introduction Microbial cell biology .pdf
aeidmicrobiology
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Oct 13, 2024
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About This Presentation
introduction to microbial cell
Slide Content
Microbial cell Biology
By
Dr/ Ahmed Eid Mohamed
Lecturer of applied microbiology
By
Dr/ Ahmed Eid Mohamed
Lecturer of applied microbiology
The importance of structure to understanding microbes
•Learning structures helps in understanding functions;
Pathogens having structures to enhance their ability to cause illness
Pili: helps microbes to attach to victims
F-pilus: during mating, exchange of genetic information through F-pilus
Movement: through solutions, detects favorable and unfavorable conditions by flagella, gliding motility
As microbes grows, it proliferate, knowing what is made of and how it is assemblage for
understanding the growth process
Survival insurance; rest structures as; carbon, nitrogen, sulfur or phosphorus in inclusions allow
microbes to sleep during bad times
•Learning structures helps in understanding functions;
Pathogens having structures to enhance their ability to cause illness
Pili: helps microbes to attach to victims
F-pilus: during mating, exchange of genetic information through F-pilus
Movement: through solutions, detects favorable and unfavorable conditions by flagella, gliding motility
As microbes grows, it proliferate, knowing what is made of and how it is assemblage for
understanding the growth process
Survival insurance; rest structures as; carbon, nitrogen, sulfur or phosphorus in inclusions allow
microbes to sleep during bad times
Eukaryotic Vs prokaryotic cells
Eukaryotic cell Prokaryotic cell
1- Nuclear body a- Bounded by a nuclear membrane
b- Contains one or more paired,
linear chromosomes, associated with
histone
c- Nucleolus present
d- Nuclear body called Nucleus
a- Not bound by a nuclear membrane
b- one circular chromosome,
associated with histone-like proteins
c- No Nucleolus
d- Nuclear body called Nucleoid
2- Cell division a- Mitosis (vegetative)
b- Meiosis (diploid sex cells)
a- Binary fission
b- No mitosis
c- No meiosis (organisms are haploid)
3- Cytoplasmic
membrane
Fluid phospholipid bilayer,
containing sterols and carbohydrates
Fluid phospholipid bilayer, usually
lacking sterols, no carbohydrates
Many bacteria contain hopanoids
Eukaryotic cell Prokaryotic cell
1- Nuclear body a- Bounded by a nuclear membrane
b- Contains one or more paired,
linear chromosomes, associated with
histone
c- Nucleolus present
d- Nuclear body called Nucleus
a- Not bound by a nuclear membrane
b- one circular chromosome,
associated with histone-like proteins
c- No Nucleolus
d- Nuclear body called Nucleoid
2- Cell division a- Mitosis (vegetative)
b- Meiosis (diploid sex cells)
a- Binary fission
b- No mitosis
c- No meiosis (organisms are haploid)
3- Cytoplasmic
membrane
Fluid phospholipid bilayer,
containing sterols and carbohydrates
Fluid phospholipid bilayer, usually
lacking sterols, no carbohydrates
Many bacteria contain hopanoids
Eukaryotic cell Prokaryotic cell
4- Endocytosis Capable of endocytosis and
exocytosis
incapable of endocytosis and
exocytosis
5- Cytoplasmic
structures
a- Ribosomes 80 S (60 S, 40 S
subunits)
b- Internal membrane bound
organelles as; endoplasmic
reticulum, Golgi apparatus,
vacuoles and lysosomes are present
c- Chloroplasts
d- Cytoskeleton
e- Mitotic spindle (involved in
mitosis)
a- Ribosomes 70 S (50 S, 30 S)
b- Membrane bound organelles are
absent
c- No chloroplasts
d- No cytoskeleton
e- No mitotic spindle
6- Respiratory
enzymes and electron
transport chain
Located in the mitochondria Located in the cytoplasmic membrane
4- Endocytosis Capable of endocytosis and
exocytosis
incapable of endocytosis and
exocytosis
5- Cytoplasmic
structures
a- Ribosomes 80 S (60 S, 40 S
subunits)
b- Internal membrane bound
organelles as; endoplasmic
reticulum, Golgi apparatus,
vacuoles and lysosomes are present
c- Chloroplasts
d- Cytoskeleton
e- Mitotic spindle (involved in
mitosis)
a- Ribosomes 70 S (50 S, 30 S)
b- Membrane bound organelles are
absent
c- No chloroplasts
d- No cytoskeleton
e- No mitotic spindle
6- Respiratory
enzymes and electron
transport chain
Located in the mitochondria Located in the cytoplasmic membrane
Eukaryotic cell Prokaryotic cell
7- Cell wall a- plant cells, algae and fungi have
cell walls (cellulose or chitin), No
peptidoglycan
b- Animal cells and protozoans lack
cell walls
a- Eubacterial cell wall
(peptidoglycan)
b- Archaebacterial cell wall (protein,
complex carbohydrate or unique
molecules resembling peptidoglycan)
8- Locomotor
organelles
May have flagella or cilia (sliding
microtubules surrounded by a
membrane , 2x9 + 2)
No cilia
Flagella (single rotating fibril, not
surrounded by a membrane)
9- Representative
organisms
Animals, plants, algae, protozoans
and fungi
Bacteria (eubacteria and
archaebacteria)
7- Cell wall a- plant cells, algae and fungi have
cell walls (cellulose or chitin), No
peptidoglycan
b- Animal cells and protozoans lack
cell walls
a- Eubacterial cell wall
(peptidoglycan)
b- Archaebacterial cell wall (protein,
complex carbohydrate or unique
molecules resembling peptidoglycan)
8- Locomotor
organelles
May have flagella or cilia (sliding
microtubules surrounded by a
membrane , 2x9 + 2)
No cilia
Flagella (single rotating fibril, not
surrounded by a membrane)
9- Representative
organisms
Animals, plants, algae, protozoans
and fungi
Bacteria (eubacteria and
archaebacteria)
Typical prokaryotic cell
Summary of bacterial cell structures
Structure Function(s) Predominant chemical composition
Flagella Swimming movement Protein
Pili; a- Sex pilus Mediates DNA transfer during
conjugation
Protein
b- common pili
(fimbriae)
Attachment to surfaces & protection Protein against phagotrophic
engulfment
Capsules (slime layer
& glycocalyx)
Attachment to surfaces
Protection against phagocytosis,
killing, digestion and desiccation
Reserve of nutrients
Polysaccharide & possible polypeptide
Structure Function(s) Predominant chemical composition
Flagella Swimming movement Protein
Pili; a- Sex pilus Mediates DNA transfer during
conjugation
Protein
b- common pili
(fimbriae)
Attachment to surfaces & protection Protein against phagotrophic
engulfment
Capsules (slime layer
& glycocalyx)
Attachment to surfaces
Protection against phagocytosis,
killing, digestion and desiccation
Reserve of nutrients
Polysaccharide & possible polypeptide
Structure Function(s) Predominant chemical composition
Cell wall
Gram-positive
Peptidoglycan prevents osmotic lysis
and confers rigidity and shape
Outer membrane; permeability
barrier, LPS & proteins have
various functions
Peptidoglycan (murein) complexed with
teichoic acids
Gram-negative Peptidoglycan (murein) and outer
membrane (phospholipid, protein and
lipopolysaccharide)
Plasma membrane Permeability barrier, transport of
solutes
Energy generation, location of
various enzymes
Phospholipid and protein
Ribosomes Protein synthesis, translation RNA and protein
Inclusions Reserves of nutrients Highly variable; carbohydrate, lipid,
protein or inorganic
chromosome Genetic material DNA
plasmid Extrachromosomal genetic material DNA
Cell wall
Gram-positive
Peptidoglycan prevents osmotic lysis
and confers rigidity and shape
Outer membrane; permeability
barrier, LPS & proteins have
various functions
Peptidoglycan (murein) complexed with
teichoic acids
Gram-negative Peptidoglycan (murein) and outer
membrane (phospholipid, protein and
lipopolysaccharide)
Plasma membrane Permeability barrier, transport of
solutes
Energy generation, location of
various enzymes
Phospholipid and protein
Ribosomes Protein synthesis, translation RNA and protein
Inclusions Reserves of nutrients Highly variable; carbohydrate, lipid,
protein or inorganic
chromosome Genetic material DNA
plasmid Extrachromosomal genetic material DNA
The Cytoplasmic membrane
•It is the most conserved structure in living cells, immediately surrounding the cytoplasm.
•Membranes are thin structures (7-8 nm), they are the major barrier in the cell, separating the inside of
the cell from the outside and found in every living thing.
•Allow cells to selectively interact with their environment
•Membranes are a symmetric, dynamic and constantly adapting to changing environmental conditions
•Composed of a fluid phospholipid bilayer imbedded with protein
•Prokaryotic membranes lack sterols
•Many bacteria contain hopanoids (sterol-like molecules)
•It is the most conserved structure in living cells, immediately surrounding the cytoplasm.
•Membranes are thin structures (7-8 nm), they are the major barrier in the cell, separating the inside of
the cell from the outside and found in every living thing.
•Allow cells to selectively interact with their environment
•Membranes are a symmetric, dynamic and constantly adapting to changing environmental conditions
•Composed of a fluid phospholipid bilayer imbedded with protein
•Prokaryotic membranes lack sterols
•Many bacteria contain hopanoids (sterol-like molecules)
Cytoplasmic
membrane
membrane
•Polar ends composed of
phosphate and glycerol
(water soluble/ hydrophilic)
•Non polar ends composed of
Fatty acid
(insoluble in water/ hydrophobic)
phosphate and glycerol
(water soluble/ hydrophilic)
•Non polar ends composed of
Fatty acid
(insoluble in water/ hydrophobic)
•20-30 % of membrane associated
protein is soluble in water and
loosely associated
•70-80 % is tightly bound to the
membrane , often spanning both
sides
•These proteins are often
amphipathic molecules with
stretches of hydrophilic amino
acids and stretches of
hydrophobic amino acids
protein is soluble in water and
loosely associated
•70-80 % is tightly bound to the
membrane , often spanning both
sides
•These proteins are often
amphipathic molecules with
stretches of hydrophilic amino
acids and stretches of
hydrophobic amino acids
Bilayer formation
•Phospholipid molecule is amphipathic
•In aqueous environment it forms the
lipid bilayer (very stable form, called
membrane vesicles)
•Selective permeability;
small non -polar (O
2, Co
2)
small polar (H
2O, ethanol)
Large non- polar (Benzene)
Large polar (Glucose)
Charged as ions (Cl
-
, Na
+
), amino
acids “ incredibly polar”
•Phospholipid molecule is amphipathic
•In aqueous environment it forms the
lipid bilayer (very stable form, called
membrane vesicles)
•Selective permeability;
small non -polar (O
2, Co
2)
small polar (H
2O, ethanol)
Large non- polar (Benzene)
Large polar (Glucose)
Charged as ions (Cl
-
, Na
+
), amino
acids “ incredibly polar”
Properties of the Bacteria and Eukarya
Cell Membranes
•Their cell membrane is composed of a phospholipid bilayer.
•Their phospholipids are composed of a hydrophillic phosphate head
group and 2 lipid tails that are hydrophobic.
•The tails are unbranched fatty acids (made up of hydrocarbons H-
C)
•The phosphate head group is attached to the fatty acid tail via an
ESTER BOND.
Cell Membranes
•Their cell membrane is composed of a phospholipid bilayer.
