Molecular Mechanism for Bacterial Sliding

[BillTre]

TL;DR

A molecular mechanism by which a bacteria can slide along a substrate has been described.

This article from Science Advances (probably not open access, an AAAS publication) has described a complex and interesting molecular mechanism (a nano-bio-molecular machine).
A rotary motor in the cell membrane (driving mechanisms unknown) spins a gear that pushes a "tread" along a track imbeded between the cell's inner and outer membranes in a peptidoglycan layer. The tread poke through the outer membrane topped off with an adhesin molecule which binds things in the substrate. Adhesin molecules are proteins that bind particular extracellular molecules, underlying cell to cell adhesion. This gives the mechanism resistance to move forward with. Since the track spirls around the cell, the cell rotates on its long axis as it moves forward along its access.

Picture of their hypothesized mechanism:
https://www.physicsforums.com/attachments/258274

Here is their cartoon movie (click on movie S5) of how it works can be found here (may not be behind paywall since it is supplemental material).

I find these evolved complex molecular machines that cells make use of to be fascinating.

 

[berkeman]

Pretty amazing. Thanks Bill.

From the S5 movie:

 

[BillTre]

Thanks for posting that @berkeman.
Not sure what happened to the figure that was in my post, but the video pictures show most of it.
I'll try adding it back.

 

[256bits]

So what is the point of bacterial mobility?
They would be using energy for some purpose.
Do they sense a gradient of some sort ( chemical, photo, electrical )?
At on um per second they don't get to far quickly.

 

[BillTre]

I think that bacteria can go towards or away from increasing concentrations of chemicals (either foods or bad stuff) and can go toward or away from light or up or down in a gravitational field and follow magnetic field lines.
Any of these, appropriately used, can be beneficial to the organism, and would thereore be expected to be selected for.
In the long run, the energy expenditure should normally be expected provide greater energy benefits than its costs.
However, a prevention of death would over-rule that.