Bacteria have a simple but well-developed cell structure that allows them to survive and carry out essential functions. The three main components of the bacterial cell are the cell envelope, cell membrane, and cytoplasm. The cell envelope provides structure and protection, and its composition differs between Gram-positive and Gram-negative bacteria. Within the cell are additional structures that carry out key roles such as protein synthesis, DNA replication, and nutrient storage and transport. Some bacteria also possess non-essential structures like flagella, pili, and capsules that contribute to motility, adhesion, and virulence.

1. The Bacterial Cell
MORPHOLOGY OF BACTERIA
1

2. Key Words
Prokaryote Outer membrane
Eubacteria (Bacteria) Periplasmic space
Archaebacteria (Archaea) Oxidative phosphorylation
Eukaryote Spheroplast/protoplast
Plasmid Flagella
Chromosome Chemotaxis
Ribosome Axial filament
Peptidoglycan (murein, mucopeptide) Storage Granules
Gram stain
Gram negative Pili (fimbriae)
Endospore (spore)
Gram positive
Cell envelope Capsule (slime layer, glycocalyx)
Cell membrane
Cell wall
2

3. EUKARYOTES
PROKARYOTES
EUBACTERIA ARCHAEA
3

4. Prokaryotes (Bacteria)
• Eubacter "True" bacteria
– human pathogens
– clinical or environmental
– one kingdom
• Archaea
– Environmental organisms
– second kingdom
4

5. Introduction
• Bacteria despite their simplicity, contain a
well developed cell structure which is
responsible for many of their unique
biological properties. Many structural
features are unique to bacteria and are not
found among eukaryotes.

6. Cell Morphology
• The most elemental structural property of bacteria is cell
morphology (shape).
• Bacteria are classified by shape into three basic groups:
• cocci (spherical)
• bacilli (rod-like)
• spirochetes (spiral)
• Some bacteria are variable in shape and said to
pleomorphic.
• The shape of a bacteria is determined by its rigid cell wall.
• The microscopic appearance of a bacterium is one of the
most important criteria used in identification.

7. Bacteria come in a wide variety of shapes

8. • The arrangement of bacteria is important.
Example:
• Cocci in pairs (diplococci)
• Cocci in chains (streptococci)
• Cocci in clusters (staphylococci)

9. Bacteria Size
• Bacteria range in size from about 0.2 to 5
um.
• The smallest bacteria (Mycoplasma) are the
same size as a large virus.
• The longest bacteria rods are the same size
as some yeasts and human red blood cells.

10. CLASSIFICATION OF
BACTERIA
• ON BASIS OF SHAPE
• ON BASIS OF ARRANGEMENT
• ON BASIS OF STAINING
• ON BASIS OF OXYGEN
REQUIREMENT
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11. MORPHOLOGY OF BACTERIA
(SHAPE)
• COCCI -- round
• BACILLI-- rods
• SPIROCHETES-- spiral
• PLEOMORPHIC
11

12. ARRANGEMENT OF
BACTERIA
• CHAINS
• CLUSTERS
• PAIRS
• TETRADS
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13. STAINING OF BACTERIA
• GRAM’S STAINING
Gram positive
Gram negative
Gram variable
13

14. ON BASIS OF OXYGEN
REQUIREMENT
• Aerobes
• Anaerobes
• Facultative anaerobes
etc
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15. STRUCTURE OF BACTERIA
• ESSENTIAL STRUCTURES
• NON-ESSENTIAL STRUCTURES
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16. Essential structures
• Cell envelope:
Cell wall (except Mycoplasma)
Cell membrane
• Ribosome
• Nucleoid
• Mesosome
• Periplasm ( in gram’s negative bacteria)
16

17. Non Essential structures
• Capsule
• Pilus
• Flagellum
• Spore
• Plasmid , Transposons
• Granule
• Glycocalyx
17

18. Bacterial Structure

19. Cell Structure

20. CELL ENVELOPE
KEY WORDS
Cell envelope
• Cell wall
• Cell membrane
20

21. Cell envelope
– The cell envelope: Consists
of cell membrane and cell
wall plus an outer
membrane if present.
– Most bacterial cell
envelopes fall into two
major categories: Gram
positive and Gram
negative based on Gram
staining characteristics
that reflect major
structural differences 21
between the two groups

22. GRAM POSITIVE CELL
ENVELOPE
Lipoteichoic acid Peptidoglycan-teichoic acid
Cytoplasmic membrane
Cytoplasm
22

23. GRAM NEGATIVE
CELL ENVELOPE
Outer Membrane
(Major permeability barrier) Lipopolysaccharide
Porin
Braun lipoprotein
Periplasmic space
Periplasmic binding protein
Inner (cytoplasmic) membrane Permease
Cytoplasm 23

24. Cell Walls
Depending on Structure of their cell walls, the bacteria absorb either the
purple dye or the pink dye.

25. Prokaryotic cell
Cell membrane Cell wall
Gram +
Gram -
Cell (inner) membrane Outer membrane
Cell wall 25

26. Cell wall
• Cell wall consists of
 the peptidoglycan layer
 attached structures
(eg: capsule, pili etc)
26

27. PEPTIDOGLYCANS ( murein/ mucopeptide)
– Multilayered in gram positive bacteria.
– Surrounds the bacterial cell membrane.
– Provides rigidity. It is huge (billions in molecular weight)
– Consists of a glycan (polysaccharide) backbone with peptide
side chains.
– PG is found in all bacteria except Chlamydia and
Mycoplasma.
27

