FYBSc-Microbiology SIWS College Mumbai University

1. BACTERIAL CYTOLOGY

4. CELL WALL
WHY STUDY-
Determines shape
Protects cell
Protection from toxic substances
Site of action for antibiotics
LOCATION-
Outermost, rigid layer

5. TYPES-based on Gram staining
• Gram Positive, purple colour
• Gram Negative, pink colour
(Christian Gram-1884)

6. Structural differences between
G+ve & G-ve cell wall
• 20-80% nm thick
peptidoglycan (murein)
• 2-7% nm thick
peptidoglycan

10. PEPTIDOGLYCAN STRUCTURE- G+ve
1. Amino sugars
N acetyl glucosamine & N acetyl muramic acid
(NAG & NAM)
2. Protein
3. Techoic acid

12. TECHOIC ACID

13. Mesh structure of peptidoglycan

16. GRAM NEGATIVE CELL WALL

20. BLP( Braun’s lipoprotein)
• Braun's lipoprotein found in some gram-negative cell
walls
• the most abundant membrane proteins
• It is bound by a covalent bond to the peptidoglycan
layer
• and is embedded in the outer membrane by its
hydrophobic head
• BLP tightly links the two layers and provides
structural integrity to the outer membrane.
• Braun's Lipoprotein consists of phospholipids and
Lipopolysaccharide.

23. Gram Negative Cell Wall-chemical
compostion
• Lipopolysaccharide (LPS)
Large, complex molecule with lipid & carbohydrate
1. Lipid A
2. Core polysaccharide
3. O side chains

26. Functions of LPS
• Give negative charge to the surface
• Helps in attachment
• Stabilize the membrane
• Create a permeability membrane
• Prevent entry of toxic substances
• O side chain protects bacteria
• Lipid A is toxic (endotoxin)- causes serious
septic condition in the body

27. Functions of LPS
• Outer membrane is more permeable
than pm due to porins
• Porins are proteinic in nature, tube
shaped, allows passage of molecules
smaller than 600-700d
• For larger molecules carrier proteins
are there

28. Periplasmic space in bacteria

29. Periplasmic space in bacteria
• Gram Positive
• Small
• Fewer proteins
• Proteins present,
attached to plasma
membrane
• Exoenzymes- degrade
polymeric nutrient
• Gram Negative
• Wide (30nm-70nm)
• More proteins
• Hydrolytic enzymes,
transport proteins
• Electron transport
proteins
• Proteins for ppd syn
• Modify toxic compd

30. COMPONENTS EXTERNAL TO CELL WALL
Capsule, Slime layer and S layer
Capsule- chemical structure-
1. Polysaccharide
2. Protein
3. Polysaccharide-Protein

31. GLYCOCALYX(capsule,slime)
• When the layer is well organized and not
easily washed out
• When it is a zone of diffuse, unorganized
material that is removed easily

33. Capsule under the microscope

34. Functions of Capsule
• Resist phagocytosis
• Storing water, prevents from
desiccation
• Helps in attachment

35. S layer
• External to cell wall

37. Functions of S layer
1. Protection against -
• ions and pH fluctuation
• Adverse surroundings
2. Maintains shape
3. Promotes adhesion
4. Adds the property of virulence

38. Pilus (pili, fimbriae)
• Short, fine, hair like appendages
• Visible under electron microscope
only
• One cell may have 1000 of pili
• Slender tube
• 3-10nm in diameter, several
micrometer in length

39. PILI

40. PILI

42. Pilus
Helically
arranged
pilin
proteins
Chemical
composition-
Protein- PILIN

43. Functions of Pili
• Attachment-rock surface, host cell
• Some may help in motility eg type IV-
jerky motility up to several mm
• Gliding motility eg. Myxobacteria
• conjugation

45. Flagella(flagellum)
• Thread like locomotory organelle
• Extending outward from the cw and pm
• Slender, rigid structure
• 20nm across and 15-20micrometer long
• Stained and can be seen under
compound ms
• Ultrastructure under electron ms

46. Arrangement of flagella

48. Ultrastructure of
flagella
Under TEM

50. Ultra structure of flagella

51. Flagellar ultrastructure
Three parts
1.Filament
2.Basal body
3.hook

52. Ribosome

53. Ribosomes
Location- cytoplasm and some attached to pm
complex structure
Composition- protein and ribonucleic acid
(RNA)
Parts- 50s and 30s(s- svedberg unit)
Function- protein synthesis
Folding of protein- by special protein called
chaperone

54. Ribosome contd.
Size- 14-15nm by 20nm
Mol wt.-2.7 million

55. The nucleoid

56. The most striking feature
no nuclear membrane
Located in an irregularly shaped
region called nucleoid
Other names
Nuclear body, chromatin, nuclear
region

57. Forms
1. Double stranded
DNA(deoxyribonucleic acid)
2. Linear chromosome
3. Some have more than one
chromosome

58. • A chromosome is a structure of DNA,
protein, and RNA found in cells.
• It is a single piece of coiled DNA containing
many genes, regulatory elements and other
nucleotide sequences.
• Chromosomes also contain DNA-bound
proteins, which serve to package the DNA
and control its functions.
• DNA encodes most or all of an organism's
genetic information;
• some species also contain plasmids or other
extra chromosomal genetic elements.