•Their phospholipids are composed of a hydrophillic phosphate head
group and 2 lipid tails that are hydrophobic.
•The tails are unbranched fatty acids (made up of hydrocarbons H-
C)
•The phosphate head group is attached to the fatty acid tail via an
ESTER BOND.
Stabilization of the membrane
•The cytoplasmic membrane is stabilized by hydrophobic interactions between neighboring lipids
•And by hydrogen bonds between neighboring lipids & hydrogen bonds between membrane
proteins and lipids
•Further stability come from negative charges on proteins that form ionic interactions with divalent
cations such as Mg
+2
and Ca
+2
and the hydrophilic head of lipids
•The cytoplasmic membrane is stabilized by hydrophobic interactions between neighboring lipids
•And by hydrogen bonds between neighboring lipids & hydrogen bonds between membrane
proteins and lipids
•Further stability come from negative charges on proteins that form ionic interactions with divalent
cations such as Mg
+2
and Ca
+2
and the hydrophilic head of lipids
Functions of the cell membrane
* Retains the cytoplasm;
solutes (ions, sugars) concentration are much higher within the cell than outside.
solutes tends to equilibrate, causing water to flow into the cell (Osmosis) and solutes flow out
Retain various chemicals needed for metabolism
•Selective barrier;
Cell membrane is able to accommodate entry of nutrients and exit of waste
Some molecules can cross the membrane without assistance, most cannot
Non polar molecules penetrate by actually dissolving into the lipid bilayer
Molecules less than 0.8 nm in diameter
* Retains the cytoplasm;
solutes (ions, sugars) concentration are much higher within the cell than outside.
solutes tends to equilibrate, causing water to flow into the cell (Osmosis) and solutes flow out
Retain various chemicals needed for metabolism
•Selective barrier;
Cell membrane is able to accommodate entry of nutrients and exit of waste
Some molecules can cross the membrane without assistance, most cannot
Non polar molecules penetrate by actually dissolving into the lipid bilayer
Molecules less than 0.8 nm in diameter
small non polar (O
2, Co
2) Fast and easy
small polar (H
2O, ethanol) Slowly
Large non polar (Benzene) Slowly
Large polar (Glucose) No entry
Charged as ions (Cl-, Na+), amino acids “ incredibly polar” No entry
Most polar compounds such as amino acids, organic acids and inorganic salts are not
allowed entry and must be transported across the membrane by proteins or carrier molecules
2, Co
2) Fast and easy
small polar (H
2O, ethanol) Slowly
Large non polar (Benzene) Slowly
Large polar (Glucose) No entry
Charged as ions (Cl-, Na+), amino acids “ incredibly polar” No entry
Most polar compounds such as amino acids, organic acids and inorganic salts are not
allowed entry and must be transported across the membrane by proteins or carrier molecules
Simple diffusion
•The net movement of small molecules or ions down their concentration gradient (Random, no energy)
until equilibrium
•Molecules and atoms possess kinetic energy, if not evenly distributed on both sides of a membrane,
the difference in their concentration concentration gradient potential energy
•Diffusion is powered by the potential energy of a concentration gradient (no metabolic energy)
•EX; transport of O
2 and CO
2 into in and out of cells
•Transport rate depends on; permeability of the membrane (organization of membrane lipid and protein)
•The net movement of small molecules or ions down their concentration gradient (Random, no energy)
until equilibrium
•Molecules and atoms possess kinetic energy, if not evenly distributed on both sides of a membrane,
the difference in their concentration concentration gradient potential energy
•Diffusion is powered by the potential energy of a concentration gradient (no metabolic energy)
•EX; transport of O
2 and CO
2 into in and out of cells
•Transport rate depends on; permeability of the membrane (organization of membrane lipid and protein)
Simple diffusion
Osmosis
•the diffusion of solvent (water) across a membrane from an area of higher water conc (lower solute conc)
to lower water conc (higher solute conc)
•Powered by the potential energy of a concentration energy, do not need expenditure of metabolic energy
•When a solute (sugar) dissolves in water, it forms weak hydrogen bonds with water molecules. While
free unbound water molecules are small enough to pass through membrane pores, water molecules
bound to solute are not
•So, the higher the solute conc, the lower the conc of free water molecules capable of passing through the
membrane
•the diffusion of solvent (water) across a membrane from an area of higher water conc (lower solute conc)
to lower water conc (higher solute conc)
•Powered by the potential energy of a concentration energy, do not need expenditure of metabolic energy
•When a solute (sugar) dissolves in water, it forms weak hydrogen bonds with water molecules. While
free unbound water molecules are small enough to pass through membrane pores, water molecules
bound to solute are not
•So, the higher the solute conc, the lower the conc of free water molecules capable of passing through the
membrane
•A cell can find itself in one of three environments;
•Isotonic; both the water and solute conc are the same inside and outside the cell,
water goes into and out of cell equally
•Hypertonic; water conc is greater inside the cell, solute conc is greater outside the cell
water goes out of the cell
•Hypotonic; water conc is greater outside the cell, solute conc is higher inside the cell
water goes into the cell
•Isotonic; both the water and solute conc are the same inside and outside the cell,
water goes into and out of cell equally
•Hypertonic; water conc is greater inside the cell, solute conc is greater outside the cell
water goes out of the cell
•Hypotonic; water conc is greater outside the cell, solute conc is higher inside the cell
water goes into the cell
Isotonic,
hypertonic
and
hypotonic
environment
hypertonic
and
hypotonic
environment
Diffusion of polar molecules or ions
(metabolic needs solutes) by
a protein transporter
•Types of transporter proteins:
•Channel protein
simple; solutes moves down conc
gradient
gated; opened by a chemical or
electrical stimuli (different charges)
•Carrier protein
Transport specific solutes
(metabolic needs solutes) by
a protein transporter
•Types of transporter proteins:
•Channel protein
simple; solutes moves down conc
gradient
gated; opened by a chemical or
electrical stimuli (different charges)
•Carrier protein
Transport specific solutes
Gated channel protein Channel (simple) and carrier
protein
protein
Basic types of transporter proteins
•Uniporter;
A single substance, moves in a single direction (down a concentration gradient)
powered by potential energy of concentration gradient (passive transport)
•Antiporter;
Two substances, moves in opposite directions simultaneously
powered by ATP or proton motive force (active transport)
•Symporter;
Two substances, moves in the same direction simultaneously
powered by ATP or proton motive force (active transport)
•Uniporter;
A single substance, moves in a single direction (down a concentration gradient)
powered by potential energy of concentration gradient (passive transport)
•Antiporter;
Two substances, moves in opposite directions simultaneously
powered by ATP or proton motive force (active transport)
•Symporter;
Two substances, moves in the same direction simultaneously
powered by ATP or proton motive force (active transport)
Basic types of transporter proteins
Active transport
•Cell uses carrier proteins as; antiporters or symporters and energy to transport substances across the
membrane against the concentration or electrochemical gradient;
Active transport mechanisms can be;
* primary active transport
uses a source of chemical energy e.g. ATP
or from Proton motive force (PMF) (usually involves a symporter)
* secondary active transport
uses an electrochemical gradient – generated by active transport – as an energy source to
move molecules against their gradient, and thus does not directly require a chemical source of
energy such as ATP.
•Cell uses carrier proteins as; antiporters or symporters and energy to transport substances across the
membrane against the concentration or electrochemical gradient;
Active transport mechanisms can be;
* primary active transport
uses a source of chemical energy e.g. ATP
or from Proton motive force (PMF) (usually involves a symporter)
* secondary active transport
uses an electrochemical gradient – generated by active transport – as an energy source to
move molecules against their gradient, and thus does not directly require a chemical source of
energy such as ATP.
Active transport
PMF dependent
•Powered by proton motive
force
(movement of protons across
membrane)
•Involves a symporter
transport protons (H
+
) and
a substrate
PMF dependent
•Powered by proton motive
force
(movement of protons across
membrane)
•Involves a symporter
transport protons (H
+
) and
a substrate
•Powered by hydrolysis of
ATP
•Involves membrane
spanning transporter
•Specific periplasmic
binding protein carrier
Active transport
ATP-dependent
ATP
•Involves membrane
spanning transporter
•Specific periplasmic
binding protein carrier
Active transport
ATP-dependent
ABC system
Examples of active
transport include
transport of certain
sugars and amino
acids
Examples of active
transport include
transport of certain
sugars and amino
acids
Secondary active
transport
The electrochemical gradients set
up by primary active transport store
energy, which can be released as the
ions move back down their
gradients.
Secondary active transport uses the
energy stored in these gradients to
move other substances against their
own gradients.
transport
The electrochemical gradients set
up by primary active transport store
energy, which can be released as the
ions move back down their
gradients.
Secondary active transport uses the
energy stored in these gradients to
move other substances against their
own gradients.
Secondary active transport
•Ex, let's suppose we have a high concentration of sodium ions in the extracellular space (sodium-potassium
pump). If a route such as a channel or carrier protein is open, sodium ions will move down their
concentration gradient and return to the interior of the cell.
•the movement of the sodium ions down their gradient is coupled to the uphill transport of other substances
( ex; glucose) by a shared carrier protein (a cotransporter)
•a carrier protein lets sodium ions move down their gradient, but simultaneously brings a glucose molecule
up its gradient and into the cell. The carrier protein uses the energy of the sodium gradient to drive the
transport of glucose molecules.
•Ex, let's suppose we have a high concentration of sodium ions in the extracellular space (sodium-potassium
pump). If a route such as a channel or carrier protein is open, sodium ions will move down their
concentration gradient and return to the interior of the cell.
•the movement of the sodium ions down their gradient is coupled to the uphill transport of other substances
( ex; glucose) by a shared carrier protein (a cotransporter)
•a carrier protein lets sodium ions move down their gradient, but simultaneously brings a glucose molecule
up its gradient and into the cell. The carrier protein uses the energy of the sodium gradient to drive the
transport of glucose molecules.
Active transport; Group translocation
•A substance is chemically altered during its transport across a membrane so that once inside, the
cytoplasmic membrane becomes impermeable to that substance and it remains within the cell.
•Ex; Phosphotransferase system (in bacteria).
A high energy phosphate group from phosphoenolpyruvate (PEP) is transferred by a series of
enzymes to Glucose
The final enzyme both phosphorylates the Glucose and transports it across the membrane as
glucose-6-phosphate
•A substance is chemically altered during its transport across a membrane so that once inside, the
cytoplasmic membrane becomes impermeable to that substance and it remains within the cell.
•Ex; Phosphotransferase system (in bacteria).
