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CAMPBELL BIOLOGY IN FOCUS
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
24
Early Life and
the Diversification
of Prokaryotes
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
© 2014 Pearson Education, Inc.
Overview: The First Cells
 Earth formed 4.6 billion years ago
 The oldest fossil organisms are prokaryotes dating
back to 3.5 billion years ago
 Prokaryotes are single-celled organisms in the
domains Bacteria and Archaea
 Some of the earliest prokaryotic cells lived in dense
mats that resembled stepping stones
© 2014 Pearson Education, Inc.
Figure 24.1
© 2014 Pearson Education, Inc.
 Prokaryotes are the most abundant organisms
on Earth
 There are more in a handful of fertile soil than the
number of people who have ever lived
 Prokaryotes thrive almost everywhere, including
places too acidic, salty, cold, or hot for most other
organisms
 Some prokaryotes colonize the bodies of other
organisms
© 2014 Pearson Education, Inc.
Figure 24.2
© 2014 Pearson Education, Inc.
Concept 24.1: Conditions on early Earth made
the origin of life possible
 Chemical and physical processes on early Earth may
have produced very simple cells through a sequence
of stages
1. Abiotic synthesis of small organic molecules
2. Joining of these small molecules into macromolecules
3. Packaging of molecules into protocells, membranebound droplets that maintain a consistent internal
chemistry
4. Origin of self-replicating molecules
© 2014 Pearson Education, Inc.
Synthesis of Organic Compounds on Early Earth
 Earth’s early atmosphere likely contained water
vapor and chemicals released by volcanic eruptions
(nitrogen, nitrogen oxides, carbon dioxide, methane,
ammonia, and hydrogen)
 As Earth cooled, water vapor condensed into oceans,
and most of the hydrogen escaped into space
© 2014 Pearson Education, Inc.
 In the 1920s, A. I. Oparin and J. B. S. Haldane
hypothesized that the early atmosphere was a
reducing environment
 In 1953, Stanley Miller and Harold Urey conducted
lab experiments that showed that the abiotic
synthesis of organic molecules in a reducing
atmosphere is possible
© 2014 Pearson Education, Inc.
 However, the evidence is not yet convincing that the
early atmosphere was in fact reducing
 Instead of forming in the atmosphere, the first organic
compounds may have been synthesized near
volcanoes or deep-sea vents
 Miller-Urey-type experiments demonstrate that
organic molecules could have formed with various
possible atmospheres
 Organic molecules have also been found in
meteorites
Video: Hydrothermal Vent
© 2014 Pearson Education, Inc.
Video: Tubeworms
Mass of
amino acids (mg)
Number of
amino acids
Figure 24.3
20
10
0
200
100
0
1953
© 2014 Pearson Education, Inc.
2008
1953
2008
Figure 24.3a
© 2014 Pearson Education, Inc.
Abiotic Synthesis of Macromolecules
 RNA monomers have been produced spontaneously
from simple molecules
 Small organic molecules polymerize when they are
concentrated on hot sand, clay, or rock
© 2014 Pearson Education, Inc.
Protocells
 Replication and metabolism are key properties of life
and may have appeared together
 Protocells may have been fluid-filled vesicles with a
membrane-like structure
 In water, lipids and other organic molecules can
spontaneously form vesicles with a lipid bilayer
© 2014 Pearson Education, Inc.
 Adding clay can increase the rate of vesicle formation
 Vesicles exhibit simple reproduction and metabolism
and maintain an internal chemical environment
© 2014 Pearson Education, Inc.
Relative turbidity, an
index of vesicle number
Figure 24.4
0.4
Precursor molecules plus
montmorillonite clay
0.2
Precursor
molecules only
0
0
40
20
Time (minutes)
60
Vesicle
boundary
1 m
(a) Self-assembly
20 m
(b) Reproduction
© 2014 Pearson Education, Inc.
(c) Absorption of RNA
Relative turbidity, an
index of vesicle number
Figure 24.4a
0.4
Precursor molecules plus
montmorillonite clay
0.2
Precursor
molecules only
0
0
(a) Self-assembly
© 2014 Pearson Education, Inc.
