Name: bacterial flagella as tiny rotary motors
Uploaded: 2025-06-12T09:30:47.000Z
Duration: 1 min 18 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Biology

BIO.4

BIO.4.c

Flagella and Motility in Bacteria

Les flagelles sont de minces appendices filiformes filiformes qui s’étendent de la membrane plasmique et de la paroi cellulaire qui aident les bactéries à se motiliser. Le flagelle se compose de trois parties principales : le filament, le crochet et le corps basal. Le filament, partie visible du flagelle, est composé de sous-unités protéiques de la flagelle disposées en chaînes hélicoïdales. Il est relié à son corps basal par le crochet. Le corps basal est constitué d’une tige centrale passant à travers une série d’anneaux protéiques. Les bactéries à Gram négatif ont quatre anneaux basaux du corps. L’anneau L est ancré à la couche de lipopolysaccharide, l’anneau P est intégré dans la couche de peptidoglycane et les anneaux MS et C sont attachés à la membrane plasmique et au cytoplasme, respectivement. Le corps basal des bactéries à Gram positif ne contient que les anneaux MS et C. Le corps basal fonctionne comme un moteur alimenté par la force motrice du proton, ce qui permet au flagelle de tourner et aux bactéries de se propulser. Outre la motilité, les flagelles aident les bactéries à se fixer aux surfaces et, chez certaines bactéries, contribuent à la virulence en aidant à l’infection.

flagelles et motilité chez les bactéries

Les flagelles sont des structures sp&#233;cialis&#233;es, filiformes, qui s&#8217;&#233;tendent &#224; partir de l&#8217;enveloppe cellulaire bact&#233;rienne. Ils jouent un r&#244;le crucial dans la motilit&#233; et la chimiotaxie. Leur organisation structurale et leur fonctionnement illustrent une ing&#233;nierie biologique sophistiqu&#233;e, permettant aux bact&#233;ries de survivre et de s&#8217;adapter &#224; des environnements vari&#233;s.
Structure du flagelle
Un flagelle bact&#233;rien se compose de trois &#233;l&#233;ments principaux : le filament, le crochet et le corps basal. Le filament, structure h&#233;lico&#239;dale allong&#233;e constitu&#233;e de sous-unit&#233;s r&#233;p&#233;t&#233;es de la prot&#233;ine flagelline et creux en son centre, agit comme l&#8217;&#233;l&#233;ment propulseur principal. Le crochet relie le filament au corps basal et sert de couplage flexible transmettant le couple moteur &#224; la rotation du filament.
Le corps basal constitue l&#8217;ancrage du flagelle dans l&#8217;enveloppe cellulaire bact&#233;rienne et pr&#233;sente une structure diff&#233;rente selon que la bact&#233;rie est &#224; Gram n&#233;gatif ou &#224; Gram positif. Chez les bact&#233;ries &#224; Gram n&#233;gatif, le corps basal comprend quatre anneaux : l&#8217;anneau L (ancr&#233; dans la couche externe de lipopolysaccharides), l&#8217;anneau P (situ&#233; dans la couche de peptidoglycane), et les anneaux MS et C (respectivement localis&#233;s dans la membrane plasmique et le cytoplasme). En revanche, les bact&#233;ries &#224; Gram positif, dont la couche de peptidoglycane est plus &#233;paisse et d&#233;pourvue de membrane externe, ne poss&#232;dent que les anneaux MS et C. Une tige centrale connecte ces anneaux, formant le noyau de l&#8217;appareil moteur.
M&#233;canisme de rotation et motilit&#233;
Le corps basal fonctionne comme un moteur rotatif aliment&#233; par la force proton-motrice (PMF). La PMF est g&#233;n&#233;r&#233;e par le transfert de protons &#224; travers la membrane bact&#233;rienne, cr&#233;ant un gradient &#233;lectrochimique. Lorsque les protons retournent dans la cellule via les prot&#233;ines motrices associ&#233;es au corps basal, l&#8217;&#233;nergie lib&#233;r&#233;e entra&#238;ne la rotation du flagelle. Cette rotation, pouvant atteindre plusieurs centaines de tours par seconde, propulse la bact&#233;rie dans les milieux liquides.
R&#244;le dans la chimiotaxie
Les flagelles permettent la chimiotaxie bact&#233;rienne, un processus par lequel les cellules se dirigent vers des environnements favorables ou fuient des conditions d&#233;favorables. Cela est rendu possible par la d&#233;tection temporelle de gradients chimiques, la bact&#233;rie ajustant la direction et la fr&#233;quence de rotation des flagelles. Une rotation antihoraire provoque un mouvement fluide et orient&#233;, appel&#233; &#171; run &#187;, tandis qu&#8217;une rotation horaire induit une &#171; tumble &#187;, r&#233;orientant la cellule.
La motilit&#233; flagellaire et la chimiotaxie sont essentielles &#224; la survie bact&#233;rienne, permettant l&#8217;acc&#232;s aux nutriments, la colonisation des environnements h&#244;tes et l&#8217;&#233;vitement des conditions n&#233;fastes. Cette capacit&#233; d&#8217;adaptation souligne l&#8217;importance &#233;volutive des flagelles dans la vie microbienne.

