PowerPoint to accompany

Foundations in Microbiology
Fifth Edition

Talaro
Chapter
4
2
OVERVIEW

-All organisms are composed of cells

-Cells carry out fundamental activities (growth, reproduction,
synthesis, transport)
-Procaryotic cells – simplest, most abundant organisms on earth
-Representative procaryotes: bacteria and archaea (lack nucleus, but
functionally complex)
-Structure of bacterial cells is compact and capable of adaptations to a
multitude of habitats
-The cell is encased in an envelope that protects, supports and
regulates transport
OVERVIEW

-Bacteria have special structures for motility and adhesion in the

environment
-Bacterial cells contain genetic material in one or a few
chromosomes, and ribosomes for synthesizing proteins
- bacteria have the capacity for reproduction, nutrient storage,
dormancy and resistance to adverse conditions
-Shape, size and arrangement of bacterial cells are extremely varied
-Bacterial taxonomy and classification is based on their structure,
metabolism and genetics
-Archaea are procaryotic cells that often live in extreme environments
and possess unique biochemistry and genetics
 Characteristics of Cells and Life
- Unicellular vs multicellular organisms
Common characteristics of cells:
1. Basic shapes (spherical, cubical, cylindrical)
2. Cytoplasm always surrounded by a membrane
3. Have chromosomes containing DNA and ribosomes
capable of performing highly complex chemical
reactions
4. Most cells types fall into two different lines:
procaryotic (bacteria and archaea) and eucaryotic
cells (plants, fungi, animals, protists)
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Characteristics most inherent to life:
1. Growth and development
2. Reproduction and heredity
3. Metabolism
4. Movement and/or irritability
5. Cell support, protection and storage
mechanisms
6. The capacity to transport substances into
and out of the cell

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 Heredity and Reproduction
• Genome – complete set of genetic
information where hereditary material of an
organism lies
– Composed of elongate strands of DNA packed
into discrete bodies called chromosomes
– Eucaryotic cells: chromosomes inside a nuclear
membrane
– Procaryotic cells: DNA in a special type of
circular chromosome not enclosed by a
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membrane
 Heredity and Reproduction
• Reproduction – necessary for perpetuation
of species
• Sexual reproduction - most eucaryotes
• Asexual reproduction – eucaryotes and
procaryotes
• Binary fission – basic reproductive process
of procaryotes where a cell splits into two

8
 Metabolism: Chemical and Physical
Life Processes
Organelle/ activity procaryote Eucaryote

ribosomes scattered in the dispersed throughout

cytoplasm the cell/inserted into
ER
Generation of energy In the cell membrane In mitochondria

photosynthesis Trap energy by Has chloroplasts that

means of pigments contain the pigments
and convert it into for photosynthesis
chemical energy in
the cell but without
chloroplasts
10
 Irritability
• the capacity to respond to chemical, mechanical or
light stimuli
• For adaptation to a changing environment and
obtain nutrients
• True motility (self-propulsion)
Appendage for movement
Eucaryote Flagella, pseudopods
Procaryote Flagella (unique to bacteria), special fibrils that
produce a gliding motility
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 Protection and Storage
• Presence of cell walls that differ in
composition
• Microbes store nutrients inside cells as
buffer against depleted resources
• Eucaryotes store nutrients in membranous
packets (vacuoles); procaryotes concentrate
them in crystal form (granules or inclusions)

12
 Transport: Movement of Nutrient and
Wastes
• Cell survival depends on drawing nutrients from
the external environment and expelling waste
and other metabolic products from the internal
environment
• Two-directional transport similar in eucarytoes
and procaryotes achieved by the cell membrane
• Eucaryotes: additional organelle: golgi
apparatus that assists in sorting and packaging
molecules for transtport and removal from the
cell 13
 Prokaryotic Profiles:
the Bacteria and the Archaea
• Very first cells to appear on earth: archaea related
to modern forms that live on sulfur compounds in
geothermal ocean vents
• Has versatile and adaptable cell structure and
function