40
20
Time (minutes)
60
Figure 24.4b
20 m
(b) Reproduction
© 2014 Pearson Education, Inc.
Figure 24.4c
Vesicle
boundary
1 m
(c) Absorption of RNA
© 2014 Pearson Education, Inc.
Self-Replicating RNA
 The first genetic material was probably RNA,
not DNA
 RNA molecules called ribozymes have been found
to catalyze many different reactions
 For example, ribozymes can make complementary
copies of short stretches of RNA
© 2014 Pearson Education, Inc.
 Natural selection has produced self-replicating RNA
molecules
 RNA molecules that were more stable or replicated
more quickly would have left the most descendant
RNA molecules
 The early genetic material might have formed an
“RNA world”
© 2014 Pearson Education, Inc.
 Vesicles with RNA capable of replication would
have been protocells
 RNA could have provided the template for DNA, a
more stable genetic material
© 2014 Pearson Education, Inc.
Fossil Evidence of Early Life
 Many of the oldest fossils are stromatolites, layered
rocks that formed from the activities of prokaryotes
up to 3.5 billion years ago
 Ancient fossils of individual prokaryotic cells have
also been discovered
 For example, fossilized prokaryotic cells have been
found in 3.4-billion-year-old rocks from Australia
© 2014 Pearson Education, Inc.
5 cm
30 m
Figure 24.5
10 m
Stromatolites
Nonphotosynthetic bacteria
Possible
earliest
appearance
in fossil record
4
© 2014 Pearson Education, Inc.
Cyanobacteria
3
2
Time (billions of years ago)
1
0
Figure 24.5a
Stromatolites
Nonphotosynthetic bacteria
Possible
earliest
appearance
in fossil record
4
© 2014 Pearson Education, Inc.
Cyanobacteria
1
3
2
Time (billions of years ago)
0
30 m
Figure 24.5b
3-billion-year-old
fossil of a cluster of
nonphotosynthetic
prokaryote cells
© 2014 Pearson Education, Inc.
5 cm
Figure 24.5c
1.1-billion-year-old
fossilized stromatolite
© 2014 Pearson Education, Inc.
Figure 24.5d
10 m
1.5-billion-year-old fossil
of a cyanobacterium
© 2014 Pearson Education, Inc.
 The cyanobacteria that form stromatolites were
the main photosynthetic organisms for over a
billion years
 Early cyanobacteria began the release of oxygen
into Earth’s atmosphere
 Surviving prokaryote lineages either avoided or
adapted to the newly aerobic environment
© 2014 Pearson Education, Inc.
Concept 24.2: Diverse structural and metabolic
adaptations have evolved in prokaryotes
 Most prokaryotes are unicellular, although some
species form colonies
 Most prokaryotic cells have diameters of 0.5–5 µm,
much smaller than the 10–100 µm diameter of many
eukaryotic cells
 Prokaryotic cells have a variety of shapes
 The three most common shapes are spheres (cocci),
rods (bacilli), and spirals
© 2014 Pearson Education, Inc.
1 m
(a) Spherical
(b) Rod-shaped
© 2014 Pearson Education, Inc.
3 m
1 m
Figure 24.6
(c) Spiral
1 m
Figure 24.6a
(a) Spherical
© 2014 Pearson Education, Inc.
1 m
Figure 24.6b
(b) Rod-shaped
© 2014 Pearson Education, Inc.
3 m
Figure 24.6c
(c) Spiral
© 2014 Pearson Education, Inc.
Cell-Surface Structures
 A key feature of nearly all prokaryotic cells is their cell
wall, which maintains cell shape, protects the cell, and
prevents it from bursting in a hypotonic environment
 Eukaryote cell walls are made of cellulose or chitin
 Bacterial cell walls contain peptidoglycan, a network
of modified sugars cross-linked by polypeptides
© 2014 Pearson Education, Inc.
