Flagella vs Pili 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.

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BOTANY	BIOCHEMISTRY	MOL. BIOLOGY
ZOOLOGY	MICROBIOLOGY	BIOSTATISTICS
ECOLOGY	IMMUNOLOGY	BIOTECHNOLOGY
GENETICS	EMBRYOLOGY	PHYSIOLOGY
EVOLUTION	BIOPHYSICS	BIOINFORMATICS

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.	Flagella	Pili
1	Flagella 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.
2	Flagella is present in both Gram positive and Gram-negative bacteria	Pili are presently only in Gram-negative bacteria
3	Examples of bacteria having Flagella: Escherichia coli, Helicobacter pylori, Salmonella typhimurium.	Examples of bacteria having pili Escherichia coli, Neisseria gonorrhoeae, Pseudomonas.
4	Flagella are made up of flagellin protein.	Pili are made up of pilin protein
5	Flagella are interior in their origin, originated from the cytoplasmic membrane.	Pili are external in origin, originated from the cell wall of bacteria.
6	The 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.
7	Flagella are helical and non-straight in nature.	Pili are straight and non-helical in nature.
8	Flagella are many times longer than Pili.	Pili are comparatively shorter than flagella.
9	Approximate length of flagella highly varies. (it is about 15 to 20 µm).	Approximate length of pili is 0.5 – 2 µm.
10	Flagella 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
11	Flagella are comparatively thicker than Pili.	Pili are comparatively thinner than flagella.
12	Flagella are more rigid structures than pili.	Pili are less rigid when compare to flagella.
13	The 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.
14	Bacterial flagella are always associated with a complex motor system at the base for propulsion.	There is NO motor system associated with pili
15	Flagella do not have any role in genetic exchange between organism	A class of pili called sex pili acts as the conjugation tube for the transfer of genetic material between two different bacterial strains during conjugation.
16	No flagella is reported to act as the receptors of viruses	Most of the pili can act as receptors for different types of viruses.

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@. Difference between Fimbriae and Flagella

@. Difference between Fimbriae and Pili

@. Difference between Gram Positive and Gram Negative Bacteria

@. Comparison Table of Archaea, Bacteria and Eukarya