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LECTURE PRESENTATIONS
For BROCK BIOLOGY OF MICROORGANISMS, THIRTEENTH EDITION
Michael T. Madigan, John M. Martinko, David A. Stahl, David P. Clark
Chapter 3
Lectures by
John Zamora
Middle Tennessee State University
Cell Structure and
Function in Bacteria
and Archaea
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I. Cell Shape and Size
• 3.1 Cell Morphology
• 3.2 Cell Size and the Significance of
Smallness
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3.1 Cell Morphology
• Morphology = cell shape
• Major cell morphologies (Figure 3.1)
– Coccus (pl. cocci): spherical or ovoid
– Rod: cylindrical shape
– Spirillum: spiral shape
• Cells with unusual shapes
– Spirochetes, appendaged bacteria, and
filamentous bacteria
• Many variations on basic morphological types
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Figure 3.1 Representative cell morphologies of prokaryotes
Spirochete
Coccus
Coccus cells may also exist as short chains
or grapelike clusters
Stalk
Rod
Hypha
Budding and
appendaged bacteria
Spirillum
Filamentous bacteria
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3.1 Cell Morphology
• Morphology typically does not predict physiology1,
ecology, phylogeny2, etc. of a prokaryotic cell
• Selective forces may be involved in setting the
morphology
– Optimization for nutrient uptake (small cells and
those with high surface-to-volume ratio)
– Swimming motility in viscous environments or
near surfaces (helical or spiral-shaped cells)
– Gliding motility (filamentous bacteria)
1
2
functions and activities of living organisms and their parts
the evolutionary history of a group of organisms
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3.2 Cell Size and the Significance of
Smallness
• Size range for prokaryotes: 0.2 µm to >700 µm in
diameter
– Most cultured rod-shaped bacteria are between
0.5 and 4.0 µm wide and <15 µm long
– Examples of very large prokaryotes
• Epulopiscium fishelsoni (Figure 3.2a)
• Thiomargarita namibiensis (Figure 3.2b)
• Size range for eukaryotic cells: 10 to >200 µm in
diameter
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Figure 3.2 Some very large prokaryotes
Epulopiscium fishelsoni
Thiomargarita namibiensis
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3.2 Cell Size and the Significance of
Smallness
• Surface-to-Volume Ratios, Growth Rates, and
Evolution
– Advantages to being small (Figure 3.3)
• Small cells have more surface area relative to cell
volume than large cells (i.e., higher S/V)
– support greater nutrient exchange per unit cell
volume
– tend to grow faster than larger cells
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Figure 3.3 Surface area and volume relationships in cells
r = 1 m
r = 1 m
Surface area (4r2) = 12.6 m2
4
Volume ( 3 r3) = 4.2 m3
Surface
=3
Volume
r = 2 m
r = 2 m
Surface area = 50.3 m2
Volume = 33.5 m3
Surface
= 1.5
Volume
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3.2 Cell Size and the Significance of
Smallness
• Lower Limits of Cell Size
– Cellular organisms <0.15 µm in diameter are
unlikely
– Open oceans tend to contain small cells (0.2–
0.4 µm in diameter)
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II. The Cytoplasmic Membrane and
Transport
• 3.3 The Cytoplasmic Membrane
• 3.4 Functions of the Cytoplasmic Membrane
• 3.5 Transport and Transport Systems
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3.3 The Cytoplasmic Membrane in
Bacteria and Archaea
• Cytoplasmic membrane:
– Thin structure that surrounds the cell
– 6-8 nm thick
– Vital barrier that separates cytoplasm from
environment
– Highly selective permeable barrier; enables
concentration of specific metabolites and
excretion of waste products
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3.3 The Cytoplasmic Membrane
• Composition of Membranes
– General structure is phospholipid bilayer
(Figure 3.4)
• Contain both hydrophobic and hydrophilic
components
– Can exist in many different chemical forms as a
result of variation in the groups attached to the
glycerol backbone
– Fatty acids point inward to form hydrophobic
environment; hydrophilic portions remain exposed
to external environment or the cytoplasm
Animation: Membrane Structure
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Figure 3.4 Phospholipid bilayer membrane
Glycerol
Fatty acids
Phosphate
Ethanolamine
Hydrophilic General architecture
region
of a bilayer
membrane; the blue
Fatty acids
Hydrophobic
balls depict glycerol
region
with phosphate and
Hydrophilic (or) other hydrophilic
region
groups.