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Generalized Structure of a Procaryotic cell:

1. External 🡪 Appendages: flagella, pili, fimbriae / 🡪

Glycocalyx: capsule, slime layer)
2. Cell envelope 🡪 Cell Wall, Cell Membrane*
3. Internal 🡪 cytoplasmic matrix*, ribosomes*, inclusions,
nucleoid/chromosome*, actin cytoskeleton, endospore

* - structures essential to function of all procaryotic cells

- Majority has cell wall, and some form of surface coating
or glycocalyx
- Others are specific structures found in some, but not all
bacteria
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Fig. 4.1
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Cell Envelope: The Boundary Layer of Bacteria
(Cell Wall & Cell Membrane)

Differences in Cell Envelope Structure

- Gram stain – a staining technique that delineates

two generally different groups of bacteria
- Developed by Hans Christian Gram (1884)

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Gram Stain

1. Crystal violet
Gram Stain
2. Grams Iodine (mordant)
Gram Stain

3. Alcohol
Gram Stain

4. Safranin (Counterstain)
 Results
• Gram (+) Purple

• Gram (-) Red

• Difference - due to structure of cell wall

– Gram (+) Thick cell wall
– Gram (-) Thin cell wall
24
 4 groups based on cell wall
composition
1. Gram positive cells
2. Gram negative cells
3. Bacteria without cell walls
4. Bacteria with chemically unique cell walls

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 Bacterial Cell Walls
• Two basic types:
–Gram Positive
–Gram Negative
 The Envelope & Capsule
• The bacterial envelope can be a three
layered structure
–Outer Membrane
–Cell Wall
–Cytoplasmic Membrane
• A capsule may or may not surround
the envelope
28
 The Envelope
• Gram negative bacteria contain all 3
layers
• Have an extra compartment between the
outer membrane (OM) & the cell
membrane (CM) 🡪 periplasmic space
• Gram positive bacteria lack the OM
• Mycoplasma lack OM & CW
Bacterial Envelopes
 Cell Wall
Prokaryotic Cell Walls
– Provides structure and shape
– Protects cell from osmotic forces
– Assists cells in attaching to other cells or
eluding anti-microbial drugs
• Animal Cells 🡪 Do not have cell walls
• Bacterial Cells 🡪 Can target cell wall
with antibiotics
 Bacterial Cell Walls
• Most have cell walls composed of
peptidoglycan. Few lack a cell wall.
• Peptidoglycan 🡪 protein +
polysaccharide, also called Murein
• Peptidoglycan 🡪 form long chains of
alternating sugars, NAG and NAM
• NAG and NAM 🡪 held together by
protein chains
 Peptidoglycan
• unique macromolecule composed of a
repeating framework of long glycan chains
cross-linked by short peptide fragments
• provides strong, flexible support to keep
bacteria from bursting or collapsing because
of changes in osmotic pressure

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Peptidoglycan

34
Peptidoglycan

35
 Bacterial Cell Walls
• Chains of NAG and NAM are
attached to other chains by
tetrapeptide cross bridges
• Tetrapeptide cross bridges 🡪 two
amino acids are L-isomers and two
are D-isomers
• Glycan and peptide linked form a
mesh-like structure
37
 Gram Positive Cell Walls
• Relatively thick layer of peptidoglycan
• Contains unique polysaccharides called
teichoic acid
• Teichoic Acid 🡪 Glycerol or Ribitol
linked to a phosphate group
• Teichoic Acid 🡪 penetrates the
multi-layer cell wall, making it stronger
39
 Gram positive cell wall
• Consists of a thick, homogenous sheath of
peptidoglycan 20-80 nm thick
– tightly bound acidic polysaccharides, including teichoic
acid and lipoteichoic acid (similar in structure with
teichoic acid, though it is attached to lipids in the
plasma membrane)
– Pressed tightly against cell membrane (very little space)
• Retain crystal violet and stain purple