 Archaeal cell walls contain polysaccharides and
proteins but lack peptidoglycan
 Scientists use the Gram stain to classify bacteria by
cell wall composition
 Gram-positive bacteria have simpler walls with a
large amount of peptidoglycan
 Gram-negative bacteria have less peptidoglycan
and an outer membrane that can be toxic
© 2014 Pearson Education, Inc.
Figure 24.7
(a) Gram-positive
bacteria
(b) Gram-negative
bacteria
Carbohydrate portion
of lipopolysaccharide
PeptidoCell glycan
wall layer
Plasma
membrane
Outer
membrane
Cell
wall Peptidoglycan
layer
Plasma membrane
Gram-positive
bacteria
Gram-negative
bacteria
10 m
© 2014 Pearson Education, Inc.
Figure 24.7a
(a) Gram-positive
bacteria
PeptidoCell glycan
wall layer
Plasma
membrane
© 2014 Pearson Education, Inc.
Figure 24.7b
(b) Gram-negative
bacteria
Carbohydrate portion
of lipopolysaccharide
Outer
membrane
Cell
wall Peptidoglycan
layer
Plasma membrane
© 2014 Pearson Education, Inc.
Figure 24.7c
Gram-negative
bacteria
Gram-positive
bacteria
10 m
© 2014 Pearson Education, Inc.
 Many antibiotics target peptidoglycan and damage
bacterial cell walls
 Gram-negative bacteria are more likely to be
antibiotic resistant
 A polysaccharide or protein layer called a capsule
covers many prokaryotes
© 2014 Pearson Education, Inc.
Figure 24.8
Bacterial
cell wall
Bacterial
capsule
Tonsil
cell
200 nm
© 2014 Pearson Education, Inc.
 Some bacteria develop resistant cells called
endospores when they lack an essential nutrient
 Other bacteria have fimbriae, which allow them to
stick to their substrate or other individuals in a
colony
 Pili (or sex pili) are longer than fimbriae and allow
prokaryotes to exchange DNA
© 2014 Pearson Education, Inc.
Figure 24.9
Fimbriae
1 m
© 2014 Pearson Education, Inc.
Motility
 In a heterogeneous environment, many bacteria
exhibit taxis, the ability to move toward or away
from a stimulus
 Chemotaxis is the movement toward or away from
a chemical stimulus
© 2014 Pearson Education, Inc.
 Most motile bacteria propel themselves by flagella
scattered about the surface or concentrated at one
or both ends
 Flagella of bacteria, archaea, and eukaryotes are
composed of different proteins and likely evolved
independently
© 2014 Pearson Education, Inc.
Figure 24.10
Flagellum
Filament
Hook
Motor
Cell wall
Plasma
membrane
© 2014 Pearson Education, Inc.
Rod
Peptidoglycan
layer
20 nm
Figure 24.10a
20 nm
Hook
Motor
© 2014 Pearson Education, Inc.
Evolutionary Origins of Bacterial Flagella
 Bacterial flagella are composed of a motor, hook,
and filament
 Many of the flagella’s proteins are modified versions
of proteins that perform other tasks in bacteria
 Flagella likely evolved as existing proteins were
added to an ancestral secretory system
 This is an example of exaptation, where existing
structures take on new functions through descent
with modification
© 2014 Pearson Education, Inc.
Internal Organization and DNA
 Prokaryotic cells usually lack complex
compartmentalization
 Some prokaryotes do have specialized membranes
that perform metabolic functions
 These are usually infoldings of the plasma membrane
© 2014 Pearson Education, Inc.
Figure 24.11
1 m
0.2 m
Respiratory
membrane
Thylakoid
membranes
(a) Aerobic prokaryote
© 2014 Pearson Education, Inc.
(b) Photosynthetic prokaryote
Figure 24.11a
0.2 m
Respiratory
membrane
(a) Aerobic prokaryote
© 2014 Pearson Education, Inc.
Figure 24.11b
1 m
Thylakoid
membranes
(b) Photosynthetic prokaryote
© 2014 Pearson Education, Inc.