Glycerophosphates
Fatty acids
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3.3 The Cytoplasmic Membrane
• Cytoplasmic Membrane (Figure 3.5)
– 6-8 nm wide
– Embedded proteins
– Stabilized by hydrogen bonds and hydrophobic
interactions
– Mg2+ and Ca2+ help stabilize membrane by forming
ionic bonds with negative charges on the
phospholipids
– Somewhat fluid
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Figure 3.5 Structure of the cytoplasmic membrane
Out
Phospholipids
Hydrophilic
groups
6–8 nm
Hydrophobic
groups
In
Integral
membrane
proteins
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Phospholipid
molecule
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3.3 The Cytoplasmic Membrane
• Membrane Proteins
– Outer surface of cytoplasmic membrane can
interact with a variety of proteins that bind
substrates or process large molecules for transport
– Inner surface of cytoplasmic membrane interacts
with proteins involved in energy-yielding reactions
and other important cellular functions
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3.3 The Cytoplasmic Membrane
• Membrane Proteins (cont’d)
– Integral membrane proteins
• Firmly embedded in the membrane
– Peripheral membrane proteins
• One portion anchored in the membrane
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3.3 The Cytoplasmic Membrane
• Membrane-Strengthening Agents
– Sterols
• Rigid, planar lipids found in eukaryotic membranes
Strengthen and stabilize membranes
– Hopanoids
• Structurally similar to sterols
• Present in membranes of many Bacteria
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3.3 The Cytoplasmic Membrane
• Archaeal Membranes
– Ether linkages in phospholipids of Archaea
– Bacteria and Eukarya that have ester linkages in
phospholipids
– Can exist as lipid monolayers, bilayers, or mixture
(Figure 3.7d and e)
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Figure 3.7d,e Membrane structure in Archaea may be bilayer or monolayer (or a mix of both)
Out
Glycerophosphates
Phytanyl
Membrane protein
In
Out
Lipid bilayer
Biphytanyl
In
Lipid monolayer
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3.4 Functions of the Cytoplasmic
Membrane (Figure 3.8)
• Permeability Barrier
– Polar and charged molecules must be
transported
– Transport proteins accumulate solutes against
the concentration gradient
• Protein Anchor
– Holds transport proteins in place
• Energy Conservation
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Figure 3.8 The major functions of the cytoplasmic membrane.
Permeability barrier:
Protein anchor:
Energy conservation:
Prevents leakage and functions
as a gateway for transport of
nutrients into, and wastes out
of, the cell
Site of many proteins that
participate in transport,
bioenergetics, and chemotaxis
Site of generation and use of the
proton motive force
Although structurally weak, the cytoplasmic membrane has many
important cellular functions.
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3.5 Transport and Transport Systems
• Carrier-Mediated Transport Systems (Figure 3.9)
– Show saturation effect
– Highly specific
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Rate of solute entry
Figure 3.9 Transport versus diffusion.
Transporter saturated
with substrate
Transport
In transport, the
uptake rate
shows saturation
at relatively low
external
concentrations
Simple diffusion
External concentration of solute
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3.5 Transport and Transport Systems
• Three transport events are possible: uniport,
symport, and antiport (Figure 3.11)
– Uniporters transport in one direction across the
membrane
– Symporters function as co-transporters
– Antiporters transport a molecule across the
membrane while simultaneously transporting
another molecule in the opposite direction
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Figure 3.11 Structure of membrane-spanning transporters and types of transport events
Out
In
Uniporter
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Antiporter
Symporter
Membranespanning
transporters are
made of 12 αhelices (each
shown here as a
cylinder) that
aggregate to form a
channel through the
membrane. Shown
here are three
different transport
events; for
antiporters and
symporters, the
cotransported
substance is
shown in yellow.
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III. Cell Walls of Prokaryotes
• 3.6 The Cell Wall of Bacteria: Peptidoglycan
• 3.7 The Outer Membrane
• 3.8 Cell Walls of Archaea
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3.6 The Cell Wall of Bacteria:
Peptidoglycan
Peptidoglycan (Figure 3.16)
– Rigid layer that provides strength to cell wall
– Polysaccharide composed of
•
•
•
•
N-acetylglucosamine and N-acetylmuramic acid
Amino acids
Lysine or diaminopimelic acid (DAP)
Cross-linked differently in gram-negative bacteria
and gram-positive bacteria (Figure 3.17)
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Figure 3.16 Cell walls of Bacteria. (a, b) Schematic diagrams of gram-positive and gram-negative cell
walls.
