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1. Morphology and Structure of
Bacteria
Md. Saiful Islam
Dept. of Pharmaceutical Sciences
North South University
Facebook Group: Pharmacy Universe
YouTube Channel: Pharmacy Universe

2. TYPICAL STRUCTURE OF BACTERIA

3. Morphological Characteristics
 The major morphological characteristics of bacteria include: (1)
size (2) shape (3)structure and (4) arrangement of bacterial
cells.
 The basic shapes that occur are: (1) spherical (2) rodlike and
(3) helical.
 In certain species of bacteria, the cells are arranged in pairs,
clusters, chains, trichoma and filaments.
 The pattern, shape and arrangement are often characteristic of
genus.

4. Morphological Characteristics
These are the spherical "Cocci" bacteria This is an example of the rod shaped
"Bacillus"
These are the spiral (helical) shaped "spirillia" type of bacteria.

5. Morphological Characteristics
 The internal structure of the cell was made
possible by the development of the electron
microscopy and of the instruments for slicing
bacterial cells into extremely small sections.
 The various structures of bacterial cells can
differ from one another by physical features
and chemical characteristics.

6. Size
Size of bacterial cells:
 Most bacteria are approximately 0.5µm to
1µm.
 The surface area/volume ratio is very high as
compared to larger organisms of similar
shape.
 High surface area accounts for high rate of
growth and metabolism of bacteria.

7. Shape and Arrangement
Shape and Arrangement of bacteria:
 The shape of a bacterium is governed by it rigid cell
wall.
 The typical bacterial shapes are:
 (1) Spherical: cocci (singular: coccus)
E.g. Stapylococcus
 (2) Staright rods: bacilli (singular: bacillus)
E.g. Lactobacillus
 (3) helical rods: spirilla (singular: spirillum)
E.g. Aquaspirillum

8. Shape and Arrangement of bacteria
Scanning electron microscopy
of Staphylococcus
epidermidis cluster embedded in
exopolysaccharide matrix
Electron Micrograph of the Meat
Spoilage
Bacterium Lactobacillus sake
Aquaspirillum
magnetotacticum

9. The three major shapes of bacteria

10. Shape and Arrangement
Characteristic arrangement of cocci:
 Diplococci: cells divide in one plane and
remain attached predominantly in pairs.
 Streptococci: cells divide in one plane and
remain attached to form chains

11. Shape and Arrangement
 Tetracocci: cells divide in two planes and
characteristically form groups of four cells.
 Staphylococci: cells divide in three planes in an
irregular pattern producing bunches of cocci.

12. Shape and Arrangement
 Sarcinae: cells divide in three planes in a
regular pattern producing a cuboidal
arrangement of cells.

13. Shape and Arrangement
Size and Shape: Size varies from 0.2 - 60 µm.
There are 4 basic shapes - spherical, rods, spiral and square.
Spherical is called coccus.
• Division along the same plane forms chains;
2 cocci together – Diplococcus
• 4 - 20 in chains Streptococcus.
• Division along 2 different planes-Tetrads
• Division along 3 planes regularly -
Sarcinae
• Division along 3 planes irregularly -
Staphylococci

14. Cocci
Neisseria Meningitidis (large
gram-negative diplococci)
Scanning electron microscope
image of Streptococcus bacteria/
encarta.com
Staphylococcus aureus
Electron micrograph of a cross-section
of a D. radiodurans tetracoccus (cluster
of four cells).
cocci, in cubes of eight
called "sarcinae

15. Shape and Arrangement
 Some bacillus species are lined side by side like
match sticks (palisade arrangement) and at angles to
one another.
E.g. Corynebacterium diptheriae
 Streptomyces species form long branched
multinucleate filaments called hyphae which
collectively form mycellium.
 Other shapes include curved bacteria, pear-shaped
cells, lobed spheres, disks arranged like stacks of
coins, etc.

