anti-SprB antibody. Cells spun about fixed points,
mostly counterclockwise, rotating at speeds of 1 Hz or more. The torques required to sustain
such speeds were large, comparable to those generated by the flagellar rotary
motor. However, we found that a gliding motor runs at constant speed rather than at
constant torque. Now, there are three rotary
motors powered by protonmotive force: the bacterial flagellar motor, the Fo ATP
synthase, and the gliding motor.
What this implies is even more irreducible complexity for
the bacterial flagellum. Without the flagellum+T3SS working cooperatively, the
flagellum will not work, because T3SS is "required for secretion of axial
components" of the flagellum. This suggests that both the T3SS and the
flagellum had to exist simultaneously for the flagellum to assemble properly
and function.
The article concludes: "That's
a suggestion that will surely be debated between evolutionists and design
advocates. What's clear at this point is that another irreducibly complex,
functional system for motility has been revealed, based on a rotary engine
driven by proton-motive force. Harvard's announcement will certainly stimulate
further research into this gliding motor and how it works. Not surprisingly,
they feigned no hypothesis about how this system might have evolved." This is certainly music to my ears.