40
 Gram positive cell wall
Functions of teichoic/lipoteichoic acids:

1) cell wall maintenance and enlargement during cell

division;
2) move cations into and out of the cell;
3) stimulate a specific immune response (antigenicity)

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Gram positive wall

42
 Gram Negative Cell Walls

• Have a only a thin layer of

peptidoglycan
• Peptidoglycan mesh is only one
layer thick
Gram- negative cell wall
 Gram negative cell wall
• Consists of
– an outer membrane containing
lipopolysaccharide (LPS)
– thin shell of peptidoglycan
– periplasmic space
– inner membrane
• Lose crystal violet and stain red from
safranin counterstain

46
47
 Outer Membrane
• Only Gram negatives have
an OM
• Composed of a lipid bilayer
– Inner layer 🡪
phospholipids
– Outer layer 🡪
lipopolysacchride (LPS)
• Lipid A
• O-specific side chain
• Core polysaccharide
• LPS also known as
endotoxin
 Lipopolysaccharide
• Lipid A 🡪 hydrophobic
• Polysaccharide 🡪 hydrophilic
• Act as barriers to both polar & nonpolar
substances
 Lipopolysaccharide
• Held to the envelope by lipoprotein
• Bonded to the cell wall on one end, other end
carries lipid that is inserted into the inner
surface
• Most important function is protection
– Makes Gm (-) bacteria more resistant to
antibiotics
– Ex : rifampin equally inhibits RNA pol. But in
Gm (-) can’t reach target
• Only water and a few gases can cross the
lipid part of the OM
• Other molecules pass through pores in the
OM
• Pores formed by proteins 🡪 Porin
Gram positive Gram negative

Fig 4.16
55
 Cytoplasmic Membrane
• Membrane that encloses cytoplasm
• Also called a plasma, cell or unit
membrane
• In prokaryotes & eukaryotes, the
membranes are quite similar
 Unit Membrane
• Phospholipid bilayer
– Hydrophilic head 🡪 sticks out on both sides
– Hydrophobic tail 🡪 2 Fatty Acids, facing each other
• Bilayer studded with proteins 🡪 Carrier or
transporter proteins = ½ the dry weight of the CM
• Proteins can move with in the membrane 🡪 Fluid
Mosiac model
• Bacteria have energy-generating proteins
Fluid Mosaic Model
 External Structures
Appendages: Cell Extensions

-accessory appendages sprouting from

surfaces
Two major groups of appendages:
1. Provide motility (flagella and axial
filaments)
2. Provide attachments (fimbriae and pili)
59
Flagella – bacterial propellers
- for motility or self-propulsion
- allows cell to swim freely
• 3 distinct parts
– filament – long, thin, helical structure composed of
proteins
– hook- curved sheath
– basal body – stack of rings firmly anchored in cell
wall
• rotates 360o
• 1-2 or many distributed over entire cell
• functions in motility
60
Fig 4.2b 61
62
 Flagellar arrangements
1. monotrichous – single flagellum at one end
2. lophotrichous – small bunches arising from
one end of cell
3. amphitrichous – flagella at both ends of cell
4. peritrichous – flagella dispersed over surface
of cell, slowest

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64
 65
Fig 4.5
Chemotaxis

Fig 4.6
66
 axial filaments
• periplasmic, internal flagella, enclosed
between cell wall and cell membrane of
spirochetes
• motility

67
 68
Fig 4.7a b
 fimbriae
• fine hairlike bristles from the cell surface
• function in adhesion to other cells and
surfaces

69
 pili
• rigid tubular structure made of pilin protein
• found only in Gram negative cells

• Functions
– joins bacterial cells for DNA transfer (conjugation)
– adhesion

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Conjugation

71
 glycocalyx
• Coating of molecules external to the cell wall,
made of sugars and/or proteins
• 2 types
1. capsule - highly organized, tightly attached
2. slime layer - loosely organized and attached
• functions
– attachment
– inhibits killing by white blood cells
– receptor

