Lecture PowerPoint to accompany
Foundations in
Microbiology
Seventh Edition
Talaro
Chapter 4
An Introduction to the
Prokaryotic Cell, Its
Organization, and Members
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
4.1 Characteristics of Cells and Life
All living things (single and multicellular) are
made of cells that share some common
characteristics:
– Basic shape – spherical, cubical, cylindrical
– Internal content – cytoplasm, surrounded by a
membrane
– DNA chromosome(s), ribosomes, metabolic
capabilities
Two basic cell types: eukaryotic and prokaryotic
2
Characteristics of Cells
Eukaryotic cells: animals, plants, fungi, and
protists
– Contain membrane-bound organelles that
compartmentalize the cytoplasm and perform specific
functions
– Contain double-membrane bound nucleus with DNA
chromosomes
Prokaryotic cells: bacteria and archaea
– No nucleus or other membrane-bound organelles
3
Characteristics of Life
• Reproduction and heredity – genome composed of
DNA packed in chromosomes; produce offspring
sexually or asexually
• Growth and development
• Metabolism – chemical and physical life processes
• Movement and/or irritability – respond to
internal/external stimuli; self-propulsion of many
organisms
• Cell support, protection, and storage mechanisms – cell
walls, vacuoles, granules and inclusions
• Transport of nutrients and waste
4
4.3 Prokaryotic Profiles
5
Prokaryotic Profiles
• Structures that are essential to the functions
of all prokaryotic cells are a cell membrane,
cytoplasm, ribosomes, and one (or a few)
chromosomes
6
Figure 4.1 Structure of a bacterial cell
7
4.3 External Structures
• Appendages
– Two major groups of appendages:
• Motility – flagella and axial filaments (periplasmic
flagella)
• Attachment or channels – fimbriae and pili
• Glycocalyx – surface coating
8
Flagella
• 3 parts:
– Filament – long, thin, helical structure composed of protein
Flagellin
– Hook – curved sheath
– Basal body – stack of rings firmly anchored in cell wall
• Rotates 360o
• Number and arrangement of flagella varies:
– Monotrichous, lophotrichous, amphitrichous, peritrichous
• Functions in motility of cell through environment
9
Figure 4.2 Flagella
10
Flagellar Arrangements
1. Monotrichous – single flagellum at one end
2. Lophotrichous – small bunches emerging
from the same site
3. Amphitrichous – flagella at both ends of cell
4. Peritrichous – flagella dispersed over surface
of cell; slowest
11
Figure 4.3 Electron micrographs of
flagellar arrangements
12
Flagellar Responses
Guide bacteria in a direction in response to external
stimulus:
Chemical stimuli – chemotaxis; positive and negative
Light stimuli – phototaxis
Signal sets flagella into rotary motion clockwise or
counterclockwise:
Counterclockwise – results in smooth linear direction –
run
Clockwise – tumbles
13
Figure 4.4 The operation of flagella
14
Figure 4.5 Chemotaxis in bacteria
15
Periplasmic Flagella
• Internal flagella, enclosed in the space
between the outer sheath and the cell wall
peptidoglycan
• Produce cellular motility by contracting and
imparting twisting or flexing motion
16
Figure 4.6 Periplasmic flagella
17
Fimbriae
• Fine, proteinaceous, hairlike bristles
emerging from the cell surface
• Function in adhesion to other cells and
surfaces
18
Pili
• Rigid tubular structure made of pilin protein
• Found only in gram-negative cells
• Function to join bacterial cells for partial DNA
transfer called conjugation
19
Glycocalyx
•
Coating of molecules external to the cell wall,
made of sugars and/or proteins
Two types:
•
1. Slime layer - loosely organized and attached
2. Capsule - highly organized, tightly attached
•
Functions:
–
–
–
Protect cells from dehydration and nutrient loss
Inhibit killing by white blood cells by phagocytosis,
contributing to pathogenicity
Attachment - formation of biofilms
20
21
22
Figure 4.11 Biofilm on a catheter
23
4.4 The Cell Envelope
• External covering outside the cytoplasm
• Composed of two basic layers:
– Cell wall and cell membrane
• Maintains cell integrity
• Two different groups of bacteria demonstrated
by Gram stain:
– Gram-positive bacteria: thick cell wall composed
primarily of peptidoglycan and cell membrane
– Gram-negative bacteria: outer cell membrane,
thin peptidoglycan layer, and cell membrane
24
Figure 4.12
Insert figure 4.12
Comparative cell envelopes
25
Structure of Cell Walls
