The Tentacle Under The Microscope
Run for the hills! Cthulhu is not just in the realm of imagination anymore. It’s right here and right now–abeit in microscopic form.
For quite some time, it’s been known that bacteria move. Most people have the idea that bacterial propulsion is mediated by the flagella and cilia which help the microbe swim and tumble. Another type of bacterial locomotion concerns “gliding motility” in which the cell secretes a slime trail–the resulting physical forces allowing the bacterium to ooze its way along like the Blob. Bacteria can also drag themselves along via grappling hooks which are formed by structures called pili. The pili act as tethers which hook onto the surface and the cell merely reels them in to pull itself into a certain direction.
Mycoplasma mobile is one of these microorganisms that supposedly have gliding motility. It was originally isolated in 1984 by Kirchhoff and Rosengarten in the gills of the Tinca tinca, a fish called the trench. It’s believed that this type of motility is associated with the infectivity of this bacterium. However, a recent paper in the Proceedings of the National Academy of Sciences by Nakane and Miyata found that what drives the movement of M. mobile is far different than slime trails and grappling hooks–in fact, the authors compare the movement to that of a jellyfish.
M. mobile movement had previously been classified as gliding, but the researchers wanted to find out exactly which mechanism was being used for it. To do this, the researchers killed the bacterium with a detergent that partially damaged the cellular membrane so that one could see into the interior of the cell but left the cytoskeleton intact. The result was a bacterial “ghost” that, amazingly, could still move when energy in the form of ATP was added to the system.
The visible inside structures of these “ghosts” were unusual–the cytoskeleton of M. mobile consisted of a jellyfish structure that contained a “bell” and associated “tentacle” structures studed with particles. The proteins that make up this jellyfish structure have no known homologue in other systems and M. mobile mutants that cannot glide have a disrupted structure. Although it’s still not known exactly how the jellyfish structure is involved in M. mobile movement, Nakane and Miyata do postulate some possible roles. Perhaps the jellyfish structure acts as a scaffold to support the gliding machinery. Or it could act as a transporter to move the gliding machinery to its proper location. Or even more wildly–act as a coordinator for bacterial “leg movements” enabling it to crawl around like a cephalopod on the sea floor.
Wriggling tentacles that act like legs? Oh come on, you might say. That’s not Cthulhu. It sounds more like a millipede. But whether it resembles a jellyfish or an insect, this is another example of the diversity of locomotion in even just bacteria–as apparently, none of them have any problem reinventing the wheel.