Morphology & Cell Biology of
Bacteria
Siti Sarah Jumali (ext 2123)
Room 3/14
sarah_jumali84@hotmail.com
The basic morphology of a cell
the
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
Membrane structure
Fluid mosaic model
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.
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.
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
2. The bacterial cell wall
• Has peptidoglycan
• Marks the difference between gram
+ve and gram –ve bacteria
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 Nacetylglucosamine (NAG) and Nacetylmuramic acid (NAM).
• Attached to the N-acetylmuramic
acid is a peptide chain of three to
five amino acids.
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
Gram positive and Gram negative
Gram positive and Gram negative bacterial cell walls
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.
Peptidoglycan in Gram positive bacteria
• Linked by polypeptides
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
Gram negative bacterial cell walls
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
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)
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.
Atypical Cell Wall
• Acid-fast cell wall
- e.g gram positive
- Waxy lipid (mycolic acid) bound to
peptidoglycan
- Mycobacterium
- Nocardia
Atypical Cell Wall
• Mycoplasmas
- Lack cell walls
- Sterols in plasma membrane
• Archaea
-Wall-less or Wallas of pseudomurein (lack
Nam and D-amino acids)
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 osmoticallyprotected 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.
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
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
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
Polar Monotrichous flagellum
Vibriocholerae
Amphitrichous flagella arrangement
Spirillum
Lophotrichous flagella arrangement
Spirillum
Structure of flagella in gram –ve and +ve bacteria
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
Chemotaxis
Chemotaxis
Pili
• Pilus (singular)
• Tiny hollow projections
• Used to attach bacteria to surfaces
• Not involved in movement
1. Long conjugation
2. Short attachment pili (fimbriae)
E. coli (14,300X)
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
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.
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)
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)
Biofilms
• A microbial community that usually forms slimy layer
or hydrogel on a surface
• Bacteria attracted by chemicals via quorum sensing
• Composed of populations or communities of
microorganisms adhering to environmental surfaces.
• The microorganisms are usually encased in
extracellular polysaccharide that they synthesize.
• Can be found in sufficient moisture is present.
• Their development is most rapid in flowing systems
where adequate nutrients are available
Biofilms
• Biofilm usually begins
to form when free
swimming bacterium
attaches to a surface
• Share nutrients
• Shelter from harmful
factors
Thoughts for the day..
• What is the biofilm that forms on teeth called?
Case Study
Delayed Bloodstream Infection Following
Catheterization
• 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
Questions?
Functions Of The Bacterial Envelope
Function
Structural Rigidity
Packaging Of Internal Contents
Permeability Barrier
Metabolic Uptake
Energy Production
Adhesion To Host Cells
Component(s)
All.
All.
Outer membrane or plasma
membrane.
Membranes and periplasmic
transport
proteins, porins, permeases.
Plasma membrane.
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
Motility
Mating
Adhesion
Outer membrane.
Flagella.
Pili.
Pili.