Do Bacteria Have Flagella? 13 Facts You Should Know


In this article we will discuss what are flagella and do bacteria have flagella.

Flagella (singular; flagellum) are microscopic filamentous structure that originates from cytoplasm and protrude through cell wall in a whip-like appearance. They promote motility in bacteria and increase survival chances.

13 facts you should know about flagella;

  1. The word ‘flagella’ has Proto-Indo European origin; where the word ‘flagrum’ translates to “to strike” and Latin word ‘flagellum’ means “whip”.
  2. Flagella are 12-30 nm in width and 5-16 µm in length. They are usually much longer than the bacteria itself.
  3. Flagella are divided into three parts, I.e., Basal body, Hook and Filament.
  4. Basal body, is embedded into the cytoplasmic membrane by ring like structures. It works as a flagellar motor. It is made of 7 different proteins.
  5. Hook, is a connector between basal body and filament, embedded in the cell envelope and made of protein FlgE. They act as universal joint which transmit torque from one axis to the other, set at a fixed angle.
  6. Filament, is situated external to the cell and made of polymerized molecule of single protein, I.e., flagellin.
    • In eukaryotic bacteria flagellin subunits are arranged in a 9+2 fashion, I.e., nine peripheral doublet microtubules surrounding a pair of single microtubules.
  7. Flagella of bacteria share a common rotary nanomachine that generates the torque needed for filament rotation. The torque is created using protein motive force (PMF) or sodium ion motive force (NaMF) generated from ion flux through an ion channel of each transmembrane stator units.
  8. The direction of bacterial movement is determined by bacterial intracellular chemotactic signaling pathways which works in response to environmental changes like; light, temperature, pH, changes in chemicals like amino acids and sugar etc.
  9. ‘Corkscrew’ rotation of helical flagella propels the bacterium. Anticlockwise rotation of flagella results in forward movement, whereas clockwise rotation results in random ‘tumbling’ motions.
  10.  Bacteria have four ring complexes in their basal body, one in each layer.
    • C ring, embedded into cytoplasm.
    • MS ring, embedded into plasma membrane.
    • P ring, inserted into peptidoglycan layer.
    • L ring, associated with lipopolysaccharide layer.
  11.  Although flagella and cilia have fundamentally same structure; they differ in various aspects. Such as,
    • Only eukaryotic cells possess cilia, but flagellum may be present in both eukaryotic and prokaryotic cells.
    • Cilia are respectively shorter and more in number than flagella.
    • Cilia beat in a rhythmic pattern, either synchronous or metachronic; but flagella move independently from each other.
    • Cilia use ATPase activity of kinesin to generate energy needed for motion; whereas flagella use PMF.
  12.  Except locomotion, flagella also help in signal transduction and sensing surrounding environment. It acts as a virulence factor by colonizing the host tissue surface.
  13.  To study the flagella under microscope we use Leifson’s method for staining.

Do all bacteria have flagella?

No, all bacteria do not have flagella.

Bacteria with free, self-motility usually are the ones with flagella.

What types of bacteria have flagella?

Both prokaryotic and eukaryotic bacteria have flagella, irrespective of whether they are gram-positive or gram-negative.

Most gram-negative bacilli (e.g., E. coli; Salmonella etc.); gram-positive rods (e.g., Listeria; Clostridium etc.) and a few cocci (e.g., vagococcus) have flagella present.

Which bacteria do not have flagella?

Most of the capsular, non-motile bacteria do not have flagella.

Even various motile bacteria do not have flagella and usually move via gliding on the medium with help of Brownian movement. Cocci bacteria rarely possess any flagella. Bacteria without any flagella are called ‘Artichous bacteria’.

Do gram-positive bacteria have flagella?

Yes, gram-positive bacteria do possess flagella.

In case of gram-positive bacteria ring complex have 4 basal body rings one in cytoplasmic membrane, MS complex; one inside cytoplasm, C ring; one anchored in peptidoglycan layer, P ring and lastly one ring complex is attached in the lipopolysaccharide layer, L ring.

Do gram-negative bacteria have flagella?

Yes, gram-negative bacteria have flagella as well.

Unlike gram-positive bacteria, gram-negative bacteria do not possess a lipopolysaccharide layer, so they lack the L ring embedded in lipopolysaccharide layer.

Except that, gram-negative bacteria have a similar flagellar structure to gram-positive bacteria, including C, MS & P rings.

Do bacteria have periplasmic flagella?

Yes, bacteria belonging to the class Spirochete have periplasmic flagella.

Flagella, those are present inside the cell within periplasmic space, I.e., space between inner and outer cytoplasmic membrane, filled with a gel-like matrix; are known as periplasmic flagella. Rotation of these structures cause specific movements in cell resulting cellular motility.

Periplasmic flagella are also known as, endoflagellum.

How many flagella do bacteria have?

Bacteria can have one or multiple flagella present in either or both polar ends of bacterial cell, and even sometimes all over the cell surface,

Based on the position and number of flagella present bacteria are classified into four categories,

  1. Monotrichous- single polar flagellum present. e.g.: Vibrio cholerae.
  2. Amphitrichous– they single flagellum is present on each ends of cellular body. e.g.: Alkaligens faecalis.
  3. Lophotrichous- multiple flagella are present at either or both ends. e.g.: Spirillum spp.
  4. Peritrichous– numerous flagella present all over the bacterial body. e.g.: Salmonella typhi.
do bacteria have flagella
Fig: “Flagella arrangements” by Becky Boone is licensed under CC BY-SA 2.0. Copy text

Do non motile bacteria have flagella?

Non-motile bacteria do not possess flagella.

Though some bacteria without flagella can be motile, no bacteria that are non-motile, are in possession of flagella.

Without any need of locomotive movement, the evolutionary significances of flagella in non-motile bacteria are none. Without any uses, organisms will not develop any organelles that consume metabolic energy produced by respiration.

Does helical bacteria have flagella?

Yes, some helical bacteria have flagella.

Helical bacteria usually have periplasmic flagella for locomotive purposes. e.g., Helicobacter pylori.

Why do bacteria have multiple flagella on cell surface?

Except locomotion, the presence of numerous flagella help bacteria to attach to the host cell surface easily.

Do flagella triggers immune response?

Yes, inside host body bacterial flagella can cause immune response.

Flagellin protein when inside host body acts as a foreign antigen and can get recognized by lymphocytes. It can trigger antigen-antibody reaction resulting in immune response.

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