A high energy phosphate group from phosphoenolpyruvate (PEP) is transferred by a series of
enzymes to Glucose
The final enzyme both phosphorylates the Glucose and transports it across the membrane as
glucose-6-phosphate
Group translocation
Comparison of transport systems
Property Passive diffusion Facilitated diffusion Active transport Group
translocation
Carrier
Mediated
_ + + +
Against
Concentration
Gradient
_ _ + Not Applicable
Specifity _ + + +
Energy expended _ _ + +
Solute modified
During transport
_ _ _ +
Property Passive diffusion Facilitated diffusion Active transport Group
translocation
Carrier
Mediated
_ + + +
Against
Concentration
Gradient
_ _ + Not Applicable
Specifity _ + + +
Energy expended _ _ + +
Solute modified
During transport
_ _ _ +
Mesosomes
•Found in both G+ , G -
•Infoldings of the bacterial cytoplasmic membrane seen as spherical structure
•Their function is not precisely known
(previously thought to be artifacts during preparing bacterial specimens for electron microscopy)
•Often found near septa or dividing lines in bacteria, seems to be involved with segregation of
newly replicated chromosome
•Found in both G+ , G -
•Infoldings of the bacterial cytoplasmic membrane seen as spherical structure
•Their function is not precisely known
(previously thought to be artifacts during preparing bacterial specimens for electron microscopy)
•Often found near septa or dividing lines in bacteria, seems to be involved with segregation of
newly replicated chromosome
Mesosomes
Functions of cytoplasmic membrane
1.Membranes and antibiotics (Polymyxin B, Gramicidin)
Disinfectants and antiseptics (Orthophenylphenol, Alcohol)
2.Selective permeability
3.The site for energy production (Electron transport system)
a- respiration (aerobic, anaerobic)
Organic or inorganic compounds breaking go to
contain high energy electron oxidation Electron membrane
during this process, protons transported out the cell A series of electron carriers
1.Membranes and antibiotics (Polymyxin B, Gramicidin)
Disinfectants and antiseptics (Orthophenylphenol, Alcohol)
2.Selective permeability
3.The site for energy production (Electron transport system)
a- respiration (aerobic, anaerobic)
Organic or inorganic compounds breaking go to
contain high energy electron oxidation Electron membrane
during this process, protons transported out the cell A series of electron carriers
The outside of the membrane becomes positively charged and the inside becomes negatively charged
(this proton gradient energizes the membrane)
The energy can be used to do work directly (the proton motive force)
stored in ATP
b- photosynthetic cells
light excites electrons a series of electron carriers proton motive force or
ATP is generated
4.The site of peptidoglycan synthesis (growing, dividing cells)
5.The site of phospholipid synthesis and some proteins (for synthesis of cytoplasmic membrane)
(this proton gradient energizes the membrane)
The energy can be used to do work directly (the proton motive force)
stored in ATP
b- photosynthetic cells
light excites electrons a series of electron carriers proton motive force or
ATP is generated
4.The site of peptidoglycan synthesis (growing, dividing cells)
5.The site of phospholipid synthesis and some proteins (for synthesis of cytoplasmic membrane)
6. Involved in amitotic division of the nucleoid
7. Contain the bases of flagella
8. The site of waste removal
9. Involved in the formation of endospores
7. Contain the bases of flagella
8. The site of waste removal
9. Involved in the formation of endospores
The Cell Wall
•A complex semi rigid structure responsible for maintenance of the shape, integrity of the cell and prevents
osmotic lysis
•Surrounds the fragile plasma membrane and protects it.
•Lysozyme (body fluids).
•Lysozyme has unrestricted access to the cell wall of gram + bacteria.
•Gram – bacteria must be treated with chelating agent such as ethylenediaminetetra acetic acid (EDTA),
withdraw magnesium ions from the outer membrane leading to release of specific outer components and
increase permeability of the membrane.
•Mycoplasmas lack a cell wall, their cytoplasmic membrane contain sterols.
•Archaebacterial cell wall composed of chemicals distinct from peptidoglycan such as protein or
pseudomurein.
•A complex semi rigid structure responsible for maintenance of the shape, integrity of the cell and prevents
osmotic lysis
•Surrounds the fragile plasma membrane and protects it.
•Lysozyme (body fluids).
•Lysozyme has unrestricted access to the cell wall of gram + bacteria.
•Gram – bacteria must be treated with chelating agent such as ethylenediaminetetra acetic acid (EDTA),
withdraw magnesium ions from the outer membrane leading to release of specific outer components and
increase permeability of the membrane.
•Mycoplasmas lack a cell wall, their cytoplasmic membrane contain sterols.
•Archaebacterial cell wall composed of chemicals distinct from peptidoglycan such as protein or
pseudomurein.
•Peptidoglycan (Murein).
•Polymer of interlocking chains of identical
glycopeptides (peptidoglycan monomers).
•Monomers consists of two joined amino sugars
N-acetylglucoseamine (NAG), N-acetylmuramic
acid (NAM).
•Tetra peptide coming of NAM.
•Monomers bonded together to form chains of
linked peptidoglycan subunits.
•Individual chains are joined by means of cross
links (between tetra peptides = tremendous
strength).
The cell wall composition
•Polymer of interlocking chains of identical
glycopeptides (peptidoglycan monomers).
•Monomers consists of two joined amino sugars
N-acetylglucoseamine (NAG), N-acetylmuramic
acid (NAM).
•Tetra peptide coming of NAM.
•Monomers bonded together to form chains of
linked peptidoglycan subunits.
•Individual chains are joined by means of cross
links (between tetra peptides = tremendous
strength).
The cell wall composition
•Many variations in chemical composition of the
peptidoglycan restricted to:
A- the nature of amino acids of tetrapeptids (specially 3-
position).
•L-lysine is found in many cocci (S. aureus), some other
species contain L-ornithine, L-homoserine.
•In most G +, - bacilli cross linkage between free amino
group in position-3 and terminal carboxyl group of D-
alanine at position-4 on an adjacent glycan strand.
B- the muramic acid itself; half of muramic acid residues in S.
aureus bear an acetyl group on the 6-position (insensitive to
Lysozyme), the same modification reported in Proteus,
Neisseria and Pseudomonas.
peptidoglycan restricted to:
A- the nature of amino acids of tetrapeptids (specially 3-
position).
•L-lysine is found in many cocci (S. aureus), some other
species contain L-ornithine, L-homoserine.
•In most G +, - bacilli cross linkage between free amino
group in position-3 and terminal carboxyl group of D-
alanine at position-4 on an adjacent glycan strand.
B- the muramic acid itself; half of muramic acid residues in S.
aureus bear an acetyl group on the 6-position (insensitive to
Lysozyme), the same modification reported in Proteus,
Neisseria and Pseudomonas.
Assembly of peptidoglycan monomers
•A peptide is first attached to NAM
•The NAM-peptide complex then attaches to a
phosphorylated bactoprenol (C55) molecule
(located in the cytoplasmic membrane).
•NAG then bonds to the NAM to form the
peptidoglycan monomers of NAG-NAM-peptide
which are transported across the cytoplasmic
membrane by the bactoprenol.
•A peptide is first attached to NAM
•The NAM-peptide complex then attaches to a
phosphorylated bactoprenol (C55) molecule
(located in the cytoplasmic membrane).
•NAG then bonds to the NAM to form the
peptidoglycan monomers of NAG-NAM-peptide
which are transported across the cytoplasmic
membrane by the bactoprenol.
Assembly of peptidoglycan monomers
•During normal bacterial growth, to increase their size following binary fission bacterial enzymes
(autolysins) breaks the cross links in the peptidoglycan to allow insertion of peptidoglycan
building blocks (monomers of NAG-NAM-peptide) .
•While transpeptidase enzymes;
* join the peptide of one monomer with that of another to provide
strength to the cell wall.(types of transpeptidase determines the shape of bacterium).
* Add new peptidoglycan monomers and reseal the wall
•During normal bacterial growth, to increase their size following binary fission bacterial enzymes
(autolysins) breaks the cross links in the peptidoglycan to allow insertion of peptidoglycan
building blocks (monomers of NAG-NAM-peptide) .
•While transpeptidase enzymes;
* join the peptide of one monomer with that of another to provide
strength to the cell wall.(types of transpeptidase determines the shape of bacterium).
* Add new peptidoglycan monomers and reseal the wall
Antibiotics inhibit normal synthesis of peptidoglycan
•Inhibit normal synthesis of peptidoglycan by bacteria causing them to burst as a result of osmotic
lysis.
•Interfere with functions of autolysins and transpeptidase enzymes.
•EX; Penicillins (penicillin G, oxacillin, ampicillin and amoxicillin)
and cephalosporins (ceftriaxone, cefixime, cefoxitin and cephalothin)
•Bind to the transpeptidase enzymes (also called penicillin-binding proteins).
Blocks the transpeptidase enzymes from cross-linking the sugar chains, results in a weak cell wall
Osmotic lysis of the bacterium.
•Inhibit normal synthesis of peptidoglycan by bacteria causing them to burst as a result of osmotic
lysis.
•Interfere with functions of autolysins and transpeptidase enzymes.
•EX; Penicillins (penicillin G, oxacillin, ampicillin and amoxicillin)
and cephalosporins (ceftriaxone, cefixime, cefoxitin and cephalothin)
•Bind to the transpeptidase enzymes (also called penicillin-binding proteins).
Blocks the transpeptidase enzymes from cross-linking the sugar chains, results in a weak cell wall
Osmotic lysis of the bacterium.
•Glycopeptides (vancomycin):
* Bind directly to the cell wall peptides and block the transpeptidase enzymes from
cross linking the sugar chains between monomers (NAG-NAM-peptide).
* Block Transglycolation (the bonding of the NAMs of one monomer to the NAGs of
another).
weak cell wall and osmotic lysis of the bacterium
* Bind directly to the cell wall peptides and block the transpeptidase enzymes from
cross linking the sugar chains between monomers (NAG-NAM-peptide).
* Block Transglycolation (the bonding of the NAMs of one monomer to the NAGs of
another).
weak cell wall and osmotic lysis of the bacterium
Bacteria can be placed in one of three groups
according to staining
•Gram-positive: retain CV purple. Ex, Streptococcus pyogenes, Staphylococcus aureus.
•Gram-negative: retain Safranin pink. Ex, Klebsiella pneumonia, E. coli.
•Acid-fast: retain carbolfuchsin red + ve. Ex, Mycobacterium tuberculosis,
Mycobacterium leprae.
retain Methylene blue blue - Ve.
•These staining reactions are due to fundamental differences in their cell wall.
according to staining
•Gram-positive: retain CV purple. Ex, Streptococcus pyogenes, Staphylococcus aureus.
•Gram-negative: retain Safranin pink. Ex, Klebsiella pneumonia, E. coli.
•Acid-fast: retain carbolfuchsin red + ve. Ex, Mycobacterium tuberculosis,
Mycobacterium leprae.
retain Methylene blue blue - Ve.
•These staining reactions are due to fundamental differences in their cell wall.
Gram positive cell wall
•Electron micrograph of gram
positive cell wall.
•Appears thick.
•Electron micrograph of gram
positive cell wall.
•Appears thick.
Gram Positive cell
wall
•A broad dense wall 20-80 nm thick.
•Numerous interconnecting layers of
peptidoglycan (60-90 % of cell wall).
•Interwoven by teichoic acid;
(Composed of polymers of glycerol,
phosphates and the sugar alcohol ribitol)
Extended through and beyond cell wall.
Some have a lipid attached (lipoteichoic
acid).
•The outer surface of the peptidoglycan is
studded with proteins which differ with
the strain of bacteria.
wall
•A broad dense wall 20-80 nm thick.
•Numerous interconnecting layers of
peptidoglycan (60-90 % of cell wall).
•Interwoven by teichoic acid;
(Composed of polymers of glycerol,
phosphates and the sugar alcohol ribitol)
Extended through and beyond cell wall.
Some have a lipid attached (lipoteichoic
acid).
•The outer surface of the peptidoglycan is
studded with proteins which differ with
the strain of bacteria.
The Cell Wall Functions
1- The peptidoglycan gives the bacterium its shape and prevent osmotic lysis,
Teichoic acid make the cell wall stronger.
