Crack the 50-year puzzle! Why do bacteria move? New Cell study reveals key structures

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by WuXi AppTec Content Team Since Leeuwenhoek observed rapidly swimming bacteria under the microscope, scientists have been eager to uncover the secrets
of bacterial movement.
But it wasn't until today, more than 300 years later, that the answer has gradually surfaced
.

We have long known from textbooks that bacteria rely on flagella for movement
.
Indeed, flagella are the motor organs peculiar to most bacteria, and they consist of three parts: a motor on the bacterial membrane, an extracellular joint device, and
a flagellar filament.
The mechanism by which flagellates make bacteria move involves two key questions: how does the flagellar motor provide power, and how does the flagellar filament, which acts as a "propeller", transform into a form suitable for movement?
Image source: 123RF
For the first question, last year's Cell paper described an important advance
.
Professor Zhu Yongqun and Professor Zhang Xing of Zhejiang University collaborated to resolve the structure of the bacterial flagellar motor at atomic resolution, and how to assemble and power the operation of the flagellum
wire efficiently.
(Read more: Milestones!) Explain in detail how one of the most sophisticated molecular motors in nature works, published by the Zhejiang University research team "Cell")
As for the second problem, scientists have been arguing about the suspense for
half a century.
What is known is that by curling the slender flagellar into a spiral, bacteria can obtain temporary "thrusters", like the propellers of a helicopter, by rotating to generate power and push themselves to move
quickly.

But how is this deformation process achieved? In a recent study published in the journal Cell, Professor Edward H.
Egelman of the University of Virginia led the team to unravel the mystery
.
With the help of cryo-electron microscopy and computer simulation, the research team cracked the mechanism of diflagellar filament formation in near-atomic resolution, and revealed the convergence evolution
of bacteria and archaeal flagellar filaments.


"As early as 50 years ago, models began to describe how these flagellar filaments form such a regular spiral, and now we have revealed the details of the structure of the flagellar filaments," Professor Egelman said, "Our research shows that those models are wrong, and the new understanding we bring will facilitate the development of new technologies
based on these miniature 'thrusters'.
" "
Each filament of the bacterium is made up
of thousands of identical subunits.
We might think that the flagellar should be nearly straight, or just a little elastic
.
But in fact, such a structure simply cannot produce enough thrust, so the bacteria will have difficulty moving
.
Only by winding into a spiral can the bacteria move
.
Scientists call this process supercoil
.

Under cryo-EM, the research team looked at the core domains
of the flagellum.
In the lowest energy state, the protofilament that makes up the flagellum filament has 11 different conformations, as shown in the figure below, and these protofilaments are arranged in a circular pattern along the longitudinal axis, forming a cylindrical shape
.
Due to their different conformations, they vary in length, and the originally straight cylinders curve to the side of the shorter protofilament, thus curling to form a supercoil
.

▲The process by which bacteria (top) and the flagellar filaments of archaea (bottom) form a supercoil morphology (Image: Reference[1])
In addition, this study also analyzes
the structure of archaeal flagellum.
Compared with bacteria, people's understanding of archaea is more limited
.

Under cryo-EM, there are 10 different conformations of the protofilaments that make up the archaeal flagellar filaments
.
Although there are many details of archaea and bacteria (e.
g.
, the core domain of the archaeal flagellar filament is single chain and the bacteria is multi-chain), the end result is quite consistent: the flagellar turns into a regular supercoil
.

In this case, the research team concluded, archaea and bacteria converged to evolve: nature found similar solutions
in different ways.
In other words, although bacteria and archaea have similar composition and function, the two evolved these characteristics independently
.

Through convergent evolution, bacteria and archaeal flagellar have similar superhelix structures (Image: Reference [1])
"Considering that these structures have been on Earth for billions of years, it seems that it is not so long to understand this problem in 50 years
.
Professor Egelman concluded
.
[1] Mark A.
B.
Kreutzberger et al, Convergent evolution in the supercoiling of prokaryotic flagellar filaments, Cell (2022).
DOI: 10.
1016/j.
cell.
2022.
08.
009[2] Ending a 50-year mystery, scientists reveal how bacteria can move.
Retrieved September 27, 2022 from