The bacterial flagellum has three main parts - the filament, basal body, and hook. The filament is the longest, rigid structure made of the protein flagellin. The basal body is embedded in the cell and contains protein rings. The hook connects the filament to the basal body. The basal body contains protein rings and a central rod that span the cell membranes. Rotation of the flagellum is driven by a motor composed of a rotor and stator. Proton motive force powers the motor and causes clockwise or counter-clockwise rotation for movement or tumbling.

1. ULTRA STRUCTURE OF
FLAGELLA
SUBMITTED BY
Vivek kumar
MSc . MICROBIOLOGY
Bangalore university

2. FLAGELLAR ULTRA
STRUCTURE
 Bacterial flagellum is composed of three parts.
 1) FILAMENT
The longest and most obvious portion, which extends
from the cell surface to the tip.
 2) BASAL BODY
The portion embedded in the cell.
 3) HOOK
A short, curved segment ,links the filament to its basal
body and act as a flexible coupling.

4. FILAMENT
 It is a hollow, rigid cylinder constructed of a single protein
called flagellin.
 Flagellin have a molecular weight ranging from 30,000 to
60,000.
 The filament ends with a capping protein.
 Some bacteria have sheaths surrounding their flagella.

5. BASAL BODY
 It is the most complex part of a flagellum.
 In gram negative bacteria, the body has 4 rings connected to
a central rod.
 The outer L ring is associate with lipopolysaccharide.
 The P ring is associate with the peptidoglycan layers.
 The inner M ring connects the plasma membrane.

6. HOOK
 It is quite different from filament.
 It is slightly wider than the filament.
 Hook is made up of different protein subunits.

7.  Gram positive bacteria have only 2 basal body
rings.
 An inner ring is connected to the plasma
membrane.
 An outer ring probably attached to the
peptidoglycan layer.

9.  Sometimes the flagellum will have lateral hairs called
flimmer filaments.
 The thicker, stiffer hair are called mastigonemes.
 These filaments change the flagella action.
 so that a wave moving down the filament towards the tip
pulls the cell along instead of pushing it.
 Such a flagellum is called tinsel flagellum.
 The naked flagellum is called whiplash flagellum.

11. FLAGELLAAND MOTILITY
 Most motile bacteria move by use of flagella.
 Its a thread like locomotor appendages extending outward
from the plasma membrane and the cell wall.
 They are slender, rigid structures, about 20 μm long.
 Flagella can be observed by using special staining
techniques.

12. FLAGELLAR
ARRANGEMENTS
MONOTRCHOUS FLAGELLA
Having one flagellum. If it is located at an end it is called
polar flagellum.
AMPHITRICHOUS FLAGELLA
Have a single flagellum at each pole.
LOPHOTRICHOUS FLAGELLA
Have a cluster of flagella at one or both ends.
PERITRICHOUS FLAGELLA
Flagella are spread fairly evenly over the whole surface

15. STRUCTURE OF FLAGELLA
 Flagella are membrane bound cylinders about 0.2 μm in
diameter.
 Located in the matrix of the organelle is a complex, the
axoneme.
 The axoneme consists of 9 pairs of microtubule doublets
arranged in a circle around 2 central tubules.
 This is called 9+2 pattern of microtubules.

17.  Each doublet also has pair of arms projecting from
subtubule A towards a neighbouring doublet.
 A radial spoke extends from subtubule A towards the
internal pair of microtubule with their central sheath.
 The microtubules are similar to those found in the
cytoplasm.
 It is constructed of α and β tubulins subunits.

19.  The basal body is a short cylinder with 9 microtubule triplets
around its periphery, a 9+0 pattern.
 Basal body is separated from the rest of the organelle by a basal
plate.
 The doublet arms, about 15nm long, are made of dynein protein.
 Dynein arms interact with the B subtubules of adjacent doublets
to cause the sliding.
 Radial spokes also participate in sliding motion.

21.  Flagella beats at a rate of about 10 to 40 strokes of
waves per second.
 The common euglenoid flagellate, Euglena gracilis
travels at around 170 μm per second.
 The flagellate Monas stigmatica, swims at a rate of
260 μm / second.

22. FLAGELLAR SYNTHESIS
 It is a complex process involving at least 20 to 30 genes.
 Besides the gene for flagellin, 10 or more genes code for
hook and basal body proteins.
 Filament synthesis is an example of self-assembly.
 The information required for filament construction is present
in the structure of the flagellin subunit itself.

23.  The MS ring is synthesised first and inserted into the
cytoplasmic membrane, this is followed by the
formation of other rings, hook and cap.
 These flagellin molecules are then assisted by cap
protein which exist at the tip of a growing flagellum.
 Self-assembly or aggregation of flagellin proteins
lead to the formation of filaments
• The flagellin subunits are transported through the
filament's hollow internal core.

25. Self assembly of flagellin filaments

26. Mechanism of flagellar movement
 The filament is in the shape of a rigid helix, and the
bacterium moves when this helix rotates.
 Flagella act like a propellers of a boat.
 The flagellar motor can rotate very rapidly.
 the direction of flagellar rotation determines the
nature of bacterial movements.

27.  Polar flagella rotate counter clockwise during normal
forward movement.
 The cell itself rotates slowly clockwise.
 The rotating filament thrusts the cell forward with
the flagellum trailing behind.
 Monotrichous flagella stop and tumble randomly by
reversing the direction of flagellar rotation.

28.  Peritrichous flagella operate in somewhat similar
way.
 To move the flagella rotates counter clockwise.
 They bend as their hook to form a rotating bundle
that propels them forward.
 Clock wise rotation of the flagella disrupts the
bundle and the cell tumbles

31.  Because bacteria swim through rotation of their rigid
flagella, there must be some sort of motor at the
base.
 The flagellum rotate because of interactions between
the S and M ring, which can rotate freely in the
plasma membrane.
 Torque generated by the motor is transmitted by the
basal body to the hook and the filament

32. MOTOR
 It is composed of two components
1. THE ROTOR
2. THE STATOR
 It function like an electrical motor, where the rotor turns in
the centre of a ring of electromagnets, the stator.
 In gram negative bacteria, the rotor is composed of the MS
ring and the C ring.
 The flagellar protein FliG is important to interact the rotor
with the stator.

33. The rotor
 In gram negative bacteria, the rotor is
composed of the MS ring and the C ring.
 The flagellar protein FliG is important to
interact the rotor with the stator.

34. The stator
 The stator is composed of the proteins MotA
and MotB.
 Both form a channel through the plasma
membrane .
 MotB also anchor MotA to cell wall
peptidoglycan.

35.  A proton motive force is used to generate torque.
 The channel created by MotA and MotB proteins
allow protons to move across the plasma membrane
from outside to inside.
 They move to the charge and pH gradient.
 This movement releases energy that is used to rotate
the flagellum.

36. Mechanism of flagellar movement

37. PERIPLASMIC FLAGELLA
 Certain helical bacteria exhibit swimming motility
particularly in highly viscous media.
 They lack external flagella but possess flagella like
structures located within the cell just beneath the
outer cell envelope.
 These are called periplasmic flagella or endoflagella
or axial flagella.

38. Periplasmic flagella

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