2- considered as pathogen-associated molecular patterns (During infection);
* peptidoglycan and teichoic acid considered as pathogen-associated molecular patterns
( molecules unique to M.O and not associated with human cells)
* Pattern-recognition receptors on defense cells of the body, binds to peptidoglycan & teichoic
acid triggers innate immune defenses such as inflammation, fever and phagocytosis.
3- The peptidoglycan and teichoic acids also activate the alternative complement pathway and the lectin
pathway (body defense).
1- The peptidoglycan gives the bacterium its shape and prevent osmotic lysis,
Teichoic acid make the cell wall stronger.
2- considered as pathogen-associated molecular patterns (During infection);
* peptidoglycan and teichoic acid considered as pathogen-associated molecular patterns
( molecules unique to M.O and not associated with human cells)
* Pattern-recognition receptors on defense cells of the body, binds to peptidoglycan & teichoic
acid triggers innate immune defenses such as inflammation, fever and phagocytosis.
3- The peptidoglycan and teichoic acids also activate the alternative complement pathway and the lectin
pathway (body defense).
Pathogen Detection
•Peptidoglycan monomers (NAG-NAM
–tetrapeptide) and teichoic acids are recognized by
defense cells of the body ( CD14 receptor on
macrophages )and trigger toll-like receptor (TLR
-2) to release various defense chemicals (cytokines)
ex; 1L-1,1l-6 which bind to cytokine receptors on
target cells and initiate inflammation (one of first
step of body defense) as well as activating both the
complement pathways and coagulation pathways.
Similar to endotoxin (LPS) from the Gram-
negative Cell Wall
•Peptidoglycan monomers (NAG-NAM
–tetrapeptide) and teichoic acids are recognized by
defense cells of the body ( CD14 receptor on
macrophages )and trigger toll-like receptor (TLR
-2) to release various defense chemicals (cytokines)
ex; 1L-1,1l-6 which bind to cytokine receptors on
target cells and initiate inflammation (one of first
step of body defense) as well as activating both the
complement pathways and coagulation pathways.
Similar to endotoxin (LPS) from the Gram-
negative Cell Wall
4- Surface proteins on peptidoglycan
•Functioning as enzymes.
•Serving as adhesions (to host cells and
other surfaces, resist flushing).
•Functioning as invasions ( penetrate
host cells).
• Aiding certain bacteria in resisting
phagocytic destruction
•Functioning as enzymes.
•Serving as adhesions (to host cells and
other surfaces, resist flushing).
•Functioning as invasions ( penetrate
host cells).
• Aiding certain bacteria in resisting
phagocytic destruction
Gram negative cell wall
•Decolorize during Gram stain, pick up the
counterstain (Safranin) and appear Pink.
•Common Gram – of medical importance;
Salmonella, Shigella, Neisseria,
Hemophilus influenzae, Escerichia coli and
klebsiella pneumoniae.
•Appears multilayered in electron micrograph
•Decolorize during Gram stain, pick up the
counterstain (Safranin) and appear Pink.
•Common Gram – of medical importance;
Salmonella, Shigella, Neisseria,
Hemophilus influenzae, Escerichia coli and
klebsiella pneumoniae.
•Appears multilayered in electron micrograph
Gram negative cell
wall
•Appears multilayered.
•A thin, inner wall composed of 2-3
layers of peptidoglycan
(2-3 nm / 10-20 % of cell wall).
•Peptidoglycan gives the bacterium
its shape and prevents osmotic lysis.
wall
•Appears multilayered.
•A thin, inner wall composed of 2-3
layers of peptidoglycan
(2-3 nm / 10-20 % of cell wall).
•Peptidoglycan gives the bacterium
its shape and prevents osmotic lysis.
•Gram negative Cell Wall Consist of ;
1- Peptidoglycan layer. a thin inner wall composed of 2-3 layers of peptidoglycan (2-3 nm / 10-20 % of cell
wall).
2- An outer membrane; a lipid bilayer about 7 nm thick composed of:
a- phospholipids: located mainly in the inner layer of the outer membrane, as are the lipoproteins
that connect the outer membrane to the peptidoglycan.
b- Lipopolysaccharides (LPS): located in the outer layer of the outer membrane, consist of a lipid
portion (lipid A) imbedded in the membrane and a polysaccharide portion extending outward
from the bacterial surface.
c- proteins: the outer membrane contains a number of proteins that differ with the strain and species of
the bacterium).
1- Peptidoglycan layer. a thin inner wall composed of 2-3 layers of peptidoglycan (2-3 nm / 10-20 % of cell
wall).
2- An outer membrane; a lipid bilayer about 7 nm thick composed of:
a- phospholipids: located mainly in the inner layer of the outer membrane, as are the lipoproteins
that connect the outer membrane to the peptidoglycan.
b- Lipopolysaccharides (LPS): located in the outer layer of the outer membrane, consist of a lipid
portion (lipid A) imbedded in the membrane and a polysaccharide portion extending outward
from the bacterial surface.
c- proteins: the outer membrane contains a number of proteins that differ with the strain and species of
the bacterium).
The outer membrane like the cytoplasmic membrane, is semipermeable:
act as a coarse molecular sieve, small molecules pass through due to pores running through the
membrane. These pores are composed of proteins called Porins ( proteins that form pores in the outer
membrane wide enough to allow passage of most small hydrophilic molecules into the periplasmic
space , across the cytoplasmic membrane (larger or hydrophobic molecules cannot penetrate the outer
membrane)
act as a coarse molecular sieve, small molecules pass through due to pores running through the
membrane. These pores are composed of proteins called Porins ( proteins that form pores in the outer
membrane wide enough to allow passage of most small hydrophilic molecules into the periplasmic
space , across the cytoplasmic membrane (larger or hydrophobic molecules cannot penetrate the outer
membrane)
Lipopolysaccharide (LPS)
Composed of two parts:
•Lipid A: is a derivative of 2 NAG units with
up to 7 fatty acids connected to it that
anchor the LPS in the membrane.
•Attached to lipid A;
1- a conserved core polysaccharide that
contains; KDO ( keto-deoxyoctulosonate),
heptose, glucose and glucosamine
sugars (unusual sugars).
2- the rest of the polysaccharide consists of
repeating sugar units (O-antigen or
O-polysaccharide).
Composed of two parts:
•Lipid A: is a derivative of 2 NAG units with
up to 7 fatty acids connected to it that
anchor the LPS in the membrane.
•Attached to lipid A;
1- a conserved core polysaccharide that
contains; KDO ( keto-deoxyoctulosonate),
heptose, glucose and glucosamine
sugars (unusual sugars).
2- the rest of the polysaccharide consists of
repeating sugar units (O-antigen or
O-polysaccharide).
• The O-antigen:
is exposed to the outer environment and host defenses will often raise antibodies to this
structure (considered as antigen).
varies between species and even between various isolates of a species.
Bacteria protect themselves by varying the make-up of the O-antigen.
Involved in recognition by certain bacteriophage.
is exposed to the outer environment and host defenses will often raise antibodies to this
structure (considered as antigen).
varies between species and even between various isolates of a species.
Bacteria protect themselves by varying the make-up of the O-antigen.
Involved in recognition by certain bacteriophage.
LPS:
Confers a negative charge and repels hydrophobic molecules. Some G – species live in gut of
mammals and LPS will repel fat solubilizing bile (gal bladder secrets).
Medically important; free LPS in solution is toxic (endotoxin), when released from bacterial cells
is toxic to mammals creating a wide spectrum of physiological changes such as:
Induction of fever (Pyrogenic).
Changes in white blood cells counts.
Leaking blood vessels.
Tumor necrosis.
Dropping blood pressure leading to vascular collapse and eventually shock
May be lethal (at high concentration).
Confers a negative charge and repels hydrophobic molecules. Some G – species live in gut of
mammals and LPS will repel fat solubilizing bile (gal bladder secrets).
Medically important; free LPS in solution is toxic (endotoxin), when released from bacterial cells
is toxic to mammals creating a wide spectrum of physiological changes such as:
Induction of fever (Pyrogenic).
Changes in white blood cells counts.
Leaking blood vessels.
Tumor necrosis.
Dropping blood pressure leading to vascular collapse and eventually shock
May be lethal (at high concentration).
Functions of the outer membrane
•Its semipermeable nature helps retain certain enzymes and prevents some toxic substances e.g.
Penicillin G and Lysozyme from entering .
•LPS from the outer membrane of G- cell wall add strength to the outer membrane, similar to
glycopeptides and teichoic acids of G + cell wall.
•Body defense start by detecting the presence of M.O. by recognizing molecules unique to M.O. that
are not associated with human cells (pathogen associated molecular patterns ex; LPS). LPS binds to
pattern recognition receptors (on defense cells) and triggers innate immune defenses such as
inflammation, fever and phagocytosis.
•The LPS activates the alternative complement pathway and the Lectin pathway (defense pathways
in the body).
•LPS when released, functions as a harmful endotoxin.
•Confers negative charge to cell and stabilizes mating cells.
•Its semipermeable nature helps retain certain enzymes and prevents some toxic substances e.g.
Penicillin G and Lysozyme from entering .
•LPS from the outer membrane of G- cell wall add strength to the outer membrane, similar to
glycopeptides and teichoic acids of G + cell wall.
•Body defense start by detecting the presence of M.O. by recognizing molecules unique to M.O. that
are not associated with human cells (pathogen associated molecular patterns ex; LPS). LPS binds to
pattern recognition receptors (on defense cells) and triggers innate immune defenses such as
inflammation, fever and phagocytosis.
•The LPS activates the alternative complement pathway and the Lectin pathway (defense pathways
in the body).
•LPS when released, functions as a harmful endotoxin.
•Confers negative charge to cell and stabilizes mating cells.
•LPS binds to LPS-binding protein circulating in the
blood.
•This complex binds to a receptor molecule (CD14)
found on surface of macrophage.
•This promote Toll-like receptor TLR-4 to respond
to LPS , triggering macrophages to release
cytokines (defense regulatory chemicals) including
IL-1, IL-6, IL-8 , TNF-alpha and PAF.
•Cytokines bind to cytokines receptors on target
cells and initiate inflammation and activate both
the complement pathway and the coagulation
pathway.
blood.
•This complex binds to a receptor molecule (CD14)
found on surface of macrophage.
•This promote Toll-like receptor TLR-4 to respond
to LPS , triggering macrophages to release
cytokines (defense regulatory chemicals) including
IL-1, IL-6, IL-8 , TNF-alpha and PAF.
•Cytokines bind to cytokines receptors on target
cells and initiate inflammation and activate both
the complement pathway and the coagulation
pathway.
Surface proteins in the outer membrane function as:
•Function as enzymes.
•Serving as adhesins to colonize and resist flushing.
•Functioning as invasions, penetrate host cells.
•Aiding certain bacteria in resisting Phagocytic destruction.
•Function as enzymes.
•Serving as adhesins to colonize and resist flushing.
•Functioning as invasions, penetrate host cells.
•Aiding certain bacteria in resisting Phagocytic destruction.
The periplasm
•The gelatinous material between the outer membrane, the peptidoglycan and the cytoplasmic
membrane
which contains many different proteins (enzymes) .
•These proteins function to detect the environment and transport needed nutrients into the cell.