16. Structures External to the Cell
Wall
(A) Flagella:
 Bacterial flagella (singular: flagellum) are hair-like structures that
protrude through the cell wall and are responsible for swimming
motility.
 The location of flagella may be polar (at one or both ends of
the bacterium) or lateral (along the sides of the bacterium).
 The flagella consists of three parts:
 (1) a basal body: associated with the cytoplasmic membrane
and short hook.
 (2) a short hook
 (3) a helical filament: which usually surrounds the flagellum

 The hook and the filament are made up of the protein called
flagellin.

17. Motility of Bacteria
 Presence of Flagella aids in motility: Bacteria having
polar flagella swim in back and forth fashion while
bacteria having lateral flagella swim in a more
complicated manner.
 Swimming motility without flagella: Some helical
bacteria exhibit swimming motility particularly in viscous
media even though they do not have flagella. Some
bacteria contain flagella-like structures beneath the outer
cell envelope (periplasmic flagella) and others are able
to swim in viscous media even without any periplasmic
flagella.

18. Motility of Bacteria
 Gliding motility: some bacteria are motile
only when they are in contact with the solid
surface. Movement is very slow and
mechanism of gliding motility is unknown.
 Bacterial chemotaxis: Many motile bacteria
are capable of directed swimming towards or
away from various chemical compounds by a
phenomenon called bacterial chemotaxis.

19. Flagella

20. Structures External to the Cell
Wall
(B) Pili (Fimbrae):
 Pili (singular: pilus) are hollow, non-helical,
filamentous appendages that are thinner, shorter and
more numerous than flagella.
 They are found both in motile and non-motile bacteria
and do not function in motility.
 They have various functions: e.g. pili help bacteria to
attach to epithelial cells during infection and prevents
bacteria from being washed away by the flow of body
fluids.

21. Structures External to the Cell
Wall
(C) Capsules:
 some bacterial cells are surrounded by a viscous
substance forming a covering layer around the cell wall.
This is called a capsule.
 If the layer is too thin it is called a microcapsule.
 If it is so abundant that many cells are embedded in a
common matrix then it is called slime.
 Some of the functions of capsules are:
 (1) They provide temporary protection to bacteria
against drying.
 (2) They may block he attachment of bacteriophages.
 (3) They may be antiphagocytic.

22. Pili and Capsule

23. Cell Wall of Bacteria
Cell wall
 Beneath the external structures (capsules,
falgella) and external cytoplasmic membrane
is the cell wall.
 Cell wall is a very rigid structure that gives
shape to the cell.
 Its main function is to prevent the cell from
expanding and eventually bursting because of
uptake of water.

24. Cell Wall of Bacteria
Structure and chemical composition of cell walls of
different types of bacteria:
 Peptidoglycan: the shape determining part of the cell wall
in eubacteria is largely peptidoglycan (sometimes called
murein).
 Peptidoglycan is an insoluble, porous, cross-linked
polymer of enormous strength and rigidity.
 Peptidoglycan is found only is prokaryotes.
 Composition of peptidoglycan: N-acetyl glucosamine,
N-acetyl muramic acid, L-alanine, D-alanine, D-glutamate
and a diamino acid (meso-diaminopimelic acid, L-lysine,
L-ornithine or L-diaminobutyris acid).

25. Peptidoglycan Matrix

26. Cell Wall of Bacteria
Walls of Archeobacteria:
 The cell walls of archeobacteria do not contain peptidoglycan.
 Their cell wall structure and composition are very different from
eubacteria.
 Theirs walls are usually composed of proteins, glycoproteins
and polysaccharides.
Walls of Gram positive eubacteria:
 High amount of peptidoglycan is present.
 They may contain polysaccharides covalently bound to
peptidoglycan.
 Techoic acid may be present.

27. Cell Wall of Bacteria
Walls of Gram negative eubacteria:
 Cell walls of Gram negative bacteria are more complex than
those of Gram positive bacteria.
 Presence of an outer membrane rich in lipid which serves as a
barrier to prevent the escape of important enzymes.
 Composition: phospholipids, proteins and lipopolysaccharides.
Macromolecular surface arrays:
 The cell walls of some of the gram positive and gram negative
bacteria are covered by a mosaic layer of protein subunits.