 The prokaryotic genome has less DNA than the
eukaryotic genome
 Most of the genome consists of a circular
chromosome
 The chromosome is not surrounded by a membrane;
it is located in the nucleoid region
 Some species of bacteria also have smaller rings of
DNA called plasmids
© 2014 Pearson Education, Inc.
Figure 24.12
Chromosome
Plasmids
1 m
© 2014 Pearson Education, Inc.
 There are some differences between prokaryotes
and eukaryotes in DNA replication, transcription,
and translation
 These allow people to use some antibiotics to inhibit
bacterial growth without harming themselves
© 2014 Pearson Education, Inc.
Nutritional and Metabolic Adaptations
 Prokaryotes can be categorized by how they obtain
energy and carbon
 Phototrophs obtain energy from light
 Chemotrophs obtain energy from chemicals
 Autotrophs require CO2 as a carbon source
 Heterotrophs require an organic nutrient to make
organic compounds
© 2014 Pearson Education, Inc.
 Energy and carbon sources are combined to give
four major modes of nutrition
 Photoautotrophy
 Chemoautotrophy
 Photoheterotrophy
 Chemoheterotrophy
© 2014 Pearson Education, Inc.
Table 24.1
© 2014 Pearson Education, Inc.
The Role of Oxygen in Metabolism
 Prokaryotic metabolism varies with respect to O2
 Obligate aerobes require O2 for cellular respiration
 Obligate anaerobes are poisoned by O2 and use
fermentation or anaerobic respiration, in which
substances other than O2 act as electron acceptors
 Facultative anaerobes can survive with or without O2
© 2014 Pearson Education, Inc.
Nitrogen Metabolism
 Nitrogen is essential for the production of amino
acids and nucleic acids
 Prokaryotes can metabolize nitrogen in a variety of
ways
 In nitrogen fixation, some prokaryotes convert
atmospheric nitrogen (N2) to ammonia (NH3)
© 2014 Pearson Education, Inc.
Metabolic Cooperation
 Cooperation between prokaryotes allows them to use
environmental resources they could not use as
individual cells
 In the cyanobacterium Anabaena, photosynthetic
cells and nitrogen-fixing cells called heterocysts (or
heterocytes) exchange metabolic products
© 2014 Pearson Education, Inc.
Figure 24.13
Photosynthetic
cells
Heterocyst
20 m
© 2014 Pearson Education, Inc.
 In some prokaryotic species, metabolic cooperation
occurs in surface-coating colonies called biofilms
© 2014 Pearson Education, Inc.
Reproduction
 Prokaryotes reproduce quickly by binary fission and
can divide every 1–3 hours
 Key features of prokaryotic biology allow them to
divide quickly
 They are small
 They reproduce by binary fission
 They have short generation times
© 2014 Pearson Education, Inc.
Adaptations of Prokaryotes: A Summary
 The ongoing success of prokaryotes is an
extraordinary example of physiological and
metabolic diversification
 Prokaryotic diversification can be viewed as a first
great wave of adaptive radiation in the evolutionary
history of life
© 2014 Pearson Education, Inc.
Concept 24.3: Rapid reproduction, mutation, and
genetic recombination promote genetic diversity
in prokaryotes
 Prokaryotes have considerable genetic variation
 Three factors contribute to this genetic diversity
 Rapid reproduction
 Mutation
 Genetic recombination
© 2014 Pearson Education, Inc.
Rapid Reproduction and Mutation
 Prokaryotes reproduce by binary fission, and
offspring cells are generally identical
 Mutation rates during binary fission are low, but
because of rapid reproduction, mutations can
accumulate rapidly in a population
 High diversity from mutations allows for rapid
evolution
 Prokaryotes are not “primitive” but are highly
evolved
© 2014 Pearson Education, Inc.
Figure 24.14
Experiment
Daily serial transfer
0.1 mL
(population sample)
Old tube
(discarded
after
transfer)
New tube
(9.9 mL
growth
medium)
Population growth rate
(relative to ancestral
population)
Results
1.8
1.6
1.4
1.2
1.0
0
© 2014 Pearson Education, Inc.