•Periplasmic enzymes include:
1- hydrolytic enzymes.
phosphatases, degrade phosphate containing compounds
proteases, degrade proteins and peptides
Endonucleases, degrade nucleic acids
•The gelatinous material between the outer membrane, the peptidoglycan and the cytoplasmic
membrane
which contains many different proteins (enzymes) .
•These proteins function to detect the environment and transport needed nutrients into the cell.
•Periplasmic enzymes include:
1- hydrolytic enzymes.
phosphatases, degrade phosphate containing compounds
proteases, degrade proteins and peptides
Endonucleases, degrade nucleic acids
2- binding proteins, recognize specific solutes and transport across membrane;
sugars, aminoacids, inorganic ions and vitamins.
3- chemoreceptors; help cell interpret chemical composition of its environment.
4- detoxifying enzymes; alter harmful agents before they get into cell. Ex, beta-lactamase.
5- osmotic protection; when cell is put in high osmolarity. Compatible solutes accumulate in
periplasm.
sugars, aminoacids, inorganic ions and vitamins.
3- chemoreceptors; help cell interpret chemical composition of its environment.
4- detoxifying enzymes; alter harmful agents before they get into cell. Ex, beta-lactamase.
5- osmotic protection; when cell is put in high osmolarity. Compatible solutes accumulate in
periplasm.
Difference between G+, G- cell wall
Property G + G -
Thickness of wall 20 – 80 nm 10 nm
Number of layers in wall 1 2
Peptidoglycan content > 50 % 10 - 20 %
Teichoic acid in wall + -
Lipid and lipoprotein content 0 – 3 % 58 %
Protein content 0 9 %
lipopolysaccharide 0 13 %
Sensitive to penicillin + - (not as)
Digested by lysozyme + - (not as much)
Porin - +
Property G + G -
Thickness of wall 20 – 80 nm 10 nm
Number of layers in wall 1 2
Peptidoglycan content > 50 % 10 - 20 %
Teichoic acid in wall + -
Lipid and lipoprotein content 0 – 3 % 58 %
Protein content 0 9 %
lipopolysaccharide 0 13 %
Sensitive to penicillin + - (not as)
Digested by lysozyme + - (not as much)
Porin - +
Gram Positive Cell Wall Gram Negative Cell Wall
Acid Fast bacteria
•Genus -1
Mycobacterium tuberculosis
Mycobacterium leprae
•Genus -2
Nocardia
•Acid fast stain
•Acid fast cell wall resist decolorization with acid-alcohol mixture.
•Stain red (the color of the initial stain, carbol fuchsin).
•Other bacteria will be decolorized and stain blue (the color of the counter stain, methylene blue).
•The waxy lipid (Mycolic acid) approximately 60% of the wall, makes the wall impermeable.
•Genus -1
Mycobacterium tuberculosis
Mycobacterium leprae
•Genus -2
Nocardia
•Acid fast stain
•Acid fast cell wall resist decolorization with acid-alcohol mixture.
•Stain red (the color of the initial stain, carbol fuchsin).
•Other bacteria will be decolorized and stain blue (the color of the counter stain, methylene blue).
•The waxy lipid (Mycolic acid) approximately 60% of the wall, makes the wall impermeable.
Acid fast cell wall
•Small amounts of peptidoglycan.
•Large amounts of glycolipids;
* Mycolic acid ( a waxy lipid, 60 %
of the wall).
*Arabinogalactan-lipid complex
* lipoarabinomannan.
•Small amounts of peptidoglycan.
•Large amounts of glycolipids;
* Mycolic acid ( a waxy lipid, 60 %
of the wall).
*Arabinogalactan-lipid complex
* lipoarabinomannan.
Functions of Mycobacteria Cell Wall
•Peptidoglycan; gives the bacterium its shape and prevents osmotic lysis.
•Mycolic acid and other glycolipids; impede the entry of chemicals causing the organism to grow
slowly and be more resistant to chemical agents and lysosomal components of phagocytes than
most bacteria.
•The lysis of Mycobacterium releases mycolic acid and muramyl dipeptide from cell wall, which
binds to receptors on macrophages causing them to release cytokines such as tumor necrosis
factor-alpha (TNF-alpha).
•Inflammatory effects of TNF-alpha and release of toxic lysosomal components of the
macrophages (to kill Mycobacterium) causing lung damage.
•Peptidoglycan; gives the bacterium its shape and prevents osmotic lysis.
•Mycolic acid and other glycolipids; impede the entry of chemicals causing the organism to grow
slowly and be more resistant to chemical agents and lysosomal components of phagocytes than
most bacteria.
•The lysis of Mycobacterium releases mycolic acid and muramyl dipeptide from cell wall, which
binds to receptors on macrophages causing them to release cytokines such as tumor necrosis
factor-alpha (TNF-alpha).
•Inflammatory effects of TNF-alpha and release of toxic lysosomal components of the
macrophages (to kill Mycobacterium) causing lung damage.
Bacterial lacking cell wall
•One example; Mycoplasma species.
•Pleomorphic.
•Quickly killed if placed in an environment with very high or very low salt concentrations. So, they
are obligate intracellular pathogens
•It has tough membrane due to the presence of sterols, which make the membrane more resistant to
rupture than in other bacteria.
•Some bacteria may mutate or suffering extreme nutritional conditions to form a cell wall –less
forms or L-forms (partial or complete loss of the cell wall).
•L-Form is observed in both G – and + , have varied shape and sensitive to osmotic shock.
•One example; Mycoplasma species.
•Pleomorphic.
•Quickly killed if placed in an environment with very high or very low salt concentrations. So, they
are obligate intracellular pathogens
•It has tough membrane due to the presence of sterols, which make the membrane more resistant to
rupture than in other bacteria.
•Some bacteria may mutate or suffering extreme nutritional conditions to form a cell wall –less
forms or L-forms (partial or complete loss of the cell wall).
•L-Form is observed in both G – and + , have varied shape and sensitive to osmotic shock.
Mycoplasma
Functions of the cell wall
•Confers a shape to the bacteria, certain bacteria have long appendages that increase surface area, allow
cells to live in very dilute environments.
•Directly contact with the environment (interactions with outside world may determine survival of cells);
* interaction with a host cell in the intestine to begin attachment.
* binding to a virus (bacteriophage).
•Involved in many pathogenic properties of the bacteria, attachment to specific host cells during infection
stage, can be a pathogenic determinate.
•Act as a barrier to some molecules, G+ cell wall have a negative charge and are hydrophilic (teichoic
acid), this act as a barrier to molecules with a negative charge. G – cell walls are very hydrophilic (LPS in
outer membrane). The LPS act as a barrier to hydrophobic molecules (resistant to hydrophobic
compounds like crystal violet and bile).
•Confers a shape to the bacteria, certain bacteria have long appendages that increase surface area, allow
cells to live in very dilute environments.
•Directly contact with the environment (interactions with outside world may determine survival of cells);
* interaction with a host cell in the intestine to begin attachment.
* binding to a virus (bacteriophage).
•Involved in many pathogenic properties of the bacteria, attachment to specific host cells during infection
stage, can be a pathogenic determinate.
•Act as a barrier to some molecules, G+ cell wall have a negative charge and are hydrophilic (teichoic
acid), this act as a barrier to molecules with a negative charge. G – cell walls are very hydrophilic (LPS in
outer membrane). The LPS act as a barrier to hydrophobic molecules (resistant to hydrophobic
compounds like crystal violet and bile).
Cytoplasm
•Refers to everything enclosed by the cytoplasmic membrane.
• Composed of 80 % water.
•It contains;
Nucleic acid (DNA, RNA).
Enzymes
Amino acids
Carbohydrates
Lipids
Inorganic ions
Many low molecular weight compounds
•The liquid components of the cytoplasm is called Cytosol.
•Some groups of bacteria produce cytoplasmic inclusion bodies that carry out specialized cellular
functions.
•Refers to everything enclosed by the cytoplasmic membrane.
• Composed of 80 % water.
•It contains;
Nucleic acid (DNA, RNA).
Enzymes
Amino acids
Carbohydrates
Lipids
Inorganic ions
Many low molecular weight compounds
•The liquid components of the cytoplasm is called Cytosol.
•Some groups of bacteria produce cytoplasmic inclusion bodies that carry out specialized cellular
functions.
Functions of cytoplasm
•The site of most bacterial metabolism;
Catabolism, molecules are broken down in order to obtain building block molecules for
more complex molecules and macromolecules.
Anabolism, to synthesize other molecules and macromolecules.
•The chemical reactions occurring within the bacterium are under the control of endoenzymes.
•The site of most bacterial metabolism;
Catabolism, molecules are broken down in order to obtain building block molecules for
more complex molecules and macromolecules.
Anabolism, to synthesize other molecules and macromolecules.
•The chemical reactions occurring within the bacterium are under the control of endoenzymes.
The nucleoid
•Composition:
The term Genome refers to the sum of an organism’s genetic material.
Bacterial genome is composed of chromosomal DNA and represents the bacterium’s nucleoid.
unlike eukaryotes, no nuclear membrane or nucleoli.
Bacterial nucleoid does not divide by meiosis or mitosis.
Bacteria are haploid (only one chromosome), only reproduce a sexually, the cytoplasmic
membrane plays a role in DNA separation during bacterial replication.
•The nucleoid:
is one long, single molecule of double stranded DNA, helical, supercoiled DNA.
In most bacteria, the 2 ends of the double-stranded DNA covalently bond together to form a circle.
The chromosome around 1000 µm long, contains as many as 3500 genes.
E. coli, which is 2-3 µm length has 1400 µm chromosome
•Composition:
The term Genome refers to the sum of an organism’s genetic material.
Bacterial genome is composed of chromosomal DNA and represents the bacterium’s nucleoid.
unlike eukaryotes, no nuclear membrane or nucleoli.
Bacterial nucleoid does not divide by meiosis or mitosis.
Bacteria are haploid (only one chromosome), only reproduce a sexually, the cytoplasmic
membrane plays a role in DNA separation during bacterial replication.
•The nucleoid:
is one long, single molecule of double stranded DNA, helical, supercoiled DNA.
In most bacteria, the 2 ends of the double-stranded DNA covalently bond together to form a circle.
The chromosome around 1000 µm long, contains as many as 3500 genes.
E. coli, which is 2-3 µm length has 1400 µm chromosome
•Histone-like proteins bind to the DNA, segregating DNA molecule into around 50 chromosomal domains ,
making it more compact.
•Enzyme called DNA gyrase supercoiled each domain around itself forming a compacted, supercoiled
mass of DNA (0.2 µm diameter).
•Projections of the nucleoid extend into the cytoplasm, these projections contain DNA that is being
transcribed into mRNA.
•DNA topoisomerases: essential enzymes in the unwinding, replication and rewinding of the circular,
supercoiled DNA during replication and transcription.
making it more compact.
•Enzyme called DNA gyrase supercoiled each domain around itself forming a compacted, supercoiled
mass of DNA (0.2 µm diameter).
•Projections of the nucleoid extend into the cytoplasm, these projections contain DNA that is being
transcribed into mRNA.
•DNA topoisomerases: essential enzymes in the unwinding, replication and rewinding of the circular,
supercoiled DNA during replication and transcription.
Functions of the nucleoid
•Is the genetic material of the bacterium.
•DNA determines what proteins and enzymes an organism can synthesize, then, what chemical reactions
it is able to carry out.
•Genes located along the DNA are transcribed into RNA, which in case of mRNA is translated into
protein at the ribosomes.