28. CELL WALLS OF GRAM POSITVE AND GRAM NEGATIVE
BACTERIA

29. Structures Internal to the Cell Wall
(A) Cytoplasmic membrane:
 The cytoplasmic membrane lies immediately beneath the cell
wall.
 It is approximately 7.5 nm thick and is composed of
phospholipid which form a bilayer and hold integral proteins.
 The lipid matrix of the membrane has fluidity which allows the
components to move around laterally.
 Functions of the membrane include: (1) it acts as a hydrophbic
barrier preventing penetration of water-soluble molecules. (2)
Contains enzymes involved in respiratory metabolism and
synthesis of various cell-components.
 Damage to the cytoplasmic membrane by physical or chemical
means can result in cell death.

30. Cell Wall of Gram positive bacteria

31. Structures Internal to the Cell Wall
(B) Protoplasts and Spheroplasts:
 Protoplasts and spheroplasts function in maintaining the
osmotic pressure of the bacterial cell.
(C) Membranous intrusions and intracellular membrane
Systems:
 Bacterial cells do not contain membrane-enclosed organelles.
Rather they have specialized invaginations of the cytoplasmic
membrane that can increase the surface area for certain
functions. Mesosomes refer to the invaginations which are
involved in cell division or export of exocellular enzymes.
(D) Cytoplasm:
 It is the cell material bounded by the cytoplasmic membrane.

32. Structures Internal to the Cell Wall
 Cytoplasm is divided into: (1) the cytoplasmic area:
granular in appearance and rich in ribosomes. (2)
chromatinic area which is rich in DNA and (3) fluid
portion with dissolved substances.
(E) Cytoplasmic inclusions and vacuoles:
 These are concentrated deposits of certain
substances in the cytoplasm.
 E.g. Volutin granules: reserve source for phosphate
 Polysaccheride granules: glycogen reserve.
 Gas vacuoles: provide buoyancy.

33. Structures Internal to the Cell Wall
(F) Nuclear material:
 Bacterial cells neither contain distinct
membrane enclosed nucleus nor a mitotic
apparatus.
 They contain a nuclear structure in the center
of the cell where DNA is confined.
 Nucleoid, chromatin body and bacterial
chromosome all refer to the nuclear material
in bacteria.

34. Structure of Bacteria

35. Spores and Cysts
Spore:
 The spore is a metabolically dormant form which, under appropriate
conditions, can undergo germination and outgrowth to form a
vegetative cell.
Endospores:
 Production of spores within the cell.
 Produced by cells growing in rich media but which are approaching
the end of active growth.
 The genera Bacillus, Clostridium, Sporosarcina and
Thermoactinomyces are examples which can produce endospores.
 All endospores contain dipocholinic acid (DPA) which is not present
in vegetative cells.
 Endospores are resistant to desiccation, staining, disinfecting
chemicals, radiation and heat.

36. Spores and Cysts
Exospores:
 Spores external to the vegetative cell.
 These are desiccation-resistant and heat-resistant but do
not contain DPA.
 Cells of methane-oxidizing genus Methylosinus form
exospores.
Cysts:
 Cysts are dormant, thick walled, desiccation-resistant
forms that develop by differentiation of a vegetative cell
and which can later germinate under suitable conditions.
 An example of a cyst is the structurally complex type
produced by the genus Azobacter.

37. Exospore and endospore
Endospore formation
Cysts in Azobacter

38. STRUCTURE FUNCTION
Cell Wall protects the cell and gives shape
Outer Membrane protects the cell against some antibiotics (only present in Gram-negative cells)
Cell Membrane
regulates movement of materials into and out of the cell; contains enzymes
important to cellular respiration
Cytoplasm contains DNA, ribosomes, and organic compounds required to carry out life processes
Chromosome carries genetic information inherited from past generations
Plasmid contains some genes obtain through genetic recombination
Capsule, and slime layer protects the cell and assist in attaching the cell to other surfaces
Endospore
protects the cell against harsh environmental conditions, such as heat or
drought
Pilus (Pili) assist the cell in attaching to other surfaces, which is important for genetic recombination
Flagellum moves the cell
STRUCTURAL CHARACTERISTICS OF A BACTERIAL CELL

39. Shape and Arrangement of Cocci