Difference between Pili and Flagella of Bacteria- A Comparison Table

Fimbria vs pilus

Flagella vs Pili of Bacteria: A Comparison Table
(Similarities and Differences between Pili and Flagella of Bacteria)

Both Flagellum (plural Flagella) and Pilus (plural Pili) are the filamentous proteinaceous structures found on the surface of some bacterial cells. They extend from the surface of the bacterial cell wall and can have many functions such as motility, attachment, adhesion and assisting in genetic exchange.

Flagella definition: Bacterial flagella are long whip-like filamentous structures present in some bacteria. The most important function of flagella is to assist in locomotion. Flagella can also act as a sensory organ to detect temperature and the presence of certain chemicals in the external environment of the cell. Even though the flagella are present in prokaryotes and eukaryotes, both are entirely different in their structure, formation and mechanism of propulsion.

Pili definition: Pili are long hair like tubular micro-fibres like structures present on the surface of some Gram-negative bacteria. They are comparatively shorter filamentous structures than flagella and their number per cell is very limited. There are many classes of pili based on their structure and function. Most of the pili can act as the receptors of some viruses.

The present post describes the Similarities and Differences between Flagella and Pili with a Comparison Table

Similarities between Flagella and Pili

Ø  Both flagella and pili are filamentous structures.

Ø  Both are cell surface appendages.

Ø  Both are made up of proteins.

Ø  Number of both flagella and pili are limited per bacterial cells.

Ø  Both flagella and pili are tubular hollow structures.

Difference between Flagella and Pili

Sl. No.FlagellaPili
1Flagella are long whip-like filamentous structures occur on the surface of some bacteria.Pili are long hair like tubular microfibres like structures present on the surface of bacteria.
2Flagella is present in both Gram positive and Gram-negative bacteriaPili are presently only in Gram-negative bacteria
3Examples of bacteria having Flagella:
Escherichia coli, Helicobacter pylori, Salmonella typhimurium.
Examples of bacteria having pili
Escherichia coli, Neisseria gonorrhoeae, Pseudomonas.
4Flagella are made up of flagellin protein.Pili are made up of pilin protein
5Flagella are interior in their origin, originated from the cytoplasmic membrane.Pili are external in origin, originated from the cell wall of bacteria.
6The formation of flagella is controlled by genes present in the nucleoid region of the bacteria.The formation of pili is controlled by the gene present in plasmids.
7Flagella are helical and non-straight in nature.Pili are straight and non-helical in nature.
8Flagella are many times longer than Pili.Pili are comparatively shorter than flagella.
9Approximate length of flagella highly varies. (it is about 15 to 20 µm).Approximate length of pili is 0.5 – 2 µm.
10Flagella usually show a distinct pattern of distribution. Distribution may be polar, lateral or throughout the surface. Pili are randomly distributed on the surface of bacteria
11Flagella are comparatively thicker than Pili.Pili are comparatively thinner than flagella.
12Flagella are more rigid structures than pili.Pili are less rigid when compare to flagella.
13The main function of flagella is locomotion. Some flagella act as the sensory organ. Flagella do not have any role in surface attachment.The function of pili varies; The main function of pili is gene transfer (by conjugation) and attachment. Some pili such as Type IV pili show the twitching type of mobility.
14Bacterial flagella are always associated with a complex motor system at the base for propulsion.There is NO motor system associated with pili
15Flagella do not have any role in genetic exchange between organismA class of pili called sex pili acts as the conjugation tube for the transfer of genetic material between two different bacterial strains during conjugation.
16No flagella is reported to act as the receptors of virusesMost of the pili can act as receptors for different types of viruses.

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