michael t. madigan, john m. martinko, david a. stahl...

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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

Lectures by

John Zamora

Middle Tennessee State University

© 2012 Pearson Education, Inc.

Cell Structure and Function in Bacteria

and Archaea

Chapter 3

I. Cell Shape and Size

• 3.1 Cell Morphology

• 3.2 Cell Size and the Significance of

Smallness

© 2012 Pearson Education, Inc. Marmara University – Enve303 Env. Eng. Microbiology – Prof. BARIŞ ÇALLI

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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


Figure 3.1 Representative cell morphologies of prokaryotes

Coccus

Rod

Spirillum

Spirochete

Stalk

Hypha

Budding and

appendaged bacteria

Filamentous bacteria


Coccus cells may also exist as short chains

or grapelike clusters

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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 functions and activities of living organisms and their parts

2 the evolutionary history of a group of organisms

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


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 = 2 m

r = 1 m

r = 2 m

Surface area (4r2) = 12.6 m2

Volume ( r3) = 4.2 m3

Surface area = 50.3 m2

Volume = 33.5 m3

3 4

Surface Volume

= 3

Surface Volume

= 1.5



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


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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• 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

3.3 The Cytoplasmic Membrane

Animation: Membrane Structure


Fatty acids

Glycerol

Phosphate

Ethanolamine

Fatty acids

Glycerophosphates

Hydrophilic

region

region

region

Hydrophobic

Hydrophilic

Fatty acids


General architecture

of a bilayer

membrane; the blue

balls depict glycerol

with phosphate and

(or) other hydrophilic

groups.

Figure 3.4 Phospholipid bilayer membrane

membrane_structure.html

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• 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


Figure 3.5 Structure of the cytoplasmic membrane

Phospholipids

Integral

membrane

proteins

6–8 nm

Hydrophilic

groups

groups

Hydrophobic

Out

In

Phospholipid

molecule


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• 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



• 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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• 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



• 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)

Lipid bilayer

In

Out

Membrane protein

Glycerophosphates

Phytanyl


Out

In

Lipid monolayer

Biphytanyl

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: Prevents leakage and functions as a gateway for transport of nutrients into, and wastes out of, the cell

Protein anchor: Site of many proteins that participate in transport, bioenergetics, and chemotaxis

Energy conservation: Site of generation and use of the proton motive force


Although structurally weak, the cytoplasmic membrane has many

important cellular functions.

3.5 Transport and Transport Systems

• Carrier-Mediated Transport Systems (Figure 3.9)

– Show saturation effect

– Highly specific


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Figure 3.9 Transport versus diffusion.

Rate

of

so

lute

en

try

Transporter saturated

with substrate

Transport

Simple diffusion

External concentration of solute


In transport, the

uptake rate

shows saturation

at relatively low

external

concentrations

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

Uniporter Antiporter Symporter

Out

In


Membrane-

spanning

transporters are

made of 12 α-

helices (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.

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)


Figure 3.16 Cell walls of Bacteria. (a, b) Schematic diagrams of gram-positive and gram-negative cell

walls.


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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


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


Figure 3.20a The gram-negative cell wall. Arrangement of lipopolysaccharide, lipid A, phospholipid,

porins, and lipoprotein in the outer membrane


O-polysaccharide

Peptidoglycan

Core polysaccharide

Lipid A Protein

Porin

Out

8 nm

Phospholipid

Lipopolysaccharide

(LPS)

Lipoprotein

In

Outermembrane

Periplasm

Cytoplasmic

membrane

Cellwall

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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 N-

acetyltalosaminuronic acid

– Found in cell walls of certain methanogenic

Archaea

• Cell walls of some Archaea lack pseudomurein


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


Figure 3.23

Bacterial capsules.

Cell Capsule


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.

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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• Fimbriae

– Filamentous protein structures (Figure 3.24)

– Enable organisms to stick to surfaces or form

pellicles (film)


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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• 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


Figure 3.25 Pili

Virus- covered 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)


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


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


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.

3.12 Endospores

• Endospore Structure (Figure 3.35)

– Structurally complex

– Contains dipicolinic acid

– Enriched in Ca2+

– Core contains small acid-

soluble proteins (SASPs)


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3.12 Endospores

• The Sporulation Process

– Complex series of events (Figure 3.37)

– Genetically directed


Figure 3.37 Stages in endospore formation.


Stages are defined from genetic and microscopic analyses of sporulation in

Bacillus subtilis, the model organism for studies of sporulation.

Free endospore

Stage VI, VIIStage V

Coat

Stage IV

Stage IIIStage II

Mother cell

Prespore

Septum

Sporulationstages

Cortex

Cell wall

Cytoplasmicmembrane

Vegetative cycle

Maturation,cell lysis

Celldivision

GerminationGrowth

Engulfment

Asymmetriccell division;commitmentto sporulation,Stage I

Spore coat, Ca2

uptake, SASPs,dipicolinic acid

Cortexformation

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V. Microbial Locomotion

• 3.13 Flagella and Motility

• 3.14 Gliding Motility

• 3.15 Microbial Taxes


3.13 Flagella and Motility

• Flagellum (pl. flagella): structure that assists

in swimming

– Different arrangements: peritrichous, polar,

lophotrichous

– Helical in shape


Animation: Flagella Arrangement

flagella_arrangement.html

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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


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



• 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

Run

Tumble

Run

Attractant


No attractant present:

Random movement. In the

absence of a chemical

attractant the cell swims

randomly in runs, changing

direction during tumbles.

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.


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.

(c) Accumulation of bacteria in a capillary

containing an attractant.

(d) Repulsion of bacteria by a repellent.

Time course showing cell

numbers in capillaries

containing various chemicals.

michael t. madigan, john m. martinko, david a. stahl...

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