Morphology of Bacterial Cell

1. Morphology of bacteria
Course: B.Sc. Microbiology
Sem II
Sub: Bacteriology
Unit II

2. • In microbiology, the term morphology means
cell shape. Several morphologies are known
among prokaryotes.

3. The basic morphology of a cell
1

4. 1. The Cell Membrane
• Phospholipid bilayer: 2 surface layers of hydrophilic
of polar head and inner layer of hydrophobic
nonpolar tail.
• Peripheral proteins: Function as enzyme scaffold for
support and mediator for cell movement
• Integral proteins: disrupting lipid bilayer. Other types
known as transmembrane protein
• Glycoprotein: protein attached to the carbohydrate
• Glycolipid: Lipid attached to carbohydrate

5. Membrane structureFluid mosaic model
2

6. Characteristics of Lipid bilayer
• Semi-permeable
• Consists of : 1) hydrophilic
2) hydrophobic
• Main function is to:
– Protect cell (as outercovering)
– Keep the things that are on the
inside of a cell inside, and keep
what things are outside the cell
on the outside.
– It allows some things, under
certain situations, to cross the
phospholipid bilayer to enter or
exit the cell.
3

7. Function of the Cell Membrane
• Protective outer covering for the cell.
• Cell membrane anchors the cytoskeleton (a cellular 'skeleton' made of
protein and contained in the cytoplasm) and gives shape to the cell.
• Responsible for attaching the cell to the extracellular matrix (non living
material that is found outside the cells), so that the cells group together to
form tissues.
• Transportation of materials needed for the functioning of the cell
organelles without using cellular energy.
• The protein molecules in the cell membrane receive signals from other
cells or the outside environment and convert the signals to messages, that
are passed to the organelles inside the cell.
• In some cells, the protein molecules in the cell membrane group together
to form enzymes, which carry out metabolic reactions near the inner
surface of the cell membrane.
• The proteins help very small molecules to get transported thru cell
membrane, provided, the molecules are traveling from a region with lots
of molecules to a region with less number of molecules.

8. The cell membrane
• Lies between two
dark line
• Prokaryote have less
sterol as compared to
the eukaryote,
causing rigid structure
• Less-sterol wall in
prokaryote is
Mycoplasma
Lipid bilayer of plasma
membrane
Taken with TEM
4

9. 2. The bacterial cell wall
• Has peptidoglycan
• Marks the difference between gram
+ve and gram –ve bacteria

10. Peptidoglycan
• Polymer of disaccharide
• Also known as murein,
• is a polymer consisting of sugars
and amino acids that forms a
mesh-like layer outside the
plasma membrane of bacteria
(but not Archaea), forming the
cell wall.
• The sugar component consists of
alternating residues of N-
acetylglucosamine (NAG) and N-
acetylmuramic acid (NAM).
• Attached to the N-acetylmuramic
acid is a peptide chain of three to
five amino acids.
5

11. 3. Cell wall of Gram negative and positive
Gram negative Gram positive
Thin peptidoglycan Thick peptidoglycan
Has outer membrane Teichoic acid
Periplasmic space
Tetracycline sensitive Penicillin sensitive
4 ring basal body 2-ring basal body
Disrupted by lysozyme Disrupted by endotoxin

12. Gram positive and Gram negative
6

13. A, Gram positive bacterium thick
peptidoglycan layer contains
teichoic and lipoteichoic acids.
B, Gram negative bacterium thin
peptidoglycan layer and an outer
membrane that contains
lipopolysaccharide, phospholipids,
and proteins. The periplasmic
space between the cytoplasmic
and outer membranes contains
transport, degradative, and cell
wall synthetic proteins. The outer
membrane is joined to the
cytoplasmic membrane at
adhesion points and is attached to
the peptidoglycan by lipoprotein
links.
Gram positive and Gram negative bacterial cell walls
7

14. Peptidoglycan in Gram positive bacteria
• Linked by polypeptides
8

15. Gram positive bacterial cell wall
• Teichoic acid
- Lipoteichoic acid links to plasma membrane
- Wall teichoic acid links to peptidoglycan
• May regulate movement of cations
• Polysaccharides provide antigenic variation