•May act as a pathogen-associated molecular patterns;
Bacterial and viral genomes contain a high frequency of unmethylated cytosine-guanine
dinucleotide sequences.
Mammalian DNA has a low frequency of cytosine-guanine dinucleotides and most are
methylated.
•Bacterial DNA binds to receptors on a variety of defense cells of the body and triggers innate immune
defense as inflammation, fever and phagocytosis
•Is the genetic material of the bacterium.
•DNA determines what proteins and enzymes an organism can synthesize, then, what chemical reactions
it is able to carry out.
•Genes located along the DNA are transcribed into RNA, which in case of mRNA is translated into
protein at the ribosomes.
•May act as a pathogen-associated molecular patterns;
Bacterial and viral genomes contain a high frequency of unmethylated cytosine-guanine
dinucleotide sequences.
Mammalian DNA has a low frequency of cytosine-guanine dinucleotides and most are
methylated.
•Bacterial DNA binds to receptors on a variety of defense cells of the body and triggers innate immune
defense as inflammation, fever and phagocytosis
Antibacterial inhibiting nucleic acid replication
•The fluoroquinolones (Norfloxacin and ciprofloxacin);
Inhibiting one or more of the topoisomerases, the enzymes needed for bacterial nucleic acid
synthesis.
•Co-trimoxazole (a combination of sulfamethoxazole and trimethoprim);
Block enzymes required for synthesis of tetrahydrofolic acid, a cofactor needed for synthesis
of nucleotide bases (thymine, guanine, uracil and adenine).
•The fluoroquinolones (Norfloxacin and ciprofloxacin);
Inhibiting one or more of the topoisomerases, the enzymes needed for bacterial nucleic acid
synthesis.
•Co-trimoxazole (a combination of sulfamethoxazole and trimethoprim);
Block enzymes required for synthesis of tetrahydrofolic acid, a cofactor needed for synthesis
of nucleotide bases (thymine, guanine, uracil and adenine).
Competitive antagonism
•The drug chemically resembles a substrate.
•While the enzyme is bound to the drug, it is
unable to bind to its natural substrate, blocks that
step in the metabolic pathway.
•Sulfonamides such as sulfamethoxazole tie up the
first enzyme, blocks conversion of para amino
benzoic acid to dihydropteroic acid.
•Trimethoprim bind to the third enzyme, blocks
conversion of dihydrofolic acid to tetrahydrofolic
acid.
•The drug chemically resembles a substrate.
•While the enzyme is bound to the drug, it is
unable to bind to its natural substrate, blocks that
step in the metabolic pathway.
•Sulfonamides such as sulfamethoxazole tie up the
first enzyme, blocks conversion of para amino
benzoic acid to dihydropteroic acid.
•Trimethoprim bind to the third enzyme, blocks
conversion of dihydrofolic acid to tetrahydrofolic
acid.
plasmids
•Small nonchromosomal, helical double stranded DNA molecules, contain 5-100 genes.
•The tow ends of the double stranded DNA molecules covalently bond together forming a circle.
•Not essential for normal bacterial growth, bacteria may lose or gain them without harm.
•Provide an advantage under certain environmental conditions.
Bacteria have a plasmid coding for an enzyme capable of denaturing a particular antibiotic.
if that bacterium enter the body, the particular antibiotic given as treatment, the bacterium
containing the plasmid is able to survive and grow.
•Small nonchromosomal, helical double stranded DNA molecules, contain 5-100 genes.
•The tow ends of the double stranded DNA molecules covalently bond together forming a circle.
•Not essential for normal bacterial growth, bacteria may lose or gain them without harm.
•Provide an advantage under certain environmental conditions.
Bacteria have a plasmid coding for an enzyme capable of denaturing a particular antibiotic.
if that bacterium enter the body, the particular antibiotic given as treatment, the bacterium
containing the plasmid is able to survive and grow.
Functions of plasmids
•Coded for synthesis of a few proteins not coded for by the nucleoid.
•For example, R-plasmids, in G- negative bacteria coding for;
* production of a conjugation pilus, enables the bacterium to transfer a copy of R-
plasmid to other bacteria.
* multiple antibiotic resistance.
•Plasmids may coded for exotoxins such as tetanus exotoxins and enterotoxins such as E. coli enterotoxins.
•Coded for synthesis of a few proteins not coded for by the nucleoid.
•For example, R-plasmids, in G- negative bacteria coding for;
* production of a conjugation pilus, enables the bacterium to transfer a copy of R-
plasmid to other bacteria.
* multiple antibiotic resistance.
•Plasmids may coded for exotoxins such as tetanus exotoxins and enterotoxins such as E. coli enterotoxins.
Transposons
•Transposable elements "jumping genes“.
•Small pieces of DNA which encode enzymes (transpoase enzymes) that transpose the transposon, move it
from one DNA location to another.
•May be a part of bacterium’s nucleoid or in plasmids (1-12 genes long).
•Contains a number of genes, coding for antibiotic resistance or other traits, flanked at both ends by
insertion sequences coding for an enzyme (transpoase).
•Transpaose; the enzyme catalyzes the cutting and resealing of the DNA during transposition. Thus, such
transposons are able to cut themselves out of a bacterial nucleoid or a plasmid and insert themselves
into another nucleoid or plasmid and contribute in the transmission of antibiotic resistance among
population of bacteria.
•Transposable elements "jumping genes“.
•Small pieces of DNA which encode enzymes (transpoase enzymes) that transpose the transposon, move it
from one DNA location to another.
•May be a part of bacterium’s nucleoid or in plasmids (1-12 genes long).
•Contains a number of genes, coding for antibiotic resistance or other traits, flanked at both ends by
insertion sequences coding for an enzyme (transpoase).
•Transpaose; the enzyme catalyzes the cutting and resealing of the DNA during transposition. Thus, such
transposons are able to cut themselves out of a bacterial nucleoid or a plasmid and insert themselves
into another nucleoid or plasmid and contribute in the transmission of antibiotic resistance among
population of bacteria.
Integrons
•Are transposons that can carry multiple gene clusters called gene cassettes that move as unit from
one piece of DNA to another.
•Integrase enzyme; enables these gene cassettes to integrate and accumulate within the integron.
•In this way, a number of different antibiotic resistance genes can be transferred as a unit from one
bacterium to another.
•Are transposons that can carry multiple gene clusters called gene cassettes that move as unit from
one piece of DNA to another.
•Integrase enzyme; enables these gene cassettes to integrate and accumulate within the integron.
•In this way, a number of different antibiotic resistance genes can be transferred as a unit from one
bacterium to another.
Ribosomes
•Composition:
ribosomal RNA (rRNA) and protein.
two subunits with densities of 50S and 30S (S; a unit of density "Svedberg").
50S and 30S combine during protein synthesis to a complete 70S ribosome.
A typical bacterium may have as many as 15,000 ribosomes.
•Composition:
ribosomal RNA (rRNA) and protein.
two subunits with densities of 50S and 30S (S; a unit of density "Svedberg").
50S and 30S combine during protein synthesis to a complete 70S ribosome.
A typical bacterium may have as many as 15,000 ribosomes.
Functions of ribosomes
•Workbench for protein synthesis
•Receive & translate genetic
instructions for the formation of
specific proteins.
•During protein synthesis;
mRNA attaches to the 30S,
tRNAs attaches to 50 S
•Workbench for protein synthesis
•Receive & translate genetic
instructions for the formation of
specific proteins.
•During protein synthesis;
mRNA attaches to the 30S,
tRNAs attaches to 50 S
Antibiotics
•Many antibiotics alter bacterial ribosomes, interfering with translation and causing faulty protein
synthesis.
•The aminoglycosides (streptomycin, neomycin, gentamicin and amikacin). Binds irreversibly to the
30S and prevent the 50S from attaching to the translation initiation complex.
•By binding to the 30S, cause the misreading of the codons on mRNA, resulting in tRNA inserting the
wrong amino acids into the protein.
•The macrolides (Erythromycin, azithromycin and clarithromycin) bind reversibly to the 50S. They
inhibit elongation of the protein by the enzyme peptidyltransferase that forms peptide bonds
between the amino acids, by preventing the ribosome from translocating down the mRNA, or
both.
•Many antibiotics alter bacterial ribosomes, interfering with translation and causing faulty protein
synthesis.
•The aminoglycosides (streptomycin, neomycin, gentamicin and amikacin). Binds irreversibly to the
30S and prevent the 50S from attaching to the translation initiation complex.
•By binding to the 30S, cause the misreading of the codons on mRNA, resulting in tRNA inserting the
wrong amino acids into the protein.
•The macrolides (Erythromycin, azithromycin and clarithromycin) bind reversibly to the 50S. They
inhibit elongation of the protein by the enzyme peptidyltransferase that forms peptide bonds
between the amino acids, by preventing the ribosome from translocating down the mRNA, or
both.
Endospores
•A type of dormant cell, formed by a few groups of bacteria as intracellular structures , but ultimately
they are released as free endospores.
•Exhibit no signs of life (Cryptobiotic).
•Highly resistant to environmental stresses such as; temperature, irradiation, strong acids, disinfectants,
etc.
•The most durable cell produced in nature, they retain viability under appropriate environmental
conditions, they germinate back into vegetative cells.
•Endospores are formed by vegetative cells in response to environmental signals that indicate a limiting
factor for vegetative growth, such as exhaustion of an essential nutrient.
•Endospore formation is a mechanism of survival rather than a mechanism of reproduction.
•A type of dormant cell, formed by a few groups of bacteria as intracellular structures , but ultimately
they are released as free endospores.
•Exhibit no signs of life (Cryptobiotic).
•Highly resistant to environmental stresses such as; temperature, irradiation, strong acids, disinfectants,
etc.
•The most durable cell produced in nature, they retain viability under appropriate environmental
conditions, they germinate back into vegetative cells.
•Endospores are formed by vegetative cells in response to environmental signals that indicate a limiting
factor for vegetative growth, such as exhaustion of an essential nutrient.
•Endospore formation is a mechanism of survival rather than a mechanism of reproduction.
Electron micrograph of
Endospore
•Has a core wall of unique
peptidoglycan surrounded by
several layers including; the cortex,
the spore coat and the exosporium.
•The dehydrated core contains the
bacterial chromosome and a few
ribosomes and enzymes to jump-
start protein synthesis and
metabolism during germination.
Endospore
•Has a core wall of unique
peptidoglycan surrounded by
several layers including; the cortex,
the spore coat and the exosporium.
•The dehydrated core contains the
bacterial chromosome and a few
ribosomes and enzymes to jump-
start protein synthesis and
metabolism during germination.