• Determines cell shape, prevents lysis
(bursting) or collapsing due to changing
osmotic pressures
• Peptidoglycan is primary component:
– Unique macromolecule composed of a
repeating framework of long glycan chains
cross-linked by short peptide fragments
26
Figure 4.13 Peptidoglycan
27
Gram-Positive Cell Wall
• Thick, homogeneous sheath of peptidoglycan
– 20-80 nm thick
– Includes teichoic acid and lipoteichoic acid:
function in cell wall maintenance and enlargement
during cell division; move cations across the cell
envelope; stimulate a specific immune response
– Some cells have a periplasmic space, between the
cell membrane and cell wall
28
Figure 4.12
29
Gram-Negative Cell Wall
• Composed of an outer membrane and a thin
peptidoglycan layer
• Outer membrane is similar to cell membrane bilayer
structure
– Outermost layer contains lipopolysaccharides and
lipoproteins (LPS)
• Lipid portion (endotoxin) may become toxic when released
during infections
• May function as receptors and blocking immune response
• Contain porin proteins in upper layer – regulate molecules
entering and leaving cell
– Bottom layer is a thin sheet of peptidoglycan
• Periplasmic space above and below peptidoglycan
30
31
Table 4.1 Comparison of Gram-Positive and Gram-Negative
32
The Gram Stain
• Differential stain that distinguishes cells with a grampositive cell wall from those with a gram-negative cell
wall
– Gram-positive - retain crystal violet and stain purple
– Gram-negative - lose crystal violet and stain red from
safranin counterstain
• Important basis of bacterial classification and
identification
• Practical aid in diagnosing infection and guiding drug
treatment
33
34
Nontypical Cell Walls
• Some bacterial groups lack typical cell wall
structure, i.e., Mycobacterium and Nocardia
– Gram-positive cell wall structure with lipid
mycolic acid (cord factor)
• Pathogenicity and high degree of resistance to certain
chemicals and dyes
• Basis for acid-fast stain used for diagnosis of infections
caused by these microorganisms
• Some have no cell wall, i.e., Mycoplasma
– Cell wall is stabilized by sterols
– Pleomorphic
35
Figure 4.15 Extreme variation in shape of
Mycoplasma pneumoniae
36
Cell Membrane Structure
• Phospholipid bilayer with embedded proteins –
fluid mosaic model
• Functions in:
– Providing site for energy reactions, nutrient processing, and
synthesis
– Passage of nutrients into the cell and the discharge of wastes
• Cell membrane is selectively permeable
37
Figure 4.16 Cell membrane structure
38
4.5 Bacterial Internal Structures
• Cell cytoplasm:
– Dense gelatinous solution of sugars, amino acids,
and salts
– 70-80% water
• Serves as solvent for materials used in all cell functions
39
Bacterial Internal Structures
• Chromosome
– Single, circular, double-stranded DNA
molecule that contains all the genetic
information required by a cell
– Aggregated in a dense area called the nucleoid
• DNA is tightly coiled
40
Figure 4.17 Chromosome structure
41
Bacterial Internal Structures
• Plasmids
–
–
–
–
–
Small circular, double-stranded DNA
Free or integrated into the chromosome
Duplicated and passed on to offspring
Not essential to bacterial growth and metabolism
May encode antibiotic resistance, tolerance to toxic
metals, enzymes, and toxins
– Used in genetic engineering - readily manipulated
and transferred from cell to cell
42
Bacterial Internal Structures
• Ribosomes
– Made of 60% ribosomal RNA and 40% protein
– Consist of two subunits: large and small
– Prokaryotic differ from eukaryotic ribosomes in
size and number of proteins
– Site of protein synthesis
– Present in all cells
43
Figure 4.18 Prokaryotic ribosome
44
Bacterial Internal Structures
• Inclusions and granules
– Intracellular storage bodies
– Vary in size, number, and content
– Bacterial cell can use them when environmental
sources are depleted
– Examples: glycogen, poly b-hydroxybutyrate, gas
vesicles for floating, sulfur and phosphate
granules (metachromatic granules), particles of
iron oxide
45
Figure 4.19 Bacterial inclusion bodies
46
Bacterial Internal Structures
• Cytoskeleton
– Many bacteria possess an internal network of
protein polymers that is closely associated with
the cell wall
47
Bacterial Internal Structures
• Endospores
– Inert, resting, cells produced by some G+ genera:
Clostridium, Bacillus, and Sporosarcina