28. Gram positive cell
envelope:
Thick peptidoglycan
with covalently bound
teichoic acid.
These negatively
charged molecules
concentrate metal
ions from the
surroundings.
Lipoteichoic acid is
primarily associated
with the cell
membrane. 28

29. Gram negative cell envelope
• Outer membrane present
( lipopolysachride, lipoprotein &phospholipid) ---
endotoxin
Lipid A --- toxic
Polysaccharide core
Outer polysaccharide -- antigenic
• Thin peptidoglycan layer
• No teichoic acid
• Periplasmic space : b/w two membranes 29

30. Gram negative cell envelope
• Porin protein
30

31. GRAM POSITIVE
Lipoteichoic acid Peptidoglycan-teichoic acid
Cytoplasmic membrane
Cytoplasm
GRAM NEGATIVE Porin
Lipopolysaccharide
Periplasmic space
Outer Membrane Braun lipoprotein
Inner (cytoplasmic) membrane
Cytoplasm 31

32. CELL MEMBRANE
.
Cell Wall
Cytoplasm
Cell membrane
•Oxidative phosphorylation (no mitochondria).
•Synthesis of cell wall precursor.
•Active transport
•Synthesis of enzymes. 32

33. CYTOPLASM
• Mesosome
 Cytoplasmic membrane invagination.
 Cell division-----DNA binding site.
Ribosomes
 70S in size (50S & 30S)
 Protein synthesis.
Nucleoid
• No nuclear membrane.
• DNA---Single, circular, about 2000 genes.
• No introns in DNA, no mitotic spindle, no 33
nucleolus, no histones

34. Non Essential structures
• Capsule
• Pilus
• Flagellum
• Spore
• Plasmid , Transposons
• Granule
• Glycocalyx
34

35. Capsules and slime layers
(Glycocalyx)
• well defined: capsule
• outside cell envelope
• usually polysaccharide (in B. anthracis– D
glutamate)
• Gives virulance (antiphagocytic).
• Antigenic (vaccine formation).
• Adherence.
• Quellung reaction (Identification).
2. not well defined-- slime layer or glycocalyx
o Adherence
35
o S.mutans (Plaque formation)

36. FLAGELLA
• For motility – long & whip like
• Subunits—Flagellin
• Respond to food/poison –chemotaxis
• Never present in cocci.
• Use ATPs – proton motive force
• Number and location of flagella.
(Peritrichous, monotrichous,
lophotrichous, axial). 36

37. • Flagella
–embedded in cell membrane
–project as strand
–Flagellin (protein) subunits
–move cell by propeller like action
–*axial filament
–*flagellar antigen
37

38. Flagella
A-Monotrichous; B-Lophotrichous;
C-Amphitrichous; D-Peritrichous;

39. Axial filaments
– spirochetes
– similar function to flagella
– run lengthwise along cell
– snake-like movement
39

40. Pili (fimbriae)
•Short , hair-like projections of the cell
•Protein--pilin
•Mostly on gram-ve bacteria
•adhesion to host epithelium
•Two types– ordinary pili
sex pili
•sexual conjugation (sex pili)
40

41. Endospores (spores)
• Metabolically dormant cell
• Produced when adverse conditions eg starved –
sporulation – bacterial DNA, cytoplasm, cell
membrane, peptidoglycans, water & keratin- like coat
• Resistant to adverse conditions
- high temperatures (not killed by boiling),
- radiation, dehydration
- organic solvents
• Killed by autoclaving (121 C for 30 min)
• contain dipicolinic acid
• Bacillus (central) and Clostridium (terminal)
• Survival for many years 41

42. CYTOPLASM
Granules
– Storage of nutrients
– Stained with dyes
Transposons
 Jumping genes – within DNA or between DNAs of
bacteria, plasmids & bacteriophages
 Pieces of DNA
 No independent replication.
 Can be more than one in 1 DNA.
 For toxins, enzymes, antibiotic resistance etc.
 4 domains– inverted repeats, transposase, repressor,
resistance. 42

43. Plasmids
 Multiple copies in number
 Extra-chromosomal DNA, double
stranded, circular
 Can be incorporated in DNA
 Coding pathogenesis and antibiotic
resistance, heavy metal & U-V light
resistance, toxins, pili etc.
 Replication independent of bacterial
chromosome.
Transmissable & Non transmissable. 43

44. Making Wall-less forms
• Result from action of:
– enzymes lytic for cell wall (eg lyzozyme)
– antibiotics inhibiting peptidoglycan biosynthesis
• Wall-less bacteria that don’t replicate:
– spheroplasts (with outer membrane) gram - ve
– protoplasts (no outer membrane) gram +ve.
• Wall-less bacteria that replicate
– L forms ( relative resistance to antibiotics)
44

45. Naturally Wall-less Genus
• Mycloplasma
45

46. The Cell Envelope
Gram Positive Gram Negative
46

47. GRAM STAIN
• Gram positive
• Gram negative
• Gram variable
47

48. Procedure
of Gram Staining
• Developed by Christian Gram
• In 1884
• 4 steps:
 Stain with Crystal voilet (primary stain)
 Then pour Gram,s iodine (mordant)
 Decolourize
 Pour Safranin (counter stain)
48

49. Gram negative Gram positive
Heat/Dry
Crystal violet stain
Iodine Fix
Alcohol de-stain
de
Safranin stain
49

50. Gram stain morphology
• Shape
– cocci (round)
– bacilli (rods)
– spiral or curved (e.g. spirochetes)
• Single or multiple cells
– clusters (e.g. staphylococci)
– chains (e.g. streptococci)
• Gram positive or negative
50

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