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3.6 The Cell Wall of Bacteria:
Peptidoglycan
• Gram-Positive Cell Walls (Figure 3.18)
– Can contain up to 90%
peptidoglycan
– Common to have
teichoic acids (acidic
substances) embedded
in the cell wall
• Lipoteichoic acids:
teichoic acids
covalently bound to
membrane lipids
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3.6 The Cell Wall of Bacteria:
Peptidoglycan
• Prokaryotes That Lack Cell Walls
– Mycoplasmas
• Group of pathogenic bacteria
– Thermoplasma
• Species of Archaea
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3.7 The Outer Membrane
• Total cell wall contains ~10% peptidoglycan
(Figure 3.20a)
• Most of cell wall composed of outer membrane
(lipopolysaccharide [LPS] layer)
• Structural differences between cell walls of
gram-positive and gram-negative Bacteria are
responsible for differences in the Gram stain
reaction
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Figure 3.20a The gram-negative cell wall. Arrangement of lipopolysaccharide, lipid A, phospholipid,
porins, and lipoprotein in the outer membrane
O-polysaccharide
Core polysaccharide
Lipid A
Protein
Out
Lipopolysaccharide
(LPS)
Porin
Cell
wall
8 nm
Outer
membrane
Periplasm
Peptidoglycan
Phospholipid
Lipoprotein
Cytoplasmic
membrane
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In
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3.8 Cell Walls of Archaea
• No peptidoglycan
• Typically no outer membrane
• Pseudomurein
– Polysaccharide similar to peptidoglycan
Composed of N-acetylglucosamine and Nacetyltalosaminuronic acid
– Found in cell walls of certain methanogenic
Archaea
• Cell walls of some Archaea lack pseudomurein
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IV. Other Cell Surface Structures and
Inclusions
•
•
•
•
3.9 Cell Surface Structures
3.10 Cell Inclusions
3.11 Gas Vesicles
3.12 Endospores
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3.9 Cell Surface Structures
• Capsules and Slime Layers
– Polysaccharide layers (Figure 3.23)
• May be thick or thin, rigid or flexible
– Assist in attachment to surfaces
– Protect against phagocytosis
– Resist desiccation
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Figure 3.23
Bacterial capsules.
Capsules of Acinetobacter species
observed by phase-contrast
microscopy after negative staining of
cells with India ink. India ink does not
penetrate the capsule, so the capsule
appears as a light area surrounding
the cell, which appears black.
Transmission electron micrograph of
a thin section of cells of
Rhodobacter capsulatus with
capsules (arrows) clearly evident;
cells are about 0.9 µm wide.
Cell Capsule
Transmission electron micrograph of
Rhizobium trifolii stained with
ruthenium red to reveal the capsule.
The cell is about 0.7 µm wide.
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3.9 Cell Surface Structures
• Fimbriae
– Filamentous protein structures (Figure 3.24)
– Enable organisms to stick to surfaces or form
pellicles (film)
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Figure 3.24 Fimbriae
Flagella
Fimbriae
Electron micrograph of a dividing cell of Salmonella typhi, showing
flagella and fimbriae. A single cell is about 0.9 µm wide.
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3.9 Cell Surface Structures
• Pili
–
–
–
–
Filamentous protein structures (Figure 3.25)
Typically longer than fimbriae
Assist in surface attachment
Facilitate genetic exchange between cells
(conjugation)
– Type IV pili involved in motility
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Figure 3.25 Pili
Viruscovered
pilus
The pilus on an Escherichia coli cell that is undergoing conjugation (a
form of genetic transfer) with a second cell is better resolved because
viruses have adhered to it. The cells are about 0.8 m wide.
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3.10 Cell Inclusions
• Carbon storage polymers
– Poly--hydroxybutyric acid (PHB): lipid (Figure
3.26)
– Glycogen: glucose polymer
• Polyphosphates: accumulations of inorganic
phosphate (Figure 3.27)
• Sulfur globules: composed of elemental sulfur
• Magnetosomes: magnetic storage inclusions
(Figure 3.28)
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Figure 3.26 Poly-β-hydroxyalkanoates.
Polyhydroxyalkanoate
Electron micrograph of a thin section of cells of a bacterium containing
granules of PHA. Nile red–stained cells of a PHA-containing bacterium.
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3.11 Gas Vesicles
• Gas Vesicles
– Confer buoyancy in planktonic cells
(Figure 3.29)
– Spindle-shaped, gas-filled structures made of
protein (Figure 3.30)
– Gas vesicle impermeable to water
– Molecular Structure of Gas Vesicles
• Gas vesicles are composed of two proteins:
GvpA and GvpC
• Function by decreasing cell density
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Figure 3.29 Buoyant cyanobacteria.
Flotation of gas-vesiculate cyanobacteria that formed a bloom in a
freshwater lake, Lake Mendota, Madison, Wisconsin (USA).
