Figure 3.18 Peptidoglycan cable Ribitol Wall-associated protein Teichoic acid Peptidoglycan...

Figure 3.18

Peptidoglycancable

Ribitol

Wall-associatedprotein

Teichoic acid Peptidoglycan

Lipoteichoicacid

Cytoplasmic membrane

© 2012 Pearson Education, Inc.

3.6 The Cell Wall of Bacteria: Peptidoglycan

• Prokaryotes That Lack Cell Walls– Mycoplasmas

• Group of pathogenic bacteria

– Thermoplasma• Species of Archaea


3.7 The Outer Membrane

• Total cell wall contains ~10% peptidoglycan (Figure 3.20a)

• Most of cell wall composed of outer membrane (aka lipopolysaccharide [LPS] layer)

– LPS consists of core polysaccharide and O-polysaccharide

– LPS replaces most of phospholipids in outer half of outer membrane

– Endotoxin: the toxic component of LPS


Figure 3.20a

O-polysaccharide

Peptidoglycan

Core polysaccharide

Lipid A Protein

Porin

Out

8 nm

Phospholipid

Lipopolysaccharide(LPS)

Lipoprotein

In

Outermembrane

Periplasm

Cytoplasmic membrane

Cellwall


3.7 The Outer Membrane

• Porins: channels for movement of hydrophilic low-molecular weight substances (Figure 3.20b)

• Periplasm: space located between cytoplasmic and outer membranes

– ~15 nm wide

– Contents have gel-like consistency

– Houses many proteins


3.8 Cell Walls of Archaea

• No peptidoglycan• Typically no outer membrane• Pseudomurein

– Polysaccharide similar to peptidoglycan (Figure 3.21)

– Composed of N-acetylglucosamine and N-acetyltalosaminuronic acid

– Found in cell walls of certain methanogenic Archaea

• Cell walls of some Archaea lack pseudomurein


Figure 3.21

Lysozyme-insensitive

N-Acetylglucosamine

N-Acetyltalosaminuronicacid

N-Acetyl group

Peptidecross-links


3.8 Cell Walls of Archaea

• S-Layers– Most common cell wall type among Archaea

– Consist of protein or glycoprotein

– Paracrystalline structure (Figure 3.22)


Figure 3.22


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

Cell Capsule



• Fimbriae– Filamentous protein structures (Figure 3.24)

– Enable organisms to stick to surfaces or form pellicles


Figure 3.24

Flagella

Fimbriae



• 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 twitching motility


Figure 3.25

Virus-coveredpilus


Figure 3.26

-carbon

Polyhydroxyalkanoate


Figure 3.27

Polyphosphate

Sulfur


Figure 3.28


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


Figure 3.31Ribs

GvpA

GvpC


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

Terminalspores

Subterminalspores

Centralspores


Figure 3.33

Vegetative cell

Developing spore

Sporulating cell

Mature spore


3.12 Endospores

• Endospore Structure (Figure 3.35)– Structurally complex

– Contains dipicolinic acid

– Enriched in Ca2+

– Core contains small acid-soluble proteins (SASPs)


Figure 3.35

Exosporium

Spore coat

Core wall

Cortex

DNA


3.12 Endospores

• The Sporulation Process– Complex series of events (Figure 3.37)

– Genetically directed


Figure 3.37

Free endospore

Stage VI, VIIStage V

Coat

Stage IV

Stage IIIStage II

Mother cell

Prespore

Septum

Sporulation stages

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


3.13 Flagella and Motility

• Flagellum (pl. flagella): structure that assists in swimming

– Different arrangements: peritrichous, polar, lophotrichous (Figure 3.38)

– Helical in shape

Animation: The Prokaryotic FlagellumAnimation: The Prokaryotic Flagellum


Figure 3.38



• Flagellar Structure– Consists of several components (Figure 3.41)

– Filament composed of flagellin

– Move by rotation


Figure 3.41

Rod

C Ring

MS Ring

Motprotein

Mot proteinMot protein Fli proteins(motor switch)

45 nm

Cytoplasmicmembrane

Basalbody

Rod

C Ring

MS Ring

P Ring

Periplasm Peptidoglycan

L Ring

HookOutermembrane(LPS)

Flagellin

Filament

MS

LP

15—20 nm



• Flagella increase or decrease rotational speed in relation to strength of the proton motive force

• Differences in swimming motions (Figure 3.44)– Peritrichously flagellated cells move slowly in a

straight line

– Polarly flagellated cells move more rapidly and typically spin around


Figure 3.44

Polar

Peritrichous

CW rotation

CCW rotation

Unidirectional flagella

Cellstops,reorients

Reversible flagella

Bundledflagella(CCW rotation)

Tumble—flagellapushed apart(CW rotation)

Flagella bundled(CCW rotation)

CW rotation

CW rotation


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


Figure 3.47

No attractant present:Random movement

Attractant present:Directed movement

Tumble

Run

Tumble

Run

Attractant



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


Figure 3.48

Time

Repellent

Control

Attractant

Repellent

Control Attractant

Cel

ls p

er t

ub

e


Figure 3.18 Peptidoglycan cable Ribitol Wall-associated protein Teichoic acid Peptidoglycan...

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