Difference between endospores and vegetative cells
property Vegetative cells Endospores
Surface coats Typical gram-positive murein cell wall
polymer
Thick spore coat, cortex and peptidoglycan
core wall
Microscopic appearance Non-refractile Refractile
Calcium dipicolinic acid Absent Present in core
Cytoplasmic water
activity
High Very low
Enzymatic activity Present Absent
Macromolecular
synthesis
Present
Absent
Heat resistant Low High
Resistance to chemicals,
acids and radiation
Low High
Sensitivity to lysozyme Sensitive Resistant
Sensitivity to dyes and
staining
Sensitive Resistant
property Vegetative cells Endospores
Surface coats Typical gram-positive murein cell wall
polymer
Thick spore coat, cortex and peptidoglycan
core wall
Microscopic appearance Non-refractile Refractile
Calcium dipicolinic acid Absent Present in core
Cytoplasmic water
activity
High Very low
Enzymatic activity Present Absent
Macromolecular
synthesis
Present
Absent
Heat resistant Low High
Resistance to chemicals,
acids and radiation
Low High
Sensitivity to lysozyme Sensitive Resistant
Sensitivity to dyes and
staining
Sensitive Resistant
Organelles for bacterial photosynthesis
•There are 3 main groups of photosynthetic bacteria:
Oxygenic photosynthesis
Cyanobacteria
Anoxygenic photosynthesis
Green bacteria
Purple bacteria
•There are 3 main groups of photosynthetic bacteria:
Oxygenic photosynthesis
Cyanobacteria
Anoxygenic photosynthesis
Green bacteria
Purple bacteria
Cyanobacteria
•Oxygenic photosynthesis
•Water used as electron donor
•Generate oxygen during
photosynthesis
•The photosynthetic system is located
in an extensive thylakoid membrane
system that is lined with particles
called phycobilisomes.
•Oxygenic photosynthesis
•Water used as electron donor
•Generate oxygen during
photosynthesis
•The photosynthetic system is located
in an extensive thylakoid membrane
system that is lined with particles
called phycobilisomes.
Cyanobacteria
Green bacteria
•Anoxygenic photosynthesis
•Reduced molecules as; H2, H2S, S
and organic molecules are used
as an electron source
•Generate NADP, NADPH
•The photosynthetic system is
located in ellipsoidal vesicles
called chlorosomes that are
independent of the cytoplasmic
membrane
•Anoxygenic photosynthesis
•Reduced molecules as; H2, H2S, S
and organic molecules are used
as an electron source
•Generate NADP, NADPH
•The photosynthetic system is
located in ellipsoidal vesicles
called chlorosomes that are
independent of the cytoplasmic
membrane
Purple bacteria
•Anoxygenic photosynthesis
•Reduced molecules as; H2, H2S, S and organic molecules are used as an electron source
•Generate NADP, NADPH
•The photosynthetic system is located in spherical or lamellar membrane systems that are
continuous with the cytoplasmic membrane
•Anoxygenic photosynthesis
•Reduced molecules as; H2, H2S, S and organic molecules are used as an electron source
•Generate NADP, NADPH
•The photosynthetic system is located in spherical or lamellar membrane systems that are
continuous with the cytoplasmic membrane
Membrane systems of purple bacteria
Chromatophores
•Vesicular membrane
•Vesicles continuous with cytoplasmic membrane
Lamellar
•Lamellar membranes
•Continuous with cytoplasmic membrane, instead
of vesicles, forming membrane stacks
Chromatophores
•Vesicular membrane
•Vesicles continuous with cytoplasmic membrane
Lamellar
•Lamellar membranes
•Continuous with cytoplasmic membrane, instead
of vesicles, forming membrane stacks
Inclusion bodies
•Known as inclusions, considered as non-living cytoplasmic contents.
•Serve as a basis for identification.
•Cyanobacteria contain Cyanophycin granules (store nitrogen for bacteria).
•Cyanobacteria, nitrifying bacteria and other bacteria that reduces Co2 (fixation) to produce carbohydrates
contain carboxysomes ( these inclusions contain the enzyme ribulose-1,5-diphosphate carboxylase for
Co2 fixation through Calvin cycle.
•Purple and green photosynthetic bacteria and some aquatic bacteria contain gas vacuoles, that are
permeable to atmospheric gas, enable buoyancy.
•Known as inclusions, considered as non-living cytoplasmic contents.
•Serve as a basis for identification.
•Cyanobacteria contain Cyanophycin granules (store nitrogen for bacteria).
•Cyanobacteria, nitrifying bacteria and other bacteria that reduces Co2 (fixation) to produce carbohydrates
contain carboxysomes ( these inclusions contain the enzyme ribulose-1,5-diphosphate carboxylase for
Co2 fixation through Calvin cycle.
•Purple and green photosynthetic bacteria and some aquatic bacteria contain gas vacuoles, that are
permeable to atmospheric gas, enable buoyancy.
•Some bacteria produce inorganic inclusions as; Volutin (Metachromatic) granules, store sulfur and
inorganic phosphate that can be used in synthesis of ATP (characteristics of Corynebacterium diphtheriae).
•Some bacteria produce organic inclusion bodies containing either polyhydroxybutyrate or glycogen
granules for energy reserve.
•Polysaccharide inclusions consist of glycogen and starch (iodine gives reddish brown and blue color).
•Poly-ᵦ-hydroxybutyric acid is the common lipid storage material, can be detected by fat-soluble dyes
such as Sudan dyes .
•Some motile aquatic bacteria contain Magnetosomes; membrane bound crystals of magnetite or other
iron containing substances as iron oxide ( Fe3O4) that function as tiny magnets. Formed by several G –
bacteria to orient themselves by responding to magnetic fields.
•Bacteria that have magnetosomes can decompose H2O2 formed during cellular metabolism (protect cells).
•Industrial microbiologist develops culture methods to obtain large quantities of magnetite from bacteria.
inorganic phosphate that can be used in synthesis of ATP (characteristics of Corynebacterium diphtheriae).
•Some bacteria produce organic inclusion bodies containing either polyhydroxybutyrate or glycogen
granules for energy reserve.
•Polysaccharide inclusions consist of glycogen and starch (iodine gives reddish brown and blue color).
•Poly-ᵦ-hydroxybutyric acid is the common lipid storage material, can be detected by fat-soluble dyes
such as Sudan dyes .
•Some motile aquatic bacteria contain Magnetosomes; membrane bound crystals of magnetite or other
iron containing substances as iron oxide ( Fe3O4) that function as tiny magnets. Formed by several G –
bacteria to orient themselves by responding to magnetic fields.
•Bacteria that have magnetosomes can decompose H2O2 formed during cellular metabolism (protect cells).
•Industrial microbiologist develops culture methods to obtain large quantities of magnetite from bacteria.
Structures located outside the cell wall
•Glycocalyx: capsules and slime layers
•Flagella
•Pili
•Glycocalyx: capsules and slime layers
•Flagella
•Pili
The glycocalyx: capsules and slime layer
•All bacteria secrete some sort of glycocalyx, an outer viscous covering of fibers extending from the
bacterium.
•If appears as an extensive, tightly bound accumulation of gelatinous material adhering to the cell wall, it
is called Capsule.
•If the glycocalyx appears unorganized and more loosely attached, it is called a Slime layer.
•Composition: the glycocalyx is usually a viscous polysaccharide or poylpeptide slime, its production
depends on environmental conditions.
•All bacteria secrete some sort of glycocalyx, an outer viscous covering of fibers extending from the
bacterium.
•If appears as an extensive, tightly bound accumulation of gelatinous material adhering to the cell wall, it
is called Capsule.
•If the glycocalyx appears unorganized and more loosely attached, it is called a Slime layer.
•Composition: the glycocalyx is usually a viscous polysaccharide or poylpeptide slime, its production
depends on environmental conditions.
Capsules and slime layer
Capsule functions
•Like fimbriae, capsule, slime layer and glycocalyx often mediate adherence of cells to surfaces.
•Protect bacterial cells from engulfment by protozoa or WBCs (phagocytes).
•Protect bacterial cells from attack by antimicrobial agents of plant or animal origin.
•Protect soil bacteria from perennial effects of drying or desiccation.
•Capsular materials (e.g. Dextran) may be overproduced when bacteria fed sugars to become reserves of
carbohydrates for subsequent metabolism.
•Some bacteria produce slime materials to adhere and float themselves as colonial masses in their
environments
•Like fimbriae, capsule, slime layer and glycocalyx often mediate adherence of cells to surfaces.
•Protect bacterial cells from engulfment by protozoa or WBCs (phagocytes).
•Protect bacterial cells from attack by antimicrobial agents of plant or animal origin.
•Protect soil bacteria from perennial effects of drying or desiccation.
•Capsular materials (e.g. Dextran) may be overproduced when bacteria fed sugars to become reserves of
carbohydrates for subsequent metabolism.
•Some bacteria produce slime materials to adhere and float themselves as colonial masses in their
environments
Biofilm
•Bacteria may attach to surface, produce slime, divide and produce microcolonies within the slime layer
and construct a biofilm, which becomes an enriched and protected environment for themselves and
other bacteria.
•Ex; formation of dental plaques by the oral bacterium Streptococcus mutans.
*The bacteria adhere specifically to the pellicle of the tooth by means of a protein on the cell surface.
*Bacteria grow and synthesize a dextran capsule which binds them to the enamel and forms biofilm
300-500 cells in thickness.
*The bacteria are able to cleave sucrose (provided by animal diet) into glucose plus fructose.
*fructose is fermented as an energy source for bacterial growth.
•Bacteria may attach to surface, produce slime, divide and produce microcolonies within the slime layer
and construct a biofilm, which becomes an enriched and protected environment for themselves and
other bacteria.
•Ex; formation of dental plaques by the oral bacterium Streptococcus mutans.
*The bacteria adhere specifically to the pellicle of the tooth by means of a protein on the cell surface.
*Bacteria grow and synthesize a dextran capsule which binds them to the enamel and forms biofilm
300-500 cells in thickness.
*The bacteria are able to cleave sucrose (provided by animal diet) into glucose plus fructose.
*fructose is fermented as an energy source for bacterial growth.
•The glucose is polymerized into an extracellular dextran polymer that cements the bacteria to tooth
enamel and becomes the matrix of dental plaque.
•The dextran slime can be depolymerized to glucose for use as carbon source, resulting in production of
lactic acid within the biofilm (plaque) that decalcifies the enamel and leads to dental caries or bacterial
infection of the tooth.
Capsules may be able to protect bacterial cells from being engulfed or destroyed by phagocytes.
* The polysaccharide capsule of Streptococcus pneumoniae (primary determinant of virulence)
prevents ingestion of pneumococci by alveolar macrophages.
* Bacillus anthracis survive phagocytosis after engulfment because the lysosomal enzymes of
the phagocyte cannot initiate an attack on the polyD-glutamate capsule of the bacterium.
enamel and becomes the matrix of dental plaque.
•The dextran slime can be depolymerized to glucose for use as carbon source, resulting in production of
lactic acid within the biofilm (plaque) that decalcifies the enamel and leads to dental caries or bacterial
infection of the tooth.
Capsules may be able to protect bacterial cells from being engulfed or destroyed by phagocytes.
* The polysaccharide capsule of Streptococcus pneumoniae (primary determinant of virulence)
prevents ingestion of pneumococci by alveolar macrophages.
* Bacillus anthracis survive phagocytosis after engulfment because the lysosomal enzymes of
the phagocyte cannot initiate an attack on the polyD-glutamate capsule of the bacterium.
* Pseudomonas aeruginosa that construct a biofilm made of extracellular slime are resistant to
phagocytes, which cannot penetrate the biofilm.
phagocytes, which cannot penetrate the biofilm.
S-layer
•Composition: a regularly structured layer attached to the outermost portion of the cell wall, composed of
protein or glycoprotein.
•Found in many gram-positive and gram-negative bacteria as well as Archaea bacteria.
•Functions:
* Adhesion to host cells and environmental surfaces, colonize and resist flushing.
* May contribute to virulence by protecting bacteria against complement attack and
phagocytosis.
* protect bacteria from harmful enzymes, changes in pH and from the predatory parasitic
bacterium Bdellovibrio.
