Bacteria are classified according to their shape into three main categories: spherical (cocci), rod-shaped (bacillus), and spiral (spirillum). Their cell structure includes a capsule, cell wall, cell membrane, cytoplasm containing nuclear material and ribosomes, and sometimes appendages like flagella or pili. Some bacteria form dormant endospores to survive harsh conditions, which have a highly resistant structure including a core, cortex, coat, and sometimes exosporium.

1. Bacterial Morphology

2. Introduction
• Bacteria belong to the kingdom Monera. They are
unicellular organisms
• They are classified according to three shapes
1. Spherical (cocci)
2. Rod (bacillus)
3. Spiral (spirillum)

5. Spherical (cocci)
E.g. Staphoolococcus aureus
Causes pneumonia

6. Rod (bacillus)
• E.g. Bacillus anthracis
• Cause of anthrax
• Escherichia coli (E.coli)
• Live in human gut

7. Spirillum (spiral)
• E.g.Treponema pallidum
• Causes syphilis

8. Bacterial cell structure
• Surface layers - capsule, cell wall, cell
membrane
• Cytoplasm - nuclear material, ribosome,
mesosome, inclusion bodies etc.
• Appendages - fllagella, pili or fimbriae
• Special structure - endospore

9. Bacterial cell structure

10. Bacterial cell

11. Surface layers
1. Capsule.
2. Cell wall.
3. Cell membrane.

12. 1. Capsule and Slime layer
 These are structures surrounding the outside of the cell
envelope. They usually consist of polysaccharide; however, in
certain bacilli they are composed of a polypeptide
(polyglutamic acid). They are not essential to cell viability and
some strains within a species will produce a capsule, whilst
others do not. Capsules are often lost during in vitro culture.
Functions:
 Attachment
 Protection from phagocytic engulfment.
 Resistance to drying.
 Depot for waste products.
 Reservoir for certain nutrients.
 Protection.

13. Capsule

14. 2. Cell wall
Next lecture

15. 3. Cell Membrane
Function:
a. Control permeability
b. Transport electrons and protons for cellular metabolism.
c. Contain enzymes to synthesis and transport solute into the
cell.
d. Secret hydrolytic enzymes
e. Site of biosynthesis of DNA, cell wall polymers and membrane
lipids.
f. Electron transport and oxidative phosphorylation.

16. Cell membrane

17. Functions of cell membrane

18. Functions of cell membrane

19. Cytoplasm
• Composed largely of water (80%).
1. Nuclear material.
2. Ribosome.
3. Mesosome.
4. Plasmids
5. Inclusion bodies etc.

20. 1.Nucleic material
• Lacking nuclear membrane, absence of nucleoli,
hence known as nucleic material or nucleoid, one to
several per bacterium.
• A single large circular double stranded DNA no
histone proteins. The only proteins associated with
the bacterial chromosomes are those for DNA
replication, transcription etc.

22. 2. Ribosome
• Numerous in number.
• 15-20nm in diameter withwith70S.
• Distributed throughout the cytoplasm.
• Sensitive to streptomycin and erythromycin
site of protein synthesis.

24. 3. Mesosome
• Mesosomes are specialized structures formed by convoluted
invaginations of cytoplasmic membrane.
• Divided into septal and lateral mesosome.
• Irregular in shape.
Functions
a. Increase in membrane surface, which may be useful as a site
for enzyme activity in respiration and transport.
b. May participate in cell replication by serving as a place of
attachment for the bacterial chromosome

26. 4. Plasmids
• Plasmids are small, circular,
extrachromosomal ， double-stranded DNA
molecule.
• They are capable of self-replication.
• They contain genes that confer some properties,
such as antibiotic resistance, virulence factor.
• Plasmids are not essential for cellular survival.