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Fig 4.10
73
2 Types of Glycocalyx

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Biofilms

75
 Cytoplasm
• dense gelatinous solution of sugars, amino
acids, & salts
• 70-80% water
• serves as solvent for materials used in all
cell functions

76
 Chromosome
• single, circular, double-stranded DNA
molecule that contains all the genetic
information required by a cell
• DNA is tightly coiled around a protein,
aggregated in a dense area called the
nucleoid

77
 plasmids
• small circular, double-stranded DNA
• free or integrated into the chromosome
• duplicated and passed on to offspring
• not essential to bacterial growth & metabolism
• may encode antibiotic resistance, tolerance to
toxic metals, enzymes & toxins
• used in genetic engineering- readily manipulated
& transferred from cell to cell

78
 ribosomes
• made of 60% ribosomal RNA & 40%
protein
• consist of 2 subunits: large & small
• procaryotic differ from eucaryotic
ribosomes in size & number of proteins
• site of protein synthesis
• All cells have ribosomes.

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ribosomes

80
 Inclusions, granules
• intracellular storage bodies
• vary in size, number & content
• bacterial cell can use them when
environmental sources are depleted
• Examples: glycogen, poly-β-hydroxybutyrate,
gas vesicles for floating, sulfur and
polyphosphate granules

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Inclusions

82
 endospores
• Resting, dormant cells
• produced by some G+ genera: Clostridium, Bacillus
& Sporosarcina
• Have a 2-phase life cycle – vegetative cell & an
endospore
• sporulation -formation of endospores
• germination- return to vegetative growth
• hardiest of all life forms
• withstand extremes in heat, drying, freezing,
radiation & chemicals not a means of reproduction
83
 endospores
• resistance linked to high levels of calcium &
dipicolinic acid
• dehydrated, metabolically inactive
• thick coat
• longevity verges on immortality 25, 250
million years.
• pressurized steam at 120oC for 20-30
minutes will destroy.
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endospores

85
 Size, Shape and Arrangement of Prokaryotic Cells

Many procaryotes are similar in morphology, but there is a

remarkable amount of variation due to differences in genetics
and ecology.

Shape

1.Coccus – roughly spherical shape; exist as individual cells, but can also
be associated in characteristic arrangements useful in identification
2.Bacilli – rod
3.Vibrios – curved rods
4.Spiral or helices – Spirilla if rigid; Spirochetes if flexible

86
Diplococci (s., diplococcus) - arise when cocci divide and remain
together to form pairs

Neisseria

Long chains of cocci result when cells adhere after repeated divisions in
one plane

Streptococcus, Enterococcus, Lactococcus 87

Staphylococcus divides in random planes to generate irregular grapelike
clumps.

Divisions in two or three planes can produce symmetrical

clusters of cocci.
Micrococcus often divide in two planes to form square groups of four
cells 🡪 tetrads.

Sarcina 🡪 cocci divide in three planes producing cubical 88

packets of eight cells.
Rod- shaped bacteria: ex: Coccobacilli – short and wide,
Bacillus megaterium resembling cocci

rod’s end varies between species:

may be flat, rounded,
cigar-shaped, or bifurcated

Rods occur singly, but they may

Bacillus subtilis remain together after division to
form pairs or chains

Vibrios - curved rod-shaped to

form distinctive commas or
incomplete spirals

89
Vibrios

Coxiella burnetti

90
The oval- to pear-shaped Hyphomicrobium produces a
bud at the end of a long hypha.

Gallionella produce nonliving stalks

A few bacteria actually are flat.

Anthony E. Walsby has discovered square bacteria living
in salt ponds. These bacteria are shaped like flat,
square-to-rectangular boxes about 2 um by 2 to 4 um, and
only 0.25 um thick. Hyphomicrobium

Pleomorphic - variable in shape and lack a single,

characteristic form.
Corynebacterium - generally rodlike form, but no definite
shape.

