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

Flagella are thin, thread-like appendages extending from the plasma membrane and cell wall that help bacteria in motility.The flagellum has three main parts &#8212; the filament, the hook, and the basal body.The filament, the visible part of the flagellum, is composed of flagellin protein subunits arranged in helical chains.It is connected to its basal body by the hook.The basal body consists of a central rod passing through a series of protein rings.Gram-negative bacteria have four basal body rings. The L ring is anchored to the lipopolysaccharide layer, the P ring is embedded in the peptidoglycan layer, and the MS and C rings are attached to the plasma membrane and cytoplasm, respectively.The basal body of the Gram-positive bacteria contains only the MS and C rings.The basal body functions as a motor powered by the proton motive force, allowing the flagellum to rotate and enabling bacteria to propel themselves.Besides motility, flagella help bacteria attach to surfaces and, in some bacteria, contribute to virulence by aiding in infection.

flagella and motility in bacteria

Flagella are specialized, thread-like structures that extend from a bacteria's cell envelope. They play a crucial role in motility and chemotaxis. Their structural organization and functioning exemplify sophisticated biological engineering, enabling bacterial survival and adaptability in diverse environments.Structure of the FlagellumA bacterial flagellum consists of three key components: the filament, the hook, and basal body. The filament, a long, helical structure composed of repeating subunits of the protein flagellin and hollow at its core, acts as the primary propulsive element. The hook connects the filament to the basal body, serving as a flexible coupling that translates the motor's torque to filament rotation.The basal body forms the anchor of the flagellum within the bacterial cell envelope and is structurally diverse between Gram-negative and Gram-positive bacteria. In Gram-negative bacteria, the basal body comprises four rings: the L ring (anchored in the outer lipopolysaccharide layer), the P ring (embedded in the peptidoglycan layer), and the MS and C rings (located within the plasma membrane and cytoplasm, respectively). By contrast, Gram-positive bacteria, with their thicker peptidoglycan layer and lack of an outer membrane, possess only the MS and C rings. A central rod connects these rings, forming the core of the motor apparatus.Mechanism of Rotation and MotilityThe basal body serves as a rotary motor driven by the proton motive force (PMF). The PMF is generated by translocating protons across the bacterial membrane, creating an electrochemical gradient. As protons flow back into the cell through the motor proteins associated with the basal body, the energy released drives the rotation of the flagellum. This rotation, often reaching several hundred revolutions per second, propels the bacterium through liquid environments.Role in ChemotaxisFlagella facilitate bacterial chemotaxis, a process that allows cells to navigate toward favorable environments or escape harmful conditions. This is achieved through temporal sensing of chemical gradients, with the bacterium adjusting the direction and frequency of flagellar rotation. A counterclockwise rotation results in a smooth, directed movement known as a "run," while a clockwise rotation induces a "tumble," reorienting the cell.Flagellar motility and chemotaxis are vital for bacterial survival, enabling access to nutrients, colonization of host environments, and evasion of adverse conditions. This adaptability underscores the evolutionary significance of flagella in microbial life.

Flagella are specialized, thread-like structures that extend from a bacteria's cell envelope. They play a crucial role in motility and chemotaxis. Their ...

Education

JoVE Core

Microbiology

Unit

Microbial Cell Structure and Function        

KEY TERMS AND CONCEPTS

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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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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cell inclusions

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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.

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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