16. Gram negative bacteria outer membrane
• Lipopolysacharides, lipoproteins, phospholipids
• Forms the periplasm between the outer
membrane and the plasma membrane
• Protection from phagocytes, complement and
antibiotics
• O-polysaccharide antigen e.g. E. coli O157:H7
• Lipid A is an endotoxin
• Porins (proteins) form channel through
membrane

17. The Gram stain Mechanism
• Crystal violet-iodine crystals form in cell
• Gram positive
- Alcohol dehydrates peptidoglycan
- CV-I crystals do not leave
• Gram negative
- Wall is lesser or
- Wall is made up of pseudomurein (lack NAM
and D-amino acids)

18. Acid-fast organisms are difficult to characterize
using standard microbiological techniques (e.g.
Gram stain - if you gram stained an AFB the result
would be an abnormal gram positive organism,
which would indicate further testing), though they
can be stained using concentrated dyes, particularly
when the staining process is combined with heat.
Once stained, these organisms resist the dilute acid
and/or ethanol-based de-colorization procedures
common in many staining protocols—hence the
name acid-fast.

19. Atypical Cell Wall
• Acid-fast cell wall
- e.g gram positive
- Waxy lipid (mycolic acid) bound to
peptidoglycan
- Mycobacterium
- Nocardia

20. Atypical Cell Wall
• Mycoplasmas
- Lack cell walls
- Sterols in plasma membrane
• Archaea
-Wall-less or Wallas of pseudomurein (lack
Nam and D-amino acids)

21. Cell Wall-less Forms
• Few bacteria are able to live or exist without a cell wall.
• The mycoplasmas are a group of bacteria that lack cell wall.
• Mycoplasmas have sterol-like molecules incorporated into their
membranes and they are usually inhabitants of osmotically-
protected environments.
• Mycoplasma pneumoniae is the cause of primary atypical bacterial
pneumonia, known in the vernacular as "walking pneumonia". For
obvious reasons, penicillin is ineffective in treatment of this type of
pneumonia. Sometimes, under the pressure of antibiotic therapy,
pathogenic streptococci can revert to cell wall-less forms (called
spheroplasts) and persist or survive in osmotically-protected
tissues. When the antibiotic is withdrawn from therapy the
organisms may regrow their cell walls and reinfect unprotected
tissues.

22. Damage to the cell wall
• (Gram –ve): Lysozyme digests disaccharide in
peptidoglycan
• (Gram +ve): Penicillin inhibits peptide bridges in
peptidoglycan
• Protoplast is a wall-less cell
• Spheroplast is a wall-less gram positive cell
- Protoplasts and spheroplasts are susceptible to osmotic lysis
• L forms are wall-less cells that swell into irregular
shapes

23. External structures
• Many bacteria have structures that extend
beyond or surround cell wall
I. Flagella and pili extend from the cell
membrane through the cell wall and beyond
II. Capsules and slime layers surround the cell
wall

24. 4. Bacterial Cell Surface Structures
• Arrangements of Bacterial Flagella
1. Monotrichous: Bacteria with a single flagellum
located at one end (pole)
2. Amphitrichous: Bacteria with 2 flagella one at
each end
3. Peritrichous: Bacteria with flagella all over the
surface
4. Atrichous: Bacteria without flagella
5. Cocci shaped bacteria rarely have flagella

25. Structure of flagella in gram –ve and +ve bacteria
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26. Chemotaxis
• Bacteria move away or towards subtances that
are present in the environment through a
nonrandom process
1. Positive chemotaxis: movement towards
attractants (nutrients)
2. Negative chemotaxis: movement away from
the repellent

27. Pili
• Pilus (singular)
• Tiny hollow projections
• Used to attach bacteria to surfaces
• Not involved in movement
1. Long conjugation
2. Short attachment pili (fimbriae)