5,000
10,000 15,000
Generation
20,000
Figure 24.14a
Population growth rate
(relative to ancestral
population)
Results
1.8
1.6
1.4
1.2
1.0
0
© 2014 Pearson Education, Inc.
5,000
10,000 15,000
Generation
20,000
Genetic Recombination
 Genetic recombination, the combining of DNA from
two sources, contributes to diversity
 Prokaryotic DNA from different individuals can be
brought together by transformation, transduction,
and conjugation
 Movement of genes among individuals from
different species is called horizontal gene transfer
© 2014 Pearson Education, Inc.
Transformation and Transduction
 A prokaryotic cell can take up and incorporate
foreign DNA from the surrounding environment in a
process called transformation
 Transduction is the movement of genes between
bacteria by bacteriophages (viruses that infect
bacteria)
© 2014 Pearson Education, Inc.
Figure 24.15-1
1 Phage infects bacterial
donor cell with A and
B alleles.
Phage DNA
A B
Donor cell
© 2014 Pearson Education, Inc.
Figure 24.15-2
1 Phage infects bacterial
donor cell with A and
B alleles.
Phage DNA
A B
Donor cell
2 Phage DNA is
replicated and
proteins synthesized.
© 2014 Pearson Education, Inc.
A
B
Figure 24.15-3
1 Phage infects bacterial
donor cell with A and
B alleles.
Phage DNA
A B
Donor cell
2 Phage DNA is
replicated and
proteins synthesized.
A
B
3 Fragment of DNA with
A allele is packaged
within a phage capsid.
© 2014 Pearson Education, Inc.
A
Figure 24.15-4
Phage DNA
1 Phage infects bacterial
donor cell with A and
B alleles.
A B
Donor cell
2 Phage DNA is
A
replicated and
proteins synthesized.
B
3 Fragment of DNA with
A allele is packaged
within a phage capsid.
4 Phage with
A
allele
infects bacterial
recipient cell.
A
Crossing over
A
A−
B−
Recipient
cell
© 2014 Pearson Education, Inc.
Figure 24.15-5
Phage DNA
1 Phage infects bacterial
donor cell with A and
B alleles.
A B
Donor cell
2 Phage DNA is
A
replicated and
proteins synthesized.
B
3 Fragment of DNA with
A allele is packaged
within a phage capsid.
4 Phage with
A
A
Crossing over
allele
infects bacterial
recipient cell.
5 Incorporation of phage
DNA creates recombinant
cell with genotype AB.
© 2014 Pearson Education, Inc.
A
A−
B−
Recipient
cell
Recombinant
cell
A B−
Conjugation and Plasmids
 Conjugation is the process where genetic material
is transferred between prokaryotic cells
 In bacteria, the DNA transfer is one way
 In E. coli, the donor cell attaches to a recipient by a
pilus, pulls it closer, and transfers DNA
© 2014 Pearson Education, Inc.
Figure 24.16
1 m
Sex pilus
© 2014 Pearson Education, Inc.
 The F factor is a piece of DNA required for the
production of pili
 Cells containing the F plasmid (F+) function as DNA
donors during conjugation
 Cells without the F factor (F–) function as DNA
recipients during conjugation
 The F factor is transferable during conjugation
© 2014 Pearson Education, Inc.
Figure 24.17-1
F plasmid
F cell
(donor)
Bacterial
chromosome
Mating
bridge
F− cell
(recipient)
Bacterial
chromosome
1 One strand of
F cell plasmid
DNA breaks at
arrowhead.
© 2014 Pearson Education, Inc.
Figure 24.17-2
F plasmid
F cell
(donor)
Bacterial
chromosome
Mating
bridge
F− cell
(recipient)
Bacterial
chromosome
1 One strand of
F cell plasmid
DNA breaks at
arrowhead.
© 2014 Pearson Education, Inc.
2 Broken strand
peels off and
enters F− cell.