•Composition: a regularly structured layer attached to the outermost portion of the cell wall, composed of
protein or glycoprotein.
•Found in many gram-positive and gram-negative bacteria as well as Archaea bacteria.
•Functions:
* Adhesion to host cells and environmental surfaces, colonize and resist flushing.
* May contribute to virulence by protecting bacteria against complement attack and
phagocytosis.
* protect bacteria from harmful enzymes, changes in pH and from the predatory parasitic
bacterium Bdellovibrio.
Surface appendages
•Flagella
•Fimbriae
•Pili
•Flagella
•Fimbriae
•Pili
Flagella
•Filamentous protein structures
attached to the cell surface,
provide the swimming
movement for most prokaryote.
•Prokaryotic flagella are much
thinner (20 nanometers) than
eukaryotic flagellum, and they
lack the typical 9+2
arrangement of microtubules.
•Filamentous protein structures
attached to the cell surface,
provide the swimming
movement for most prokaryote.
•Prokaryotic flagella are much
thinner (20 nanometers) than
eukaryotic flagellum, and they
lack the typical 9+2
arrangement of microtubules.
•The flagellar filament is rotated by a motor apparatus in the plasma membrane allowing the cell to swim
in fluid environments.
•Bacterial flagella powered by proton motive force (chemiosmotic potential) established on the bacterial
membrane, eukaryotic flagella powered by ATP hydrolysis.
•About half of the bacilli, all of spiral and curved bacteria are motile by flagella. Few cocci are non motile,
adapted to dry environments and lack of hydrodynamic design.
in fluid environments.
•Bacterial flagella powered by proton motive force (chemiosmotic potential) established on the bacterial
membrane, eukaryotic flagella powered by ATP hydrolysis.
•About half of the bacilli, all of spiral and curved bacteria are motile by flagella. Few cocci are non motile,
adapted to dry environments and lack of hydrodynamic design.
Ultra structure of flagellum of E. coli
•Several distinct proteins.
•System of rings embedded in the cell envelope (the
basal body).
•Hook like structure near cell surface.
•Flagellar filament.
•M, S rings located in plasma membrane (motor
apparatus).
•P, L located in periplasm and the outer membrane
respectively. Function as bushings to support the rod
where it is joined to hook.
•As M ring turns by influx of protons, rotary motion
transferred to the filament which turns to propel
the bacterium.
•Several distinct proteins.
•System of rings embedded in the cell envelope (the
basal body).
•Hook like structure near cell surface.
•Flagellar filament.
•M, S rings located in plasma membrane (motor
apparatus).
•P, L located in periplasm and the outer membrane
respectively. Function as bushings to support the rod
where it is joined to hook.
•As M ring turns by influx of protons, rotary motion
transferred to the filament which turns to propel
the bacterium.
Ultra structure of flagellum of E. coli
Arrangements of bacterial flagella
•Polar; one or more flagella arising from one or
both poles of the cell.
(Monotrichous, Lophotrichous, Amphitrichous)
•Peritrichous; lateral flagella distributed over
the entire cell surface.
•Flagellar distribution is genetically distinct
trait that used to distinguish bacteria.
EX; among G – rods, Pseudomonas have polar
flagella, while enteric bacteria have
peritrichous flagella
•Polar; one or more flagella arising from one or
both poles of the cell.
(Monotrichous, Lophotrichous, Amphitrichous)
•Peritrichous; lateral flagella distributed over
the entire cell surface.
•Flagellar distribution is genetically distinct
trait that used to distinguish bacteria.
EX; among G – rods, Pseudomonas have polar
flagella, while enteric bacteria have
peritrichous flagella
Techniques used to demonstrate motility
1- flagellar stain; outline flagella and shoe their pattern of distribution
2- motility test medium; detect swimming movement on semisolid media
3- direct microscopic observation of living bacteria in a wet mount
1- flagellar stain; outline flagella and shoe their pattern of distribution
2- motility test medium; detect swimming movement on semisolid media
3- direct microscopic observation of living bacteria in a wet mount
Salmonella
typhi
flagellar stain
typhi
flagellar stain
Ecological (survival) advantages of flagella
Movement in response to environmental stimuli (Tactic response):
•Chemotaxis; a bacterium can sense the quality and quantity of certain chemicals in its
environment and swim towards them.
•Phototaxis
•Aerotaxis
•Magnetotaxis
Movement in response to environmental stimuli (Tactic response):
•Chemotaxis; a bacterium can sense the quality and quantity of certain chemicals in its
environment and swim towards them.
•Phototaxis
•Aerotaxis
•Magnetotaxis
Fimbriae
•Fimbriae and pili are interchangeable terms used to designate short, hair-like structures on the surface of
prokaryotic cells.
•Composed of protein.
•Shorter and stiffer than flagella and slightly smaller in diameter.
•Have nothing to do with bacterial movement.
•Involved in adherence of bacteria to surfaces, substrates and other cells in nature.
•Very common in G – bacteria, but occur in some archaea and G+ bacteria.
•Fimbriae and pili are interchangeable terms used to designate short, hair-like structures on the surface of
prokaryotic cells.
•Composed of protein.
•Shorter and stiffer than flagella and slightly smaller in diameter.
•Have nothing to do with bacterial movement.
•Involved in adherence of bacteria to surfaces, substrates and other cells in nature.
•Very common in G – bacteria, but occur in some archaea and G+ bacteria.
•Common pili (always called fimbriae); involved in specific adherence, they are major determinants of
bacterial virulence, they allow pathogens to attach (colonize) tissues and / or resist attack by phagocytic
WBCs.
•EX: enterotoxigenic strains of E. coli adhere to the mucosal epithelium of the intestine by means of specific
fimbriae.
•Fimbriae can occur at the poles of the bacterial cell, or they can evenly distributed over the entire surface
of the cell.
•Their number 100 – 1000 for a single bacterium (0.2 – 20 µm length).
•Fimbriation is a reversible trait and is determined by chromosomal genes, sudden mutations cause
complete and reversible loss of fimbriae
bacterial virulence, they allow pathogens to attach (colonize) tissues and / or resist attack by phagocytic
WBCs.
•EX: enterotoxigenic strains of E. coli adhere to the mucosal epithelium of the intestine by means of specific
fimbriae.
•Fimbriae can occur at the poles of the bacterial cell, or they can evenly distributed over the entire surface
of the cell.
•Their number 100 – 1000 for a single bacterium (0.2 – 20 µm length).
•Fimbriation is a reversible trait and is determined by chromosomal genes, sudden mutations cause
complete and reversible loss of fimbriae
•Fimbriae of G – bacteria can be classified according to variation of
morphology and haemoagglutinating properties:
•Type 1 (common fimbriae):
Number about 400 , about 7 nm wide and 2 µm long.
Responsible for the adhesive properties of the strain, in particular to agglutinate RBCs.
confer the ability to form pellicles on surface of static broth cultures
EX; E. coli, Salmonella and Klebsiella.
widespread among saprophytic, commensal and pathogenic bacteria
•Type 2 fimbriae:
morphologically identical to those of type 1, but differ in that they lake adhesive and
haemoagglutinating properties.
morphology and haemoagglutinating properties:
•Type 1 (common fimbriae):
Number about 400 , about 7 nm wide and 2 µm long.
Responsible for the adhesive properties of the strain, in particular to agglutinate RBCs.
confer the ability to form pellicles on surface of static broth cultures
EX; E. coli, Salmonella and Klebsiella.
widespread among saprophytic, commensal and pathogenic bacteria
•Type 2 fimbriae:
morphologically identical to those of type 1, but differ in that they lake adhesive and
haemoagglutinating properties.
•Type 3 (thin type):
restricted to Klebsiella and Serratia marcescens.
they differ from type 1 that they are thinner (4.8 nm) and more numerous.
have strong adhesion to fungal and plant cells and glass surfaces
incapable of binding to erythrocytes or animal cells, unless pretreated with tannin.
•type 4 fimbriae:
many Proteus spp produce extremely thin (4 nm)
peritrichously arranged
confer agglutinating and adhesive properties on the cells.
restricted to Klebsiella and Serratia marcescens.
they differ from type 1 that they are thinner (4.8 nm) and more numerous.
have strong adhesion to fungal and plant cells and glass surfaces
incapable of binding to erythrocytes or animal cells, unless pretreated with tannin.
•type 4 fimbriae:
many Proteus spp produce extremely thin (4 nm)
peritrichously arranged
confer agglutinating and adhesive properties on the cells.
•Fimbriae of G + bacteria:
similar to type 4 of G – bacteria.
single genus Corynebacterium.
Corynebacterium renale causes bovine pylenoephritis and cystitis.
important in adhesion and pathogenesis.
similar to type 4 of G – bacteria.
single genus Corynebacterium.
Corynebacterium renale causes bovine pylenoephritis and cystitis.
important in adhesion and pathogenesis.
Fimbriae (common pili).
Pili
•Filamentous appendages present on the surface of male (F+ & Hfr) strains of some bacteria like E. coli
and other Enterobacteria.
•Associated with the presence of plasmid.
•Only those plasmids capable of promoting chromosomal transfer contain genes for synthesis of pili.
•The Plasmids may also confer antibiotic resistance, the ability to produce bactericidal antibiotics (colicin)
or the utilization of obscure metabolites.
•A specialized type of pilus, the F or sex pili mediates the transfer of DNA between mating bacteria during
the process of conjugation.
•Filamentous appendages present on the surface of male (F+ & Hfr) strains of some bacteria like E. coli
and other Enterobacteria.
•Associated with the presence of plasmid.
•Only those plasmids capable of promoting chromosomal transfer contain genes for synthesis of pili.
•The Plasmids may also confer antibiotic resistance, the ability to produce bactericidal antibiotics (colicin)
or the utilization of obscure metabolites.
•A specialized type of pilus, the F or sex pili mediates the transfer of DNA between mating bacteria during
the process of conjugation.
Pili easily distinguished from fimbriae
•Sex pili are present in low numbers (usually between 1 and 10).
•Pili are longer and wider than the fimbriae (6 – 13 nm wide and up to 20 µm long).
•Exhibit a distinct axial hole, and often bear a terminal knob, presumably the membranal base of the
filament.
•Proteins that made up fimbriae and pili are biochemically distinct.
•Pili can absorb male phages.
•Not important in bacterial-mammalian cell interactions, but have essential role in binding bacteria
together and transfer genetic material during conjugation.
•Sex pili are present in low numbers (usually between 1 and 10).
•Pili are longer and wider than the fimbriae (6 – 13 nm wide and up to 20 µm long).
•Exhibit a distinct axial hole, and often bear a terminal knob, presumably the membranal base of the
filament.
•Proteins that made up fimbriae and pili are biochemically distinct.
•Pili can absorb male phages.
•Not important in bacterial-mammalian cell interactions, but have essential role in binding bacteria
together and transfer genetic material during conjugation.
•Bacterial cells containing conjugative plasmids are unable to transfer DNA if the plasmid contains
defective pili-specifying genes.
•Removal of pili by mechanical methods produces bacteria unable to serve as gene donors until new pili
developed.
•The attachment of antibody or specific phages to the sex pili also inhibits conjugation.
defective pili-specifying genes.
•Removal of pili by mechanical methods produces bacteria unable to serve as gene donors until new pili
developed.
•The attachment of antibody or specific phages to the sex pili also inhibits conjugation.
Pili
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