27. 5.Inclusion bodies
Many bacteria have a variety of granules in their cytoplasm.
These granules are store deposits of nutrients like phosphate, sulphur and fats etc.
Examples
Granules of various kinds:
* Glycogen granules, they can be stained with iodine, as they are polysaccharides.
*poly B- hydroxybutyrate inclusion bodies (PHB) are carbon reservoirs, providing
energy for biosynthesis.
* Volutin granules (metachromatic granules) are made up of polyphosphate.
in general, starvation of cell for almost any nutrients leads to the formation of this
to serve as an intracellular phosphate reservoir.

28. Appendages
The filamentous structures protruding from the cell
wall of a bacterial cell are called appendages. These
are of two types
1. Flagella
2. Pili or fimbriae

29. 1. Flagella
• Some bacterial species are mobile and possess
locomotory organelles - flagella.
• The diameter of a flagellum is thin, 20 nm, and long with
some having a length 10 times the diameter of cell. Due to
their small diameter, flagella cannot be seen in the light
microscope.
• Bacteria can have one or more flagella arranged in clumps or
spread all over the cell.

30. Ultra structure of Flagella
• Flagella consists of repeating units of a protein------- flagellin.
• Flagellin molecules assemble to form fibers.
• A flagellum is formed when three fibers twist to form a helix.
• Flagellum is made up of three parts (Electron Micrography).
1. Filament
2. Hook
3. Basal body

31. Filament

32. The structure of the bacterial flagella allows it to spin
like a propeller and thereby propel the bacterial cell;
clockwise or counter clockwise.
– Bacterial flagella provides the bacterium with
mechanism for swimming toward or away from
chemical stimuli, a behavior known as Chemotaxix,
chemosenors in the cell envelope can detect certain
chemicals and signal the flagella to respond.

33. The number and arrangements of flagella are variable.
Monotrichous. One flagella from one end. (Vibrio cholerae)
Lophotrichous. Tuft of flagella at one pole. (Pseudomonas)
Amphitrichous. Flagella at both ends. (spirillum serpens)
Peritrichous. Flagella arise from all over the surface. (E. coli)

34. 2. Pili or Fimbriae
• Shorter, straighter, thinner, non helical and numerous than
flagella.
• Mostly on gram - bacteria.
• They are usually found in large numbers over the cell surface,
arising from cell membrane.
• Structure: They have a hollow core and are composed of
proteins which can be dissociated into smaller units Pilin . It
belongs to a class of protein Lectin which bond to cell surface
polysaccharide.

35. Function
a. Conjugation: Specialized sex pilus or F pilus serves
for the attachment of two bacterial cell before
conjugation and act as conjugation tube.
b. Adhesion: Serves as attachment structures or
adhesins. E.g. E.coli have pili that help them to
adhere to intestinal lining and causes diarrhea.
c. Receptor site: Act as site for some bacteriophages.
Bacteriophages attaches to pili and transfer their
genetic information to bacterial cell.

36. Special Structure-----Endospore
 Dormant cell.
 Produced when starved.
 Resistant to adverse conditions, ultraviolet
radiation, high temperatures, extreme freezing and
chemical disinfectants.
 Organic solvents.
 Contain calcium dipicolinate DPA, dipicolinic acid.
 Mostly gram positive bacteria (Bacillus and
clostridium).

37. Structure and chemical composition
• Core
• Dipicolinic acid
• Spore Cortex
• Spore coat
• Exosporium

38. • Core: It is the centre of the spore that contains the
chromosomes, all components of proteins synthesizing
machinery, enzymes etc.
• Dipicolinic acid (DPA): It is a spore-specific chemical that
appears to help in the ability for endospores to maintain
dormancy. This chemical comprises up to 10-15% of the
spore's dry weight. It is present in association with high
amounts of calcium in the core. The heat resistance of the
endospore is due to Calcium dipicolinate.
• Spore wall: Inner most lining surrounding the core. It consists
of Peptidoglycan and becomes cell wall of germinating
vegetative cells.
• Cortex: Thickest layer of core envelope.

39. • Spore coat: The outer most impermeable layer
which confers resistance to the spore to antibacterial
chemical agents.
• Exosporium: It is the outer most membrane that
contains lipoproteins and some carbohydrates.

40. Detailed steps in endospore formation