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CAMPBELL BIOLOGY IN FOCUS
URRY • CAIN • WASSERMAN • MINORSKY • REECE
24
Early Life and the
Diversification
of Prokaryotes
Mr. Karns
SECOND EDITION
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; others were free-floating individual cells
© 2016 Pearson
Figure 24.1
© 2016 Pearson Education, Inc.
 Prokaryotes are the most abundant organisms
on Earth
 They thrive in most environments, including places
too acidic, salty, cold, or hot for most other
organisms
 Some prokaryotes colonize the bodies of other
organisms
© 2016 Pearson Education, Inc.
Figure 24.2
© 2016 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
© 2016 Pearson
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
© 2016 Pearson
 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
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 Some evidence suggests that the early atmosphere
was neither reducing nor oxidizing
 The first organic compounds may have been
synthesized in areas with reducing conditions such
as volcanoes or deep-sea vents
 Amino acids can form spontaneously in conditions
simulating volcanic eruptions
© 2016 Pearson Education, Inc.
© 2016 Pearson Education, Inc.
20
10
0
1953
2008
Mass of amino acids (mg)
Number of amino acids
Figure 24.3
200
100
0
1953
2008
Figure 24.3-1
© 2016 Pearson Education, Inc.
 The first organic molecules may have been brought
to Earth in meteorites
 For example, the Murchison meteorite contained
several key organic molecules
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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
 Amino acid polymers may have functioned as weak
catalysts for chemical reactions on early Earth
© 2016 Pearson
Protocells
 Replication and metabolism are key properties of
life and may have appeared together in early
protocells
 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
© 2016 Pearson
 Adding clay can increase the rate of vesicle
formation
 Vesicles exhibit simple reproduction and
metabolism and maintain an internal chemical
environment
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Relative turbidity, an
Index of vesicle number
Figure 24.4
0.4
Precursor molecules plus
montmorillonite clay
Precursor
molecules only
0.2
0
0
20
40
Time (minutes)
60
(a) Self-assembly
Vesicle
boundary
1 mm
20 mm
(b) Reproduction
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(c) Absorption of RNA
Relative turbidity, an
Index of vesicle number
Figure 24.4-1
0.4
Precursor molecules plus
montmorillonite clay
Precursor
molecules only
0.2
0
0
(a) Self-assembly
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20
40
Time (minutes)
60
Figure 24.4-2
20 mm
(b) Reproduction
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Figure 24.4-3
Vesicle
boundary
1 mm
(c) Absorption of RNA
© 2016 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
© 2016 Pearson
 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”
© 2016 Pearson Education, Inc.
 Vesicles with self-replicating, catalytic RNA would
have been able to produce daughter protocells with
properties similar to those of their parent
 RNA may have provided the template for DNA, a
more stable genetic material
© 2016 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
© 2016 Pearson
5 cm
30 mm
Figure 24.5
10 mm
Stromatolites
Nonphotosynthetic bacteria
Possible
earliest
appearance
in fossil record
4
© 2016 Pearson Education, Inc.
Cyanobacteria
3
1
2
Time (billions of years ago)
0
Figure 24.5-1
Stromatolites
Nonphotosynthetic bacteria
Possible
earliest
appearance
in fossil record
4
© 2016 Pearson Education, Inc.
Cyanobacteria
3
2
1
Time (billions of years ago)
0
30 mm
Figure 24.5-2
3-billion-year-old
fossil of a
cluster of
nonphotosynthetic
prokaryotes
© 2016 Pearson Education, Inc.
5 cm
Figure 24.5-3
1.1-billion-year-old
fossilized
stromatolite
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Figure 24.5-4
10 mm
1.5-billion-year-old fossil
of a cyanobacterium
© 2016 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
© 2016 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
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(a) Spherical
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(b) Rod-shaped
3 mm
1 mm
1 mm
Figure 24.6
(c) Spiral
1 mm
Figure 24.6-1
(a) Spherical
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1 mm
Figure 24.6-2
(b) Rod-shaped
© 2016 Pearson Education, Inc.
3 mm
Figure 24.6-3
(c) Spiral
© 2016 Pearson Education, Inc.
Cell-Surface Structures
 Prokaryotes have cell walls, which maintain cell
shape, protect the cell, and prevent 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
 Archaeal cell walls contain polysaccharides and
proteins but lack peptidoglycan
© 2016 Pearson
 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
© 2016 Pearson Education, Inc.