Flagelles et motilité chez les bactéries

Les flagelles sont des structures sp&#233;cialis&#233;es, filiformes, qui s&#8217;&#233;tendent &#224; partir de l&#8217;enveloppe cellulaire ...

Education

Enseignement

JoVE Core

Microbiology

Microbiologie

Unit

Unité

Microbial Cell Structure and Function        

Structure et fonction des cellules microbiennes

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

bacterial flagella as tiny rotary motors

Bacterial flagella are thread-like structures that help cells move and respond to their surroundings. They extend from the cell envelope and support both motility and chemotaxis, which is the ability to move in response to chemical signals. Their design shows how bacteria use specialized structures to survive in different environments.

A flagellum has three main parts: the filament, the hook, and the basal body. The filament is the long, helical part made of repeating flagellin protein subunits, and it is hollow at the center. The hook acts as a flexible connector that passes torque from the motor to the filament.

The basal body anchors the flagellum inside the bacterial cell envelope. Its structure differs between Gram-negative and Gram-positive bacteria. Gram-negative bacteria have four rings: the L ring in the outer lipopolysaccharide layer, the P ring in the peptidoglycan layer, and the MS and C rings in the plasma membrane and cytoplasm. Gram-positive bacteria have a thicker peptidoglycan layer and no outer membrane, so they have only the MS and C rings. A central rod connects the rings and forms the core of the motor.

The basal body works as a rotary motor powered by the proton motive force, or PMF. PMF is an electrochemical gradient made by moving protons across the bacterial membrane. When protons flow back through motor proteins linked to the basal body, the released energy drives flagellar rotation. This rotation can reach several hundred revolutions per second and pushes the bacterium through liquid.

Flagella also help bacteria perform chemotaxis. Cells sense chemical gradients over time and change how often and in which direction the flagellum rotates. Counterclockwise rotation produces a smooth run, while clockwise rotation causes a tumble that reorients the cell. This movement helps bacteria reach nutrients, colonize host environments, and avoid harmful conditions.

Bacterial Flagella as Tiny Rotary Motors

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archaeal cell wall

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flagella and motility in bacteria

Bacterial flagella are thread-like structures that help cells move and respond to their surroundings. They extend from the cell envelope and support both motility and chemotaxis, which is the ability to move in response to chemical signals. Their design shows how bacteria use specialized structures to survive in different environments. A flagellum has three main parts: the filament, the hook, and the basal body. The filament is the long, helical part made of repeating flagellin protein...

fimbriae, pili, and axial filaments

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nucleoid

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surface appendages of archaea

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key terms and concepts

Learn how bacterial flagella work as rotary motors, how Gram-negative and Gram-positive cells differ, and how runs and tumbles guide chemotaxis.

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BIO.4.e

Bacterial Flagella as Tiny Rotary Motors

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