Figure 24.17-3
F plasmid
F cell
(donor)
Bacterial
chromosome
Mating
bridge
F− cell
(recipient)
Bacterial
chromosome
1 One strand of
F cell plasmid
DNA breaks at
arrowhead.
© 2014 Pearson Education, Inc.
2 Broken strand
peels off and
enters F− cell.
3 Donor and
recipient cells
synthesize
complementary
DNA strands.
Figure 24.17-4
F plasmid
F cell
(donor)
Bacterial
chromosome
F
cell
Mating
bridge
F− cell
(recipient)
F
cell
Bacterial
chromosome
1 One strand of
F cell plasmid
DNA breaks at
arrowhead.
© 2014 Pearson Education, Inc.
2 Broken strand
peels off and
enters F− cell.
3 Donor and
recipient cells
synthesize
complementary
DNA strands.
4 Recipient cell
is now a
recombinant
F cell.
 The F factor can also be integrated into the
chromosome
 A cell with the F factor built into its chromosomes
functions as a donor during conjugation
 The recipient becomes a recombinant bacterium,
with DNA from two different cells
© 2014 Pearson Education, Inc.
R Plasmids and Antibiotic Resistance
 Genes for antibiotic resistance are carried in R
plasmids
 Antibiotics kill sensitive bacteria, but not bacteria with
specific R plasmids
 Through natural selection, the fraction of bacteria
with genes for resistance increases in a population
exposed to antibiotics
 Antibiotic-resistant strains of bacteria are becoming
more common
© 2014 Pearson Education, Inc.
Concept 24.4: Prokaryotes have radiated into a
diverse set of lineages
 Prokaryotes have radiated extensively due to
diverse structural and metabolic adaptations
 Prokaryotes inhabit every environment known to
support life
© 2014 Pearson Education, Inc.
An Overview of Prokaryotic Diversity
 Applying molecular systematics to the investigation
of prokaryotic phylogeny has produced dramatic
results
 Molecular systematics led to the splitting of
prokaryotes into bacteria and archaea
 Molecular systematists continue to work on the
phylogeny of prokaryotes
© 2014 Pearson Education, Inc.
Figure 24.18
Euryarchaeotes
Crenarchaeotes
UNIVERSAL
ANCESTOR
Nanoarchaeotes
Domain Archaea
Korarchaeotes
Domain
Eukarya
Eukaryotes
Proteobacteria
Spirochetes
Cyanobacteria
Gram-positive
bacteria
© 2014 Pearson Education, Inc.
Domain Bacteria
Chlamydias
 The use of polymerase chain reaction (PCR) has
allowed for more rapid sequencing of prokaryote
genomes
 A handful of soil may contain 10,000 prokaryotic
species
 Horizontal gene transfer between prokaryotes
obscures the root of the tree of life
© 2014 Pearson Education, Inc.
Bacteria
 Bacteria include the vast majority of prokaryotes
familiar to most people
 Diverse nutritional types are scattered among the
major groups of bacteria
Video: Tubeworms
© 2014 Pearson Education, Inc.
Figure 24.UN01
Eukarya
Archaea
Bacteria
© 2014 Pearson Education, Inc.
Figure 24.19a
Beta subgroup
Alpha subgroup
© 2014 Pearson Education, Inc.
1 m
Nitrosomonas
(TEM)
Delta subgroup
Epsilon subgroup
Chondromyces
crocatus (SEM)
2 m
Rhizobium (arrows)
(TEM)
300 m
Thiomargarita
namibiensis (LM)
200 m
Gamma subgroup
2.5 m
Alpha
Beta
Gamma Proteobacteria
Delta
Epsilon
Helicobacter pylori
(TEM)
 Proteobacteria are gram-negative bacteria including
photoautotrophs, chemoautotrophs, and
heterotrophs
 Some are anaerobic and others aerobic
© 2014 Pearson Education, Inc.
Figure 24.19aa
Alpha
Beta
Gamma Proteobacteria
Delta
Epsilon
© 2014 Pearson Education, Inc.
