Bacterial Locomotor Organelles – Flagella

Flagella is a LASH or Whip like appendage , arising from Cellbody of Prokaryotic and Eukaryotic Organisms

Main Function of the Flagella is Locomotion , but other than that it also functions as a Sensory Organelle.

Motility :

● Motility -Movement

● Swarming occurs with some bacteria

– Spreads across petri dishes

– Proteus species is the most evident

● This motility of bacteria occur in 2 different phenomenon :

~ Phototaxis – Movement of bacteria in response to Light This phototaxis is again of 2 types –

* Positive Phototaxis : Towards light
* Negative Phototaxis : Away from light

~ Chemotaxis – Movement of bacteria in response to light

This Chemotaxis is again of 2 types –

* Positive Chemotaxis : Towards Chemical
* Negative Chemotaxis : Away from Chemicals

Arrangement of Bacterial Flagella

● How many flagella does a bacteria have ?

● How are they arranged ?

● Do all Bacteria have flagella ?

● How does a flagella look like ?

● How does it help in movement of a bacteria ?

Classification of Bacteria based on arrangement of flagella . . .

● ATRICHOUS : Absence of Flagella

● MONOTRICHOUS : Presence of a Single Flagella at one end

● LOPHOTRICHOUS : Presence of “tuft” of Flagella at one end

● AMPHITRICHOUS : Presence of a single Flagella at both ends

● PERITRICHOUS : Presence of Flagella all over the cell surface .

Lactobacillus Vibrio




Examples of the bacteria based on the arrangement of flagella . . .

Atrichous : Lactobacilli ,Diptheria bacillus

Monotrichous : Vibrio cholerae

Lophotrichous : Pseudomonas

Amphitrichous : Spirillum

Peritrichous : Bacillus

Structure of a Flagella -Prokaryotes

● Flagellum , consists of a Basal body , Hook and a Main Filament .

● Basal Body or Basal Granule :200 to 500 A in diameter ,

● In gram -ve bacteria , basal ring has 2 sets of rings , i.e.,

~ Proximal set
~ Distal set

● Each set has 2 rings,and the four rings are- M-ring , S ring , P ring , L ring .

● The arrangement of these rings are from inside to outside .

● M-ring is anchored to Plasma membrane , and P- ring to the Peptidoglycan layer of the cell-wall.

● M-ring provides the “movement” to the flagella.

● The S-ring is the Static- ring .

● The P-ring is attached to the Peptidoglycan layer , and the L-ring to the Lipopolysaccharide layer of the membrane of the gram -ve .

● While in Gram +ve , there are only a only single set of rings ,No attachment to cell wall is seen .

● The inner rings are attached to the p.membrane.

Hook :

● The Hook,penetrates the cell-wall,and connects main Filament and Basal body .

● It allows the axis of the helix to point directly away from the cell.

Main Filament :

● The filament consists entirely of Protein, called “Flagellin”.

● This protein is either free or consists of very
low amounts of amino acid residues.

● These residues are of : – Proline, Histidine, Cysteine, Tryptophan


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