91
 Gallionella
ferruginea

Rhodospirillum rubrum

Corynebacterium
diphtheriae

Spiroplasma

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93
94
95
Bacteria vary in size as much as in shape

some members of the genus Mycoplasma – smallest - are

about 0.3 um in diameter, approximately the size of the largest
viruses (the poxviruses).

Nanobacteria or ultramicrobacteria – relatively smaller cells; appear

to range from around 0.2 um to less than 0.05 um in diameter. (but still
needs to be studied)

96
Escherichia coli - a bacillus of about average size, is 1.1 to 1.5 um wide
by 2.0 to 6.0 um long.

some spirochetes occasionally reach 500 um in length

cyanobacterium Oscillatoria - about 7 um in diameter (the same diameter

as a red blood cell).

Epulopiscium fishelsoni - a huge bacterium in the intestine of the brown

surgeonfish, Acanthurus nigrofuscus, grows as large as 600 by 80 um

Thiomargarita namibiensis -larger has been discovered in ocean

sediment.

A few bacteria are much larger than the average eucaryotic cell (typical
plant and animal cells are around 10–50 um in diameter).
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Epulopscium fishelsoni

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Thiomargarita namibiensis

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100
101
 Methods in bacterial
identification
1. Microscopic morphology
2. Macroscopic morphology – colony appearance
3. Physiological / biochemical characteristics
4. Chemical analysis
5. Serological analysis
6. Genetic & molecular analysis
• G + C base composition
• DNA analysis using genetic probes
• Nucleic acid sequencing & rRNA analysis

102
 Major Taxonomic Groups of
Bacteria per Bergey’s manual
• Gracilicutes – gram-negative cell walls,
thin-skinned
• Firmicutes – gram-positive cell walls, thick
skinned
• Tenericutes – lack a cell wall & are soft
• Mendosicutes – archaea, primitive
procaryotes with unusual cell walls &
nutritional habits
103
• species –a collection of bacterial cells which share
an overall similar pattern of traits in contrast to
other bacteria whose pattern differs significantly
• strain or variety – a culture derived from a single
parent that differs in structure or metabolism from
other cultures of that species (biovars, morphovars)
• type – a subspecies that can show differences in
antigenic makeup (serotype or serovar),
susceptibility to bacterial viruses (phage type) and
in pathogenicity (pathotype).
104
Procaryotes with unusual
characteristics
 Rickettsias
• very tiny, gram-negative bacteria
• most are pathogens that alternate between mammals
and fleas, lice or ticks
• obligate intracellular pathogens
• cannot survive or multiply outside of a host cell
• cannot carry out metabolism on their own
• Rickettsia rickettisii – Rocky Mountain spotted fever
• Rickettsia prowazekii – epidemic typhus
• Coxiella burnetti – Q fever
106
 Chlamydias
• tiny
• obligate intracellular parasites
• not transmitted by arthropods
• Chlamydia trachomatis – severe eye
infection and one of the most common
sexually transmitted diseases
• Chlamydia psittaci – ornithosis, parrot fever
• Chlamydia pneumoniae – lung infections
107
 Mycoplasmas
• naturally lack a cell wall
• stabilized by sterols, resistant to lysis
• extremely small
• range in shape from filamentous to coccus
or doughnut shaped
• Mycoplasma pneumoniae – atypical
pneumonia in humans
108
 Free-living nonpathogenic
bacteria
• Photosynthetic bacteria
– Cyanobacteria
– Green & purple sulfur bacteria
• Gliding, fruiting bacteria
• Appendaged bacteria
– produce an extended process of the cell wall in
form of a bud, stalk or long thread

109
 Archaea: the other procaryotes
• constitute third Domain Archaea
• seem more closely related to Domain Eukarya than to
bacteria
• contain unique genetic sequences in their rRNA
• have unique membrane lipids & cell wall construction
• live in the most extreme habitats in nature,
extremophiles
• adapted to heat salt acid pH, pressure & atmosphere
• includes: methane producers, hyperthermophiles,
extreme halophiles, and sulfur reducers
110