28. Glycocalyx
• Capsule & Slime Layer
• Used to refer to all
polysaccharide/polypeptide containing
substances found external to cell wall
1. Capsule
2. Slime layers
3. All bacteria at least have thin small layer

29. 5. Glycocalyx
Capsule
• More firmly attached to the cell wall.
• Have a gummy, sticky consistency and
provide protection & adhesion to solid
surfaces and to nutrients in the
environment.
• Bacteria that possess capsules are
considered encapsulated, and generally
have greater pathogenicity because
capsules protect bacteria, even from
phagocytic white blood cells of the
immune system.
• The adhesive power of capsules is also
a major factor in the initiation of some
bacterial diseases.
Slime Layer
• A glycocalyx is considered a
slime layer when the
glycoprotein molecules are
loosely associated with the
cell wall. Bacteria that are
covered with this loose
shield are protected from
dehydration and loss of
nutrients.

30. Capsule
• Protective structure outside the cell wall of
the organism that secretes it
• Only certain bacteria are capable of forming
capsules
• Chemical composition of each capsule is
unique to the strain of bacteria that secrete it
• Encapsulated bacteria are able to evade host
defense mechanism (phagocytosis)

31. Slime Layer
• Less tightly bound to the cell wall and is
usually thinner than the capsule
• Protects the cell against drying, traps nutrients
and binds cells together (biofilms)

32. Biofilms
• Biofilm usually begins
to form when free
swimming bacterium
attaches to a surface
• Share nutrients
• Shelter from harmful
factors 10

33. Case Study
• Patients with indwelling catheters received
contaminated heparin with Pseudomonas
fluorescens
• Bacterial numbers in contaminated heparin
were too low to cause infection
• 84–421 days after exposure, patients
developed infections
Delayed Bloodstream Infection Following
Catheterization

34. Functions Of The Bacterial Envelope
Function Component(s)
Structural Rigidity All.
Packaging Of Internal Contents All.
Permeability Barrier
Outer membrane or plasma
membrane.
Metabolic Uptake
Membranes and periplasmic
transport
proteins, porins, permeases.
Energy Production Plasma membrane.
Adhesion To Host Cells Pili, proteins, teichoic acid.
Immune Recognition By Host All outer structures.
Escape From Host Recognition Capsule, M protein.
Antibiotic Sensitivity Peptidoglycan synthetic enzymes.
Antibiotic Resistance Outer membrane.
Motility Flagella.
Mating Pili.
Adhesion Pili.

35. References
Books:
Biology of microorganisms By M. T. Madigan, J. M. Martinko, D. A. Stahl and D. P. Clark
Images:
1. http://3.bp.blogspot.com/_BwlbMaa50jo/TI1aRa_uoPI/AAAAAAAAHZI/CRr9tao2htE/s160
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2. http://125.218.212.107/fzswx/Upload//Y8UZ2UzYpf2TUAsf79s3JziWKhYR1U0R.jpg
3. https://lh5.ggpht.com/vPiDZmR3fJkVXku8jPP8KHdOOiPaTSDsWHzEOE4sn1WWC_2DhHIp
-Ps86Wk7_cLjpiBqdg=s89
4. http://en.wikipedia.org/wiki/History_of_cell_membrane_theory#mediaviewer/File:Annul
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5. https://www.flickr.com/photos/ajc1/2281351707/
6. http://2.bp.blogspot.com/_YU9DUZHbrgg/S5piaVtozzI/AAAAAAAAARg/vEiF3Rlr0CI/s320/
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7. https://lh5.ggpht.com/GExUjsnrmU1GghQWct5gB8jT2nvFaE70QXoHmxNJ7gh1bOOQsnh
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8. http://classes.midlandstech.edu/carterp/Courses/bio225/chap04/ss4.htm
9. https://lh5.ggpht.com/JXrtEDW7_IVYJAA2szt0wKEtn2D2aiZB9MTfiSszOobnsFzRqUM2qiV
E5jH9QeEouxOewA=s159
10. http://www.drchetan.com/dentalpics/plog-content/thumbs/dental-pics/dental-
plaque/small/124-dental-plaque-microscopy.jpg