• Have a 2-phase life cycle:
– Vegetative cell – metabolically active and growing
– Endospore – when exposed to adverse environmental conditions;
capable of high resistance and very long-term survival
– Sporulation - formation of endospores
• Hardiest of all life forms
• Withstands extremes in heat, drying, freezing, radiation, and
chemicals
• Not a means of reproduction
– Germination - return to vegetative growth
48
Figure 4.22 Sporulation cycle
49
Endospores
• Resistance linked to high levels of calcium and
dipicolinic acid
• Dehydrated, metabolically inactive
• Thick coat
• Longevity verges on immortality, 250 million
years
• Resistant to ordinary cleaning methods and boiling
• Pressurized steam at 120oC for 20-30 minutes will
destroy
50
4.6 Bacterial Shapes,
Arrangements, and Sizes
• Vary in shape, size, and arrangement but
typically described by one of three basic
shapes:
– Coccus – spherical
– Bacillus – rod
• Coccobacillus – very short and plump
• Vibrio – gently curved
– Spirillum – helical, comma, twisted rod,
• Spirochete – spring-like
51
Figure 4.23 Common bacterial shapes
52
Table 4.2 Comparison of Spiral-Shaped Bacteria
53
Bacterial Shapes, Arrangements, and
Sizes
• Arrangement of cells is dependent on pattern of
division and how cells remain attached after division:
– Cocci:
•
•
•
•
•
•
Singles
Diplococci – in pairs
Tetrads – groups of four
Irregular clusters
Chains
Cubical packets (sarcina)
– Bacilli:
• Diplobacilli
• Chains
• Palisades
54
Figure 4.25 Arrangement of cocci
55
Figure 4.26 The dimensions of bacteria
56
4.7 Classification Systems
in the Prokaryotae
1.
2.
3.
4.
5.
Microscopic morphology
Macroscopic morphology – colony appearance
Bacterial physiology
Serological analysis
Genetic and molecular analysis
57
Bacterial Taxonomy Based on
Bergey’s Manual
• Bergey’s Manual of Determinative Bacteriology –
five volume resource covering all known
prokaryotes
– Classification based on genetic information –
phylogenetic
– Two domains: Archaea and Bacteria
– Five major subgroups with 25 different phyla
58
Major Taxonomic Groups of Bacteria
• Domain Archaea – primitive, adapted to
extreme habitats and modes of nutrition
• Domain Bacteria:
– Phylum Proteobacteria – Gram-negative cell
walls
– Phylum Firmicutes – mainly gram-positive
with low G + C content
– Phylum Actinobacteria – Gram-positive with
high G + C content
59
Figure 4.27 Universal phylogenetic tree
60
Table 4.3 General Classification Scheme
61
Diagnostic Scheme for Medical Use
• Uses phenotypic qualities in identification
– Restricted to bacterial disease agents
– Divides bacteria based on cell wall structure,
shape, arrangement, and physiological traits
62
63
Species and Subspecies
• 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)
64
Prokaryotes with Unusual Characteristics
• Free-living nonpathogenic bacteria
• Photosynthetic bacteria – use photosynthesis, can
synthesize required nutrients from inorganic
compounds
– Cyanobacteria (blue-green algae)
• Gram-negative cell walls
• Extensive thylakoids with photosynthetic chlorophyll pigments
and gas inclusions
– Green and purple sulfur bacteria
• Contain photosynthetic pigment bacteriochlorophyll
• Do not give off oxygen as a product of photosynthesis
– Gliding, fruiting bacteria
• Gram-negative
• Glide over moist surfaces
65
Figure 4.28 Structure of cyanobacteria
66
Figure 4.29 Photosynthetic bacteria
67
Unusual Forms of
Medically Significant Bacteria
• Obligate intracellular parasites
– Rickettsias
• Very tiny, gram-negative bacteria
• Most are pathogens that alternate between mammals and
blood-sucking arthropods
• 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 typhi – endemic typhus
68
Unusual Forms of
Medically Significant Bacteria
– Chlamydias
•
•
•
•
Tiny
Obligate intracellular parasites
Not transmitted by arthropods
Chlamydia trachomatis – severe eye infection and
one of the most common sexually transmitted
diseases
• Chlamydia pneumoniae – lung infections
69
4.8 Archaea: The Other Prokaryotes
• 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 and cell wall construction
• Live in the most extreme habitats in nature,
extremophiles
• Adapted to heat, salt, acid pH, pressure, and atmosphere
• Includes: methane producers, hyperthermophiles,
extreme halophiles, and sulfur reducers
70
Archaea
71
Table 4.5 Comparison of Three Cellular Domains
72