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PowerPoint to accompany
Microbiology:
A Systems Approach
Cowan/Talaro
Chapter 4
Procaryotic Profiles: The
Bacteria and Archaea
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 4
Topics
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Cell Shapes, Arrangement, and Sizes
External Structures
Cell Envelope
Internal Structures
Classification
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Relative size of a bacterial cell compared to other cells including
viruses.
Fig. 4.25 The dimension of bacteria
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Cell shapes
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Coccus
Rod or bacillus
Curved or spiral
Cell arrangements
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Scanning electron micrographs of different bacterial shapes and
arrangements.
Fig. 4.23 SEM photograph of basic shapes.
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Cellular shapes and arrangements are specific characteristics that
can be used to identify bacteria.
Fig. 4.22 Bacterial shapes and arrangements
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Some bacteria (ex. Corynebacterium) have varied shapes called
pleomorphism.
Fig. 4.24 Pleomorphism in Corynebacterium
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External Structures
• Flagella
• Pili and fimbriae
• Glycocalyx
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Flagella
• Composed of protein subunits
• Motility (chemotaxis)
• Varied arrangement (ex. Monotrichous,
lophotrichous, amphitrichous)
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Different arrangements of flagella exist for different species.
Fig. 4.3 Electron micrograph depicting types of flagella
arrangements.
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Three main parts of the flagella include the basal body, hook, and
filament.
Fig. 4.2 Details of the basal body in gram negative cell
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The rotation of the flagella enables bacteria to be motile.
Fig. 4.4 The operation of flagella and the mode of locomotion
in bacteria with polar and peritrichous flagella.
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Chemotaxis is the movement of bacteria in response to chemical
signals.
Fig. 4.5 Chemotaxis in bacteria
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Spirochete bacteria have their flagella embedded in the
membrane.
Fig. 4.6 The orientation of periplasmic flagella on the
spirochete cell.
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Pili and fimbriae
• Attachment
• Mating (Conjugation)
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Fimbriae are smaller than flagella, and are important for
attachment.
Fig. 4.7 Form and function of bacteria fimbriae
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Pili enable conjugation to occur, which is the transfer of DNA from
one bacterial cell to another.
Fig. 4.8 Three bacteria in the process of conjugating
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Glycocalyx
• Capsule
– Protects bacteria from immune cells
• Slime layer
– Enable attachment and aggregation of
bacterial cells
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The capsule is tightly bound to the cell, and is associated with
pathogenic bacteria.
Fig. 4.10 Encapsulated bacteria
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The slime layer is loosely bound to the cell.
Fig. 4.9 Bacterial
cells sectioned to
show the types
of glycocalyces.
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The slime layer is associated with the formation of biofilms, which
are typically found on teeth.
Fig. 4.11 Biofilm
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Cell envelope
• Cell wall
– Gram-positive
– Gram-negative
• Cytoplasmic membrane
• Non cell wall
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Cell wall
• Gram positive cell wall
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Thick peptidoglycan (PG) layer
Teichoic acid and lipoteichoic acid
Acidic polysaccharides
Lipids – mycolic acids - Mycobacteria
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Thin PG layer
Outer membrane
Lipid polysaccharide
Porins
• Gram-negative cell wall
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PG is a complex sugar and peptide structure important for cell
wall stability and shape.
Fig. 4.13 Structure of peptidoglycan in the cell wall
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Structures associated with gram-positive and gram-negative cell
walls.
Fig. 4.14 A comparison of the detailed structure of
gram-positive and gram-negative cell walls.
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Mutations can cause some bacteria to lose the ability to
synthesize the cell wall, and are called L forms.
Fig. 4.16 The conversion of walled bacterial cells to L forms
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No cell wall
• No PG layer
• Cell membrane contain sterols for
stability
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Mycoplasma bacteria have no cell wall, which contributes to
varied shapes.
Fig. 4.15 Scanning electron micrograph of Mycoplasma
pneumoniae
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Cytoplasmic membrane
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Fluid-Mosaic Model
Phospholipids
Embedded proteins
Energy generation
Selective barrier; semipermeable
Transport
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Internal Structures
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Cytoplasm
Genetic structures
Storage bodies
Actin
Endospore
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Cytoplasm
• Area inside the membrane
• About 80% water
• Gelatinous solution containing water,
nutrients, proteins, and genetic material.
• Site for cell metabolism
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Genetic structures
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Single, circular chromosome
Nucleoid region
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
Plasmids
Ribosomes
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Most bacteria contain a single circular double strand of DNA
called a chromosome.
Fig. 4.17 Chromosome structure
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A ribosome is a combination of RNA and protein, and is involved
in protein synthesis.
Fig. 4.18 A model of a procaryotic ribosome.
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Inclusion bodies enable a cell to store nutrients, and to survive
nutrient depleted environments.
Fig. 4.19 An example of a storage inclusion
in a bacterial cell.
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Actin is a protein fiber (cytoskeleton) present in some bacteria,
and is involved in maintaining cell shape.
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Fig. 4.20 Bacterial cytoskeleton
During nutrient depleted conditions, some bacteria (vegetative
cell) form into an endospore in order to survive.
Fig. 4.21 Microscopic picture of an endospore formation
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Some pathogenic bacteria that produce toxins during the
vegetative stage are capable of forming spores.
Table 4.1 General stages in endospore formation
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Classification
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Phenotypic methods
Molecular methods
Taxonomic scheme
Unique groups
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Phenotypic methods
• Cell morphology -staining
• Biochemical test – enzyme test
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Molecular methods
• DNA sequence
• 16S RNA
• Protein sequence
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The methods of classification have allowed bacteria to be grouped
into different divisions and classes.
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Table 4.3 Major taxonomic groups of bacteria
An example of how medically important families and genera of
bacterial are characterized.
Table 4.4 Medically important families and genera of bacteria.
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Unique groups of bacteria
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Intracellular parasites
Photosynthetic bacteria
Green and purple sulfur bacteria
Gliding and fruiting bacteria
Archaea bacteria
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Intracellular bacteria must live in host cells in order to undergo
metabolism and reproduction.
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Fig. 4.26 Transmission electron micrograph of rickettsia.
Cyanobacteria are important photosynthetic bacteria associated
with oxygen production.
Fig. 4.27 Structure and examples of cyanobacteria
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Green and purple sulfur bacteria are photosynthetic, do not give
off oxygen, and are found in sulfur springs, freshwater, and
swamps.
Fig. 4.28 Behavior of purple sulfur bacteria
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An example of a fruiting body bacteria in which reproductive
spores are produced.
Fig. 4.29 Myxobacterium
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Archaea bacteria
• Associated with extreme environments
• Contain unique cell walls
• Contain unique internal structures
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Archaea bacteria that survive are found in hot springs
(thermophiles) and high salt content areas (halophiles).
Fig. 4.30 Halophile
around the world
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