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Flagellum gives bacteria a sense of touch. Behe is right.

bacteria sense surfaces with flagellum/U Basel, Biozentrum

Irreducible complexity. From ScienceDaily:

Although bacteria have no sensory organs in the classical sense, they are still masters in perceiving their environment.

Swimming Caulobacter bacteria have a rotating motor in their cell envelope with a long protrusion, the flagellum. The rotation of the flagellum enables the bacteria to move in liquids. Much to the surprise of the researchers, the rotor is also used as a mechano-sensing organ. Motor rotation is powered by proton flow into the cell via ion channels. When swimming cells touch surfaces, the motor is disturbed and the proton flux interrupted.

The researchers assume that this is the signal that sparks off the response: The bacterial cell now boosts the synthesis of a second messenger, which in turn stimulates the production of an adhesin that firmly anchors the bacteria on the surface within a few seconds. “This is an impressive example of how rapidly and specifically bacteria can change their behavior when they encounter surfaces,” says Jenal. Paper. (paywall) – Isabelle Hug, Siddharth Deshpande, Kathrin S. Sprecher, Thomas Pfohl, Urs Jenal. Second messenger–mediated tactile response by a bacterial rotary motor. Science, 2017; 358 (6362): 531 DOI: 10.1126/science.aan5353 More.

From the paper:

Elucidating a bacterial sense of touch

Bacteria can adhere to surfaces within the host. This leads to tissue colonization, induction of virulence, and eventually the formation of biofilms—multicellular bacterial communities that resist antibiotics and clearance by the immune system (see the Perspective by Hughes and Berg). Hug et al. show that bacteria have a sense of touch that allows them to change their behavior rapidly when encountering surfaces. This tactile sensing makes use of the inner components of the flagellum, a rotary motor powered by proton motif force that facilitates swimming toward surfaces. Thus, the multifunctional flagellar motor is a mechanosensitive device that promotes surface adaptation. In complementary work, Ellison et al. elucidate the role of bacterial pili in a similar surface-sensing role.

From the Abstract:

When bacteria encounter surfaces, they respond with surface colonization and virulence induction. The mechanisms of bacterial mechanosensation and downstream signaling remain poorly understood. Here, we describe a tactile sensing cascade in Caulobacter crescentus in which the flagellar motor acts as sensor. … Thus, the bacterial flagellar motor acts as a tetherless sensor reminiscent of mechanosensitive channels.


Nature prefers using electrostatic force, and human inventors have typically used electromagnetic force. This is also true of radio, where fish use the static side of waves while human radio transmitters use the magnetic side. There are only a few patents for electrostatic motors. Most of them re-invented the bacterial structure, even though the cilia motor hadn't been seen yet. (eg patent 2,232,143 from 1938.) As far as I can tell, none of them re-invented the use of the motor as a sensor. Feedback and stop detection aren't mentioned in the patents. The bacterial circuit described in this paper could be mimicked nicely by placing a relay coil in parallel with the motor, and powering the pair with a regulated current source. When the motor stops turning, it stops consuming current, so the regulated current would pass instead through the relay coil, which would then trigger the adhesion mechanism. Can't get ahead of Nature no matter how hard we try. polistra
"Much to the surprise" - always with the 'astonish', 'surprise', 'amaze'. When it comes to research, they never find what they are expecting or hoping for. Are these words required for budget considerations? I suppose if they had written "and just as we thought...", the science would be settled and the trickle of grants would dry. It is sad really. Belfast

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