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3.12 Endospores
• Endospores
– Highly differentiated cells resistant to heat, harsh
chemicals, and radiation (Figure 3.32)
– “Dormant” stage of bacterial life cycle
(Figure 3.33)
– Ideal for dispersal via wind, water, or animal gut
– Only present in some gram-positive bacteria
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Figure 3.32 The bacterial endospore.
Terminal
spores
Subterminal
spores
Central
spores
Phase-contrast photomicrographs illustrating endospore morphologies
and intracellular locations in different species of endospore-forming
bacteria. Endospores appear bright by phase-contrast microscopy.
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Figure 3.33 The life cycle of an endospore-forming bacterium.
Vegetative cell
Developing spore
Sporulating cell
Mature spore
The phase-contrast photomicrographs are of cells of Clostridium pascui.
A cell is about 0.8 m wide.
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3.12 Endospores
• Endospore Structure (Figure 3.35)
–
–
–
–
Structurally complex
Contains dipicolinic acid
Enriched in Ca2+
Core contains small acidsoluble proteins (SASPs)
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3.12 Endospores
• The Sporulation Process
– Complex series of events (Figure 3.37)
– Genetically directed
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Figure 3.37 Stages in endospore formation.
Coat
Growth
Spore coat, Ca2
uptake, SASPs,
dipicolinic acid
Maturation,
cell lysis
Free endospore
Stage VI, VII
Germination
Stage V
Cortex
Sporulation
stages
Vegetative
cycle
Cell
division
Cell wall
Cytoplasmic
membrane
Asymmetric
cell division;
commitment
to sporulation,
Stage I
Cortex
formation
Stage IV
Prespore
Septum
Engulfment
Mother cell
Stage II
Stage III
Stages are defined from genetic and microscopic analyses of sporulation in
Bacillus subtilis, the model organism for studies of sporulation.
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V. Microbial Locomotion
• 3.13 Flagella and Motility
• 3.14 Gliding Motility
• 3.15 Microbial Taxes
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3.13 Flagella and Motility
• Flagellum (pl. flagella): structure that assists
in swimming
– Different arrangements: peritrichous, polar,
lophotrichous
– Helical in shape
Animation: Flagella Arrangement
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3.13 Flagella and Motility
• Flagella increase or decrease rotational speed in
relation to strength of the proton motive force
• Differences in swimming motions
– Peritrichously flagellated cells move slowly in a
straight line
– Polarly flagellated cells move more rapidly and
typically spin around
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3.14 Gliding Motility
• Gliding Motility
–
–
–
–
–
Flagella-independent motility
Slower and smoother than swimming
Movement typically occurs along long axis of cell
Requires surface contact
Mechanisms
• Excretion of polysaccharide slime
• Type IV pili
• Gliding-specific proteins
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3.15 Microbial Taxes
• Taxis: directed movement in response to chemical
or physical gradients
–
–
–
–
–
Chemotaxis: response to chemicals
Phototaxis: response to light
Aerotaxis: response to oxygen
Osmotaxis: response to ionic strength
Hydrotaxis: response to water
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3.15 Microbial Taxes
• Chemotaxis
– Best studied in E. coli
– Bacteria respond to temporal, not spatial,
difference in chemical concentration
– “Run and tumble” behavior (Figure 3.47)
– Attractants and receptors sensed by
chemoreceptors
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Figure 3.47 Chemotaxis in a peritrichously flagellated bacterium such as Escherichia coli.
Tumble
Attractant
Tumble
Run
Run
No attractant present:
Random movement. In the
absence of a chemical
attractant the cell swims
randomly in runs, changing
direction during tumbles.
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Attractant present: Directed movement
In the presence of an attractant runs
become biased, and the cell moves up the
gradient of the attractant. The attractant
gradient is depicted in green, with the
highest concentration where the color is
most intense.
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3.15 Microbial Taxes
 Measuring Chemotaxis (Figure 3.48)
 Measured by inserting a capillary tube
containing an attractant or a repellent in a
medium of motile bacteria
 Can also be seen under a microscope
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Figure 3.48 Measuring chemotaxis using a capillary tube assay.
(a) Insertion of the capillary into a bacterial
suspension. As the capillary is inserted,
a gradient of the chemical begins to
form.
(b) Control capillary contains a salt solution
that is neither an attractant nor a
repellent. Cell concentration inside the
capillary becomes the same as that
outside.
Time course showing cell
(c) Accumulation of bacteria in a capillary
numbers in capillaries
containing an attractant.
containing various chemicals.
(d) Repulsion of bacteria by a repellent.
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