 Members of the subgroup alpha proteobacteria
are closely associated with eukaryotic hosts in
many cases
 Scientists hypothesize that mitochondria evolved
from aerobic alpha proteobacteria through
endosymbiosis
 Example: Rhizobium, which forms root nodules in
legumes and fixes atmospheric N2
 Example: Agrobacterium, which produces tumors in
plants and is used in genetic engineering
© 2014 Pearson Education, Inc.
Figure 24.19ab
Alpha subgroup
2.5 m
Rhizobium (arrows)
inside a root cell of
a legume (TEM)
© 2014 Pearson Education, Inc.
 Members of the subgroup beta proteobacteria are
nutritionally diverse
 Example: the soil bacterium Nitrosomonas, which
converts NH4+ to NO2–
© 2014 Pearson Education, Inc.
Figure 24.19ac
Beta subgroup
1 m
Nitrosomonas
(colorized TEM)
© 2014 Pearson Education, Inc.
 The subgroup gamma proteobacteria includes
sulfur bacteria such as Thiomargarita namibiensis
and pathogens such as Legionella, Salmonella, and
Vibrio cholerae
 Escherichia coli resides in the intestines of many
mammals and is not normally pathogenic
© 2014 Pearson Education, Inc.
Figure 24.19ad
Gamma subgroup
200 m
Thiomargarita
namibiensis containing
sulfur wastes (LM)
© 2014 Pearson Education, Inc.
 The subgroup delta proteobacteria includes the
slime-secreting myxobacteria and bdellovibrios, a
bacteria that attacks other bacteria
© 2014 Pearson Education, Inc.
Figure 24.19ae
Delta subgroup
300 m
Fruiting bodies of
Chondromyces crocatus,
a myxobacterium (SEM)
© 2014 Pearson Education, Inc.
 The subgroup epsilon proteobacteria contains
many pathogens including Campylobacter, which
causes blood poisoning, and Helicobacter pylori,
which causes stomach ulcers
© 2014 Pearson Education, Inc.
Figure 24.19af
Epsilon subgroup
2 m
Helicobacter pylori
(colorized TEM)
© 2014 Pearson Education, Inc.
Figure 24.19b
Cyanobacteria
Chlamydia (arrows)
(TEM)
5 m
2.5 m
Spirochetes
Oscillatoria
Leptospira
(TEM)
5 m
2 m
Gram-positive bacteria
Streptomyces
(SEM)
© 2014 Pearson Education, Inc.
40 m
Chlamydias
Mycoplasmas
(SEM)
 Chlamydias are parasites that live within
animal cells
 Chlamydia trachomatis causes blindness and
nongonococcal urethritis by sexual transmission
© 2014 Pearson Education, Inc.
Figure 24.19ba
Chlamydias
2.5 m
Chlamydia (arrows)
inside an animal cell
(colorized TEM)
© 2014 Pearson Education, Inc.
 Spirochetes are helical heterotrophs
 Some are parasites, including Treponema pallidum,
which causes syphilis, and Borrelia burgdorferi,
which causes Lyme disease
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Figure 24.19bb
Spirochetes
5 m
Leptospira,
a spirochete
(colorized TEM)
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 Cyanobacteria are photoautotrophs that generate O2
 Plant chloroplasts likely evolved from cyanobacteria
by the process of endosymbiosis
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Figure 24.19bc
Cyanobacteria
40 m
Oscillatoria,
a filamentous
cyanobacterium
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 Gram-positive bacteria include
 Actinomycetes, which decompose soil
 Streptomyces, which are a source of antibiotics
 Bacillus anthracis, the cause of anthrax
 Clostridium botulinum, the cause of botulism
 Some Staphylococcus and Streptococcus, which can
be pathogenic
 Mycoplasms, the smallest known cells
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Figure 24.19bd
Gram-positive bacteria
5 m
Streptomyces,
the source of
many antibiotics
(SEM)
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Figure 24.19be
Gram-positive bacteria
2 m
Hundreds of mycoplasmas
covering a human
fibroblast cell
(colorized SEM)
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Archaea
 Archaea share certain traits with bacteria and other
traits with eukaryotes
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Figure 24.UN02
Eukarya
Archaea
Bacteria
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Table 24.2
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Table 24.2a
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Table 24.2b
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 Some archaea live in extreme environments and are
called extremophiles
 Extreme halophiles live in highly saline
environments
 Extreme thermophiles thrive in very hot
environments
Video: Cyanobacteria (Oscillatoria)
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Figure 24.20
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 Methanogens produce methane as a waste product
 Methanogens are strict anaerobes and are poisoned
by O2
 Methanogens live in swamps and marshes, in the
guts of cattle, and near deep-sea hydrothermal
vents
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Figure 24.21
2 m
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Figure 24.21a
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Figure 24.21b