Figure 24.7
(a) Gram-positive bacteria
(b) Gram-negative
bacteria
Carbohydrate portion
of lipopolysaccharide
Cell
wall
Peptidoglycan
layer
Plasma
membrane
Outer
membrane
Cell
wall Peptidoglycan
layer
Plasma membrane
Gram-positive
bacteria
Gram-negative
bacteria
10 mm
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Figure 24.7-1
(a) Gram-positive bacteria
Cell
wall
Peptidoglycan
layer
Plasma
membrane
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Figure 24.7-2
(b) Gram-negative
bacteria
Carbohydrate portion
of lipopolysaccharide
Outer
membrane
Cell
wall Peptidoglycan
layer
Plasma membrane
© 2016 Pearson Education, Inc.
Figure 24.7-3
Gram-positive
bacteria
Gram-negative
bacteria
10 mm
© 2016 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 and allows them to
adhere to the substrate or each other
© 2016 Pearson Education, Inc.
Figure 24.8
Bacterial
cell wall
Bacterial
capsule
Tonsil
cell
200 nm
© 2016 Pearson Education, Inc.
 Some bacteria develop resistant cells called
endospores when they lack water or essential
nutrients
 Some prokaryotes stick to the substrate or each
other using hairlike appendages called fimbriae
 Pili (or sex pili) are longer than fimbriae and allow
prokaryotes to exchange DNA
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Figure 24.9
Fimbriae
1 mm
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Motility
 In a heterogeneous environment, many bacteria
exhibit taxis, the ability to move toward or away
from a stimulus
 For example, some prokaryotes exhibit chemotaxis,
movement toward or away from a chemical stimulus
© 2016 Pearson
 Many prokaryotes have flagella to facilitate
movement
 Flagella of bacteria, archaea, and eukaryotes are
composed of different proteins and likely evolved
independently
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Figure 24.10
Flagellum
Filament
Hook
Motor
Cell wall
Plasma
membrane
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Rod
Peptidoglycan
layer
20 nm
Figure 24.10-1
20 nm
Hook
Motor
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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
© 2016 Pearson
Internal Organization and DNA
 The cells of prokaryotes are structurally simpler
than those of eukaryotes
 Prokaryotic cells lack complex compartmentalization
 Some prokaryotes do have specialized membranes
that perform metabolic functions
 These are usually infoldings of the plasma
membrane
© 2016 Pearson
Figure 24.11
1 mm
0.2 mm
Respiratory
membrane
Thylakoid
membranes
(a) Aerobic prokaryote
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(b) Photosynthetic prokaryote
Figure 24.11-1
0.2 mm
Respiratory
membrane
(a) Aerobic prokaryote
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Figure 24.11-2
1 mm
Thylakoid
membranes
(b) Photosynthetic prokaryote
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 The prokaryotic genome has less DNA than the
eukaryotic genome
 Most of the genome consists of a single circular
chromosome
 The genetic material is not enclosed inside a
membrane; it is located in the nucleoid region
 Some species of bacteria also have smaller rings of
DNA called plasmids
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Figure 24.12
Chromosome
Plasmids
1 mm
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 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
© 2016 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 obtain carbon from organic nutrients
© 2016 Pearson
 Energy and carbon sources are combined to give
four major modes of nutrition




Photoautotrophy
Chemoautotrophy
Photoheterotrophy
Chemoheterotrophy
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Table 24.1
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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 use O2 if it is available, but
can survive without it
© 2016 Pearson
Nitrogen Metabolism
 Nitrogen is essential for the production of amino
acids and nucleic acids in all organisms
 Prokaryotes can metabolize nitrogen in a variety of
ways
 In nitrogen fixation, some prokaryotes convert
atmospheric nitrogen (N2) to ammonia (NH3)
© 2016 Pearson
Metabolic Cooperation
 Some prokaryotic cells cooperate to make use of
otherwise unavailable resources
 In the cyanobacterium Anabaena, photosynthetic
cells and nitrogen-fixing cells called heterocysts (or
heterocytes) exchange metabolic products
 Cooperation is necessary because the oxygen
produced by photosynthesis disrupts nitrogen
fixation
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Figure 24.13
Photosynthetic
cells
Heterocyst
20 mm
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 Metabolic cooperation between different prokaryotic
species occurs in surface-coating colonies called
biofilms
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Reproduction
 Many prokaryotes reproduce rapidly by binary
fission, a process by which one cell divides into two
 Key features of prokaryotic biology allow them to
divide quickly
 They are small
 They reproduce by binary fission
 They have short generation times
© 2016 Pearson
Adaptations of Prokaryotes: A Summary
 The ongoing success of prokaryotes is primarily the
result of physiological and metabolic diversification
 Metabolic diversification of prokaryotes was the first
great wave of adaptive radiation in the history of life
© 2016 Pearson
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
© 2016 Pearson
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 genetic diversity allows for rapid evolution
 Prokaryotes are not “primitive” but are highly
evolved
© 2016 Pearson
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
5,000
10,000 15,000
Generation
20,000
Data from V. S. Cooper and R. E. Lenski, The population genetics of ecological
specialization in evolving Escherichia coli populations, Nature 407:736–739 (2000).
