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

I flagelli sono appendici sottili e filiformi che si estendono dalla membrana plasmatica e dalla parete cellulare e aiutano i batteri nella motilità. Il flagello ha tre parti principali: il filamento, l'uncino e il corpo basale. Il filamento, la parte visibile del flagello, è composto da subunità proteiche flagelliniche disposte in catene elicoidali. È collegato al suo corpo basale tramite l'uncino. Il corpo basale è costituito da un'asta centrale che passa attraverso una serie di anelli proteici. I batteri Gram-negativi hanno quattro anelli basali del corpo. L'anello L è ancorato allo strato di lipopolisaccaridi, l'anello P è incorporato nello strato di peptidoglicano e gli anelli MS e C sono attaccati rispettivamente alla membrana plasmatica e al citoplasma. Il corpo basale dei batteri Gram-positivi contiene solo gli anelli MS e C. Il corpo basale funziona come un motore alimentato dalla forza motrice del protone, consentendo al flagello di ruotare e ai batteri di spingersi. Oltre alla motilità, i flagelli aiutano i batteri ad attaccarsi alle superfici e, in alcuni batteri, contribuiscono alla virulenza favorendo l'infezione.

flagelli e motilità nei batteri

I flagelli sono delle strutture specializzate, filiformi, che si estendono dall&#8217;involucro cellulare dei batteri. Essi svolgono un ruolo cruciale nella motilit&#224; e nella chemiotassi. La loro organizzazione strutturale e il loro funzionamento rappresentano un esempio sofisticato di ingegneria biologica, che consente la sopravvivenza e l&#8217;adattabilit&#224; batterica in ambienti diversi.
Struttura del flagella
Un flagello batterico &#232; composto da tre componenti principali: il filamento, il gancio e il corpo basale. Il filamento, una lunga struttura elicoidale costituita da subunit&#224; ripetute della proteina flagellina e cava al centro, funge da elemento propulsivo primario. Il gancio collega il filamento al corpo basale, servendo da giunto flessibile che trasmette la coppia motrice del motore alla rotazione del filamento. Il corpo basale costituisce l&#8217;ancoraggio del flagello all&#8217;interno dell&#8217;involucro cellulare batterico ed &#232; strutturalmente diverso nei batteri Gram-negativi e Gram-positivi. Nei batteri Gram-negativi, il corpo basale comprende quattro anelli: l&#8217;anello L (ancorato nello strato di lipopolisaccaridi esterno), l&#8217;anello P (incorporato nello strato di peptidoglicano), e gli anelli MS e C (localizzati rispettivamente nella membrana plasmatica e nel citoplasma). Al contrario, i batteri Gram-positivi, dotati di uno spesso strato di peptidoglicano e privi di membrana esterna, possiedono solo gli anelli MS e C. Una barra centrale collega questi anelli, costituendo il nucleo dell&#8217;apparato motore.
Meccanismo di rotazione e motilit&#224;
Il corpo basale funge da motore rotativo alimentato dalla forza proton-motrice (PMF). La PMF &#232; generata dal trasporto di protoni attraverso la membrana batterica, creando un gradiente elettrochimico. Quando i protoni rientrano nella cellula attraverso le proteine motrici associate al corpo basale, l&#8217;energia rilasciata guida la rotazione del flagello. Questa rotazione, che pu&#242; raggiungere diverse centinaia di giri al secondo, consente al batterio di muoversi in ambienti liquidi.
Ruolo nella chemiotassi
I flagelli facilitano la chemiotassi batterica, un processo che permette alle cellule di dirigersi verso ambienti favorevoli o di allontanarsi da condizioni nocive. Questo avviene attraverso la percezione temporale dei gradienti chimici, con il batterio che regola la direzione e la frequenza della rotazione flagellare. Una rotazione in senso antiorario produce un movimento rettilineo e continuo detto &#8220;corsa&#8221;, mentre una rotazione in senso orario induce una &#8220;rotazione casuale&#8221;, che riorienta la cellula.
La motilit&#224; flagellare e la chemiotassi sono vitali per la sopravvivenza batterica, poich&#233; permettono l&#8217;accesso ai nutrienti, la colonizzazione di ambienti ospiti e l&#8217;elusione di condizioni avverse. Questa capacit&#224; di adattamento evidenzia l&#8217;importanza evolutiva dei flagelli nella vita microbica.

Flagelli e motilità nei batteri

I flagelli sono delle strutture specializzate, filiformi, che si estendono dall&#8217;involucro cellulare dei batteri. Essi svolgono un ruolo cruciale ...