59. Electron micrograph

62. Chemical analysis
• 60% DNA
• 30% RNA
• 10% Protein
• E.coli-DNA circle-
1400µm
230-700 times longer than the cell
Looped and coiled efficiently
No histone protein

63. Exceptions- Perillulla & Gemmata
Gemmata

65. plasmid

66. Extra chromosomal DNA material

67. Plasmid
Examples- bacteria, fungi, yeast.
Small, double stranded DNA molecule
Exist independent of chromosome
Linear and circular
Few genes –less than 30
Not essential for survival
Selective advantage

68. Plasmid
Replicate autonomously
Single copy produces one copy per cell
Able to integrate into the chromosome
and gets replicated – episome
Sometimes lost
The loss of plasmid- curing

69. Curing agents
• UV and ionizing radiation
• Thymine starvation
• Antibiotics
• Growth above optimal
temperature

70. Types of Plasmids
type host function
Fertilty factor E.coli conjugation
Metabolic
plasmids
E.Coli
Rhizobium
Lactose
degradation&
symbiosis
Nitrogen fixation
R plasmid Pseudomonas Resistance to
antibiotic
Col plasmid E.coli Colicin
production
Virulence
plasmid
E.coli Entrotoxin,
siderophore

71. Cell membrane
• Retains cytoplasm
• Selective membrane
• Prevents loss of essential
components
• Transport system
• Waste excretion
• Protein secretion

72. Plasma membrane-functions
• Location for respiration, photosynthesis,
synthesis of lipid and cell wall
constituents
• Has receptor molecule to detect and
respond to chemicals in the surrounding
• Essential for the survival of bacteria

74. Fluid Mosaic Model

75. Fluid Mosaic Model of Singer &
Nicolson
• Bilayer phospholipid (amphipathic)
• Proteins float within
• 5-10 nm thickness
• Polar hydrophilic head
• Long non polar hydrophobic end
• Proteins-peripheral-20-30%,integral-60-80%
• No cholesterol but hopanoids

77. Internal membrane
Tubule ,vesicle,
lamellae
Cyanobacteria-infoldings
are complex
Spherical & flattened
vesicle, tubular
membranes

78. Inclusion structures
Carbon storage polymers
1. Poly-β-hydroxybutyric acid
1. PHB

79. Length:C3-C18

80. PHB
Synthesis when carbon is in excess
and used for biosynthesis and to make
ATP
PHB are referred to as poly-β-
hydoxyalkonate(PHA)
2. glycogen- polymer of glucose
Store house of carbon and energy

81. Polyphosphates

82. Polyphosphate contd
Functions- source of phosphate
Used as sources of phosphates for nucleic
acid and phospholipid biosynthesis
Note- phosphate in the environment is
limited

83. Sulfur Granules
Elemental sulfur accumulated inside the cell

84. Sulfur
• Oxidize reduced sulfur(H2S)

85. Magnetosomes

86. Magnetosomes
• Some bacteria can orient themselves within
magnetic field because of magnetosomes-
magnetotaxis
• These are intracellular particles
• Iron materials
• Impart magnetic dipole on a cell
Functions-not known
May be guiding bacteria towards magnetic field
deep in aquatic envt. Where oxygen level is low

87. Magnetosomes
• Surrounded by a membrane
containing phospholipid, proteins,
and glycoprotein
• Proteins act as chelating agents
• Square to rectangular in shape to
spike shaped

88. Gas vesicle
• Planktonic- those live in floating state
• Because of gas vesicles
• These structure confer buoyancy on cell
• Eg. Cyanobacteria also called
BGA(bloom)
• Purple and green sulfur bacteria
• Archaea
Note- Eucaryotes don’t have these
structure

89. bloom

90. bloom

93. General structure
• Spindle shaped filled with gas
• Made up of protein
• Hollow yet rigid
• Variable length and diameter
• 300nm-1000nm by 45nm-120nm
• Number-few to 100 per cell
• Membrane made up of protein, 2mm thick
• Impermeable to water and solute but
permeable to gas

94. Gas vesicle contd.
• Clusters of vesicles- gas vacuole
• Can be seen under light microscope and TEM

95. Molecular structure
• Major gas vesicle protein-GvpA- small,
hydrophobic and rigid(97%)
• Minor protein-GvpC

97. Other inclusion
• Cynophysin and granules- equal amount of
arginine and aspartic acid
• Store extra amount of nitrogen
Carboxysome present in photosynthetic bacteria
Polyhedral, 100nm in diameter, contains enzyme
ribulose 1, 5 biphosphate carboxylase(Rubisco)

98. Endospore

99. Endospore
• Endo-within
• Enable cells to endure difficult time-
Temperatures, drying, nutrient depletion
etc.
Dormant stage of bacteria-
Used for dispersal
Examples-Bacillus, Clostridium

101. Electron micrograph of endospore

102. Schematic presentation of endospore

103. Endospore formation and
germination
Activation- Use of elevated
temperature
Germination-Specific nutrient like
alanine
Outgrowth

111. Three stages
Activation- endospores get ready for
germination
Germination- rapid process, spore
loses its refractibility
Outgrowth-swelling due water up
take, synthesis of new RNA, proteins
&DNA.

112. characteristics
• Dipicolinic acid in core (with calcium)in
core (10%)- reduces the water content
of core.
• Endospores become dehydrated
1. Increases heat resistance
2. Makes cells resistant to chemicals
3. Keeping enzymes inactive in the core

113. characteristics
• pH one unit lower than vegetative cell
• High level of SASPs(small acid soluble
proteins)
1. Bind tightly to DNA in the core –protection
from UV, desiccation, and dry heat
(DNA changed from B form to the compact
form A which is more resistant to mutation,
denaturing effect of dry heat)
2. Carbon and energy source

114. Difference between vegetative cell &
endospore
Vegetative cell Endospore