© 2016 Pearson Education, Inc.
Figure 24.14-1
Experiment
Daily serial transfer
0.1 mL
(population sample)
Old tube
(discarded
after
transfer)
© 2016 Pearson Education, Inc.
New tube
(9.9 mL
growth
medium)
Figure 24.14-2
Population growth rate
(relative to ancestral
population)
Results
1.8
1.6
1.4
1.2
1.0
0
5,000
15,000
10,000
Generation
20,000
Data from V. S. Cooper and R. E. Lenski, The population genetics of ecological
specialization in evolving Escherichia coli populations, Nature 407:736–739 (2000).
© 2016 Pearson Education, Inc.
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
© 2016 Pearson
Transformation and Transduction
 Some prokaryotic cells can take up and incorporate
foreign DNA from the surrounding environment in a
process called transformation
 Transduction is the movement of genes between
prokaryotic cells by phages (viruses that infect
bacteria)
© 2016 Pearson
Figure 24.15-s1
Phage DNA
Phage infects bacterial
donor cell with A+ and B+
alleles.
A+ B+
Donor cell
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Figure 24.15-s2
Phage DNA
Phage infects bacterial
donor cell with A+ and B+
alleles.
A+ B+
Donor cell
Phage DNA is
replicated and
proteins synthesized.
© 2016 Pearson Education, Inc.
A+
B+
Figure 24.15-s3
Phage DNA
Phage infects bacterial
donor cell with A+ and B+
alleles.
A+ B+
Donor cell
Phage DNA is
replicated and
proteins synthesized.
Fragment of DNA with
A+ allele is packaged
within a phage capsid.
© 2016 Pearson Education, Inc.
A+
B+
A+
Figure 24.15-s4
Phage DNA
Phage infects bacterial
donor cell with A+ and B+
alleles.
A+ B+
Donor cell
Phage DNA is
replicated and
proteins synthesized.
A+
B+
Fragment of DNA with
A+ allele is packaged
within a phage capsid.
A+
Phage with
allele
infects bacterial
recipient cell.
A+
Crossing over
A+
A-
B-
Recipient
cell
© 2016 Pearson Education, Inc.
Figure 24.15-s5
Phage DNA
Phage infects bacterial
donor cell with A+ and B+
alleles.
A+ B+
Donor cell
Phage DNA is
replicated and
proteins synthesized.
A+
B+
Fragment of DNA with
A+ allele is packaged
within a phage capsid.
A+
A+
Crossing over
Phage with
allele
infects bacterial
recipient cell.
Incorporation of phage
DNA creates recombinant
with genotype A+B-.
© 2016 Pearson Education, Inc.
A+
A-
B-
Recipient
cell
Recombinant
cell
A+
B–
Conjugation and Plasmids
 Conjugation is a process by which genetic material
is transferred directly between prokaryotic cells
 In bacteria, the DNA transfer is one way
 For example, in E. coli, the donor cell attaches to a
recipient by a pilus, pulls it closer, and transfers DNA
© 2016 Pearson
Figure 24.16
1 mm
Pilus
© 2016 Pearson Education, Inc.
 The F factor is a piece of DNA required for the
production of pili
 It may be present in a plasmid or the chromosome
 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 transferred during conjugation
© 2016 Pearson Education, Inc.
Figure 24.17-s1
F plasmid
Bacterial
chromosome
F+ cell
(donor)
Mating
bridge
F– cell
(recipient)
Bacterial
chromosome
One strand of
F+ cell plasmid
DNA breaks at
arrowhead.
© 2016 Pearson Education, Inc.
Figure 24.17-s2
F plasmid
Bacterial
chromosome
F+ cell
(donor)
Mating
bridge
F– cell
(recipient)
Bacterial
chromosome
One strand of
F+ cell plasmid
DNA breaks at
arrowhead.
© 2016 Pearson Education, Inc.
Broken strand
peels off and
enters F– cell.
Figure 24.17-s3
F plasmid
Bacterial
chromosome
F+ cell
(donor)
Mating
bridge
F– cell
(recipient)
Bacterial
chromosome
One strand of
F+ cell plasmid
DNA breaks at
arrowhead.
© 2016 Pearson Education, Inc.
Broken strand
peels off and
enters F– cell.