Education

Didattica

JoVE Core

Microbiology

Microbiologia

Unit

Unità

Microbial Cell Structure and Function        

Struttura e funzione della cellula microbica

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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

prokaryotic vs. eukaryotic cells

Cell Organization in Prokaryotes and Eukaryotes

Prokaryotic and eukaryotic cells show two major patterns of cell organization. These differences shape the structure, size, and function of living things across the domains of life. Prokaryotic cells, such as bacteria and archaea, are simple in structure. They do not have a nucleus or other membrane-bound organelles. Their DNA is usually a single circular molecule found in the nucleoid region, which is not surrounded by a nuclear membrane. Prokaryotes are usually very small, about 0.1 to 5.0...

microbial morphologies 

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Microbial shapes and cell forms help bacteria, archaea, and eukaryotic microbes survive in many environments. Cell shape affects how these organisms grow, take up nutrients, and handle waste. It also reflects the link between structure and function. Among bacteria, cocci and bacilli are the most common shapes. Cocci are spherical cells, and they may appear alone or in pairs called diplococci, chains called streptococci, clusters called staphylococci, or groups of four called tetrads. Bacilli...

bacterial cell wall 

Gram-Positive and Gram-Negative Walls

Bacterial cell walls give bacteria their shape and help protect them from osmotic stress. This rigid but flexible layer surrounds the plasma membrane and supports cellular integrity. Its main building block is peptidoglycan, a mesh-like polymer that adds strength while still allowing some flexibility. Peptidoglycan is made of alternating N-acetylglucosamine, or NAG, and N-acetylmuramic acid, or NAM. Short amino acid chains connect these sugar units and help form the strong network. The...

archaeal cell wall

Archaeal Cell Wall Types and Functions

Archaeal cell walls protect archaea and help them survive in extreme environments. Unlike bacterial cell walls, they do not have the peptidoglycan layer found in most bacteria. Instead, archaea use a range of materials, including proteins, polysaccharides, and pseudomurein, to build their outer layer. The most common archaeal cell wall is the S-layer, or surface layer. It is made of tightly packed protein or glycoprotein units that form a crystalline lattice. These repeating patterns can make...

peptidoglycan synthesis

Building the Bacterial Cell Wall

Peptidoglycan builds the bacterial cell wall and gives the cell its shape and strength. It is a mesh-like polymer around the bacterial plasma membrane. The polymer is made of repeating sugar units, N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), linked by β-1,4 glycosidic bonds. Short peptide chains cross-link the sugar chains and make the wall more rigid. Peptidoglycan biosynthesis starts in the cytoplasm with soluble precursors. Uridine diphosphate, or UDP, binds to NAG and NAM to...

plasma membrane in bacteria and archaea

Bacterial vs Archaeal Membrane Lipids

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outer layers of the cell envelope

Capsules, Slime Layers, and S-Layers

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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

How Bacteria Stick, Share Genes, and Move

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cell inclusions

Prokaryotic Cell Storage Inclusions

Prokaryotic cell storage inclusions help bacteria store nutrients, manage energy, and adapt to changing environments. These inclusions let cells survive when food, phosphate, sulfur, light, or oxygen levels change. They are important examples of how simple cells can still have highly specialized structures. Some inclusions store carbon. Poly-β-hydroxybutyric acid, or PHB, forms granules that act as a long-term carbon and energy reserve. Glycogen granules also store carbon, but they provide a...

endospores and sporulation

How Bacteria Survive with Endospores

Endospores help some bacteria survive harsh conditions. These dormant cells are made mainly by Gram-positive bacteria such as Bacillus and Clostridium. They are highly resistant to heat, ultraviolet and ionizing radiation, drying, and toxic chemicals. In rare cases, endospore-like structures have also been seen in some Gram-negative bacteria, including Coxiella burnetii and Sporosarcina ureae, as well as in other species exposed to extreme conditions. Sporulation begins when bacteria face...

nucleoid

How Prokaryotes Organize DNA

Prokaryotes organize their DNA in the nucleoid, a distinct region where genetic material and associated proteins are packed. Because prokaryotic cells do not have a membrane-bound nucleus, the nucleoid helps keep DNA organized and available for cell activities. In most bacteria and archaea, the DNA is a single, circular, double-stranded molecule that is tightly compacted by supercoiling and protein interactions. Nucleoid-associated proteins, or NAPs, help shape and maintain this DNA region.

surface appendages of archaea

Archaeal Pili and Archaella in Action

Archaeal pili and archaella help archaea survive, attach, and move in challenging environments. These surface appendages support adhesion, biofilm formation, and motility. They give archaeal cells key advantages in habitats that can be extreme. Pili are filament-like structures made from pilin protein subunits. Their main role is adhesion, which means helping cells stick to surfaces. They also support biofilm formation, where cells live in a shared, surface-attached community. Some pili are...

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.

Bacterial Flagella as Tiny Rotary Motors | JoVE K12

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BIO.4.e

Bacterial Flagella as Tiny Rotary Motors

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