Molecular model of a bacterial flagellar motor reveals a "parts-list" of protein adaptations to increase torque.

One hurdle to understanding how molecular machines work, and how they evolve, is our inability to see their structures . Here we describe a minicell system that enables cryogenic electron microscopy imaging and single particle analysis to investigate the structure of an iconic molecular machine, the bacterial flagellar motor, which spins a helical propeller for propulsion. We determine the structure of the high-torque motor including the subnanometre-resolution structure of the periplasmic scaffold, an adaptation essential to high torque.

Evolution of a large periplasmic disk in Campylobacterota flagella enables both efficient motility and autoagglutination.

The flagellar motors of Campylobacter jejuni (C. jejuni) and related Campylobacterota (previously epsilonproteobacteria) feature 100-nm-wide periplasmic "basal disks" that have been implicated in scaffolding a wider ring of additional motor proteins to increase torque, but the size of these disks is excessive for a role solely in scaffolding motor proteins. Here, we show that the basal disk is a flange that braces the flagellar motor during disentanglement of its flagellar filament from interactions with the cell body and other filaments.

Viscosity-dependent determinants of impacting the velocity of flagellar motility.

Bacteria can adapt flagellar motor output in response to the load that the extracellular milieu imparts on the flagellar filament to enable propulsion. Bacteria can adapt flagellar motor output in response to the load that the extracellular milieu imparts on the flagellar filament to enable propulsion through diverse environments. These changes may involve increasing power and torque in high-viscosity environments or reducing power and flagellar rotation upon contact with a surface.

Diversification of Campylobacter jejuni Flagellar C-Ring Composition Impacts Its Structure and Function in Motility, Flagellar Assembly, and Cellular Processes.

Bacterial flagella are reversible rotary motors that rotate external filaments for bacterial propulsion. Some flagellar motors have diversified by recruiting additional components that influence torque and rotation, but little is known about the possible diversification and evolution of core motor components. The mechanistic core of flagella is the cytoplasmic C ring, which functions as a rotor, directional switch, and assembly platform for the flagellar type III secretion system (fT3SS) ATPase.