2 m
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 Recent metagenomic studies have revealed many
new groups of archaea
 Some of these may offer clues to the early evolution
of life on Earth
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Concept 24.5: Prokaryotes play crucial roles in
the biosphere
 Prokaryotes are so important that if they were to
disappear, the prospects for any other life surviving
would be dim
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Chemical Recycling
 Prokaryotes play a major role in the recycling of
chemical elements between the living and nonliving
components of ecosystems
 Chemoheterotrophic prokaryotes function as
decomposers, breaking down dead organisms
and waste products
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 Prokaryotes can sometimes increase the availability
of nitrogen, phosphorus, and potassium for plant
growth
 Prokaryotes can also “immobilize” or decrease the
availability of nutrients
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Uptake of K by plants (mg)
Figure 24.22
1.0
0.8
0.6
0.4
0.2
Seedlings growing in the lab
0
No
Strain 1 Strain 2 Strain 3
bacteria
Soil treatment
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Figure 24.22a
Seedlings growing in the lab
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Ecological Interactions
 Symbiosis is an ecological relationship in which
two species live in close contact: a larger host and
smaller symbiont
 Prokaryotes often form symbiotic relationships with
larger organisms
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 In mutualism, both symbiotic organisms benefit
 In commensalism, one organism benefits while
neither harming nor helping the other in any
significant way
 In parasitism, an organism called a parasite harms
but does not kill its host
 Parasites that cause disease are called pathogens
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Figure 24.23
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 The ecological communities of hydrothermal vents
depend on chemoautotrophic bacteria for energy
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Impact on Humans
 The best-known prokaryotes are pathogens, but
many others have positive interactions with humans
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Mutualistic Bacteria
 Human intestines are home to about 500–1,000
species of bacteria
 Many of these are mutualists and break down food
that is undigested by our intestines
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Pathogenic Bacteria
 Prokaryotes cause about half of all human diseases
 For example, Lyme disease is caused by a bacterium
and carried by ticks
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Figure 24.24
5 m
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Figure 24.24a
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Figure 24.24b
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Figure 24.24c
5 m
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 Pathogenic prokaryotes typically cause disease by
releasing exotoxins or endotoxins
 Exotoxins are secreted and cause disease even if
the prokaryotes that produce them are not present
 Endotoxins are released only when bacteria die
and their cell walls break down
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 Horizontal gene transfer can spread genes
associated with virulence
 For example, pathogenic strains of the normally
harmless E. coli bacteria have emerged through
horizontal gene transfer
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Prokaryotes in Research and Technology
 Experiments using prokaryotes have led to important
advances in DNA technology
 For example, E. coli is used in gene cloning
 For example, Agrobacterium tumefaciens is used to
produce transgenic plants
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 Bacteria can now be used to make natural plastics
 Prokaryotes are the principal agents in
bioremediation, the use of organisms to remove
pollutants from the environment
 Bacteria can be engineered to produce vitamins,
antibiotics, and hormones
 Bacteria are also being engineered to produce
ethanol from waste biomass
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Figure 24.25
(b)
(a)
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Figure 24.25a
(a)
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Figure 24.25b
(b)
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Figure 24.26
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Figure 24.UN03
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Figure 24.UN04
Fimbriae
Cell wall
Circular
chromosome
Capsule
Sex pilus
Internal
organization
Flagella
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Figure 24.UN05
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