Donor and
recipient cells
synthesize
complementary
DNA strands.
Figure 24.17-s4
F plasmid
Bacterial
chromosome
F+ cell
(donor)
F+
cell
Mating
bridge
F– cell
(recipient)
F+
cell
Bacterial
chromosome
One strand of
F+ cell plasmid
DNA breaks at
arrowhead.
© 2016 Pearson Education, Inc.
Broken strand
peels off and
enters F– cell.
Donor and
recipient cells
synthesize
complementary
DNA strands.
Recipient cell
is now a
recombinant
F+ cell.
 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
© 2016 Pearson Education, Inc.
R Plasmids and Antibiotic Resistance
 Genes for antibiotic resistance are often 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
© 2016 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
© 2016 Pearson
An Overview of Prokaryotic Diversity
 The application of molecular systematics has led to
dramatic revisions of the prokaryote phylogeny
 For example, the use of molecular systematics led to
the splitting of prokaryotes into Bacteria and Archaea
© 2016 Pearson
Figure 24.18
Euryarchaeotes
Crenarchaeotes
UNIVERSAL
ANCESTOR
Nanoarchaeotes
Domain Archaea
Korarchaeotes
Domain
Eukarya
Eukaryotes
Proteobacteria
Spirochetes
Cyanobacteria
Gram-positive
bacteria
© 2016 Pearson Education, Inc.
Domain Bacteria
Chlamydias
 The use of rapid sequencing techniques, such as
polymerase chain reaction (PCR), adds new
branches to the tree of life each year
 Only a tiny fraction of prokaryote diversity has been
identified and described thus far
© 2016 Pearson Education, Inc.
 Horizontal gene transfer has played a key role in
the evolution of prokaryotes
 Such gene transfers obscure the phylogenetic
relationships among prokaryote lineages
© 2016 Pearson Education, Inc.
Bacteria
 Bacteria include the vast majority of prokaryotes
familiar to most people
 Every major mode of nutrition and metabolism is
represented among bacteria
 A wide diversity of nutritional modes can be found
even within small taxonomic groups
© 2016 Pearson
Video: Tubeworms
© 2016 Pearson Education, Inc.
Figure 24.UN01
Eukarya
Archaea
Bacteria
© 2016 Pearson Education, Inc.
 Proteobacteria is a clade of gram-negative bacteria
with diverse metabolic and nutritional modes
 It has been divided into five subgroups (alpha, beta,
gamma, delta, and epsilon proteobacteria) based
on molecular relationships
© 2016 Pearson Education, Inc.
Figure 24.19-1
Alpha subgroup
Thiomargarita
namibiensis (LM)
© 2016 Pearson Education, Inc.
Delta subgroup
200 mm
Gamma subgroup
Chondromyces
crocatus (SEM)
1 mm
Nitrosomonas
(TEM)
Epsilon subgroup
2 mm
Rhizobium (arrows)
(TEM)
2.5 mm
Proteobacteria
300 mm
Alpha
Beta
Gamma
Delta
Epsilon
Beta subgroup
Helicobacter pylori
(TEM)
Figure 24.19-1a
Alpha
Beta
Gamma
Delta
Epsilon
© 2016 Pearson Education, Inc.
Proteobacteria
 Many species in the subgroup alpha
proteobacteria are closely associated with
eukaryotic hosts
 For example, Rhizobium forms root nodules in
legumes and fixes atmospheric N2
 Scientists use Agrobacterium to transfer foreign
DNA into crop plants
 Aerobic alpha proteobacteria may have given rise to
mitochondria through endosymbiosis
© 2016 Pearson Education, Inc.
Figure 24.19-1b
Alpha subgroup
2.5 mm
Rhizobium (arrows)
inside a root cell of a
legume (TEM)
© 2016 Pearson Education, Inc.
 Members of the subgroup beta proteobacteria
have diverse nutritional modes
 For example, Nitrosomonas participates in soil
nitrification by oxidizing ammonium (NH4+) and
producing nitrite (NO2–)
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Figure 24.19-1c
Beta subgroup
1 mm
Nitrosomonas
(colorized TEM)
© 2016 Pearson Education, Inc.
 The subgroup gamma proteobacteria includes
autotrophs and heterotrophs
 For example, Thiomargarita namibiensis is an
autotroph that obtains energy from H2S
 Some heterotrophic members of this group are
pathogenic
 For example, Salmonella causes food poisoning, and
Vibrio cholerae causes cholera
 Escherichia coli is a common heterotrophic gamma
proteobacteria that is not normally pathogenic
© 2016 Pearson Education, Inc.
Figure 24.19-1d
Gamma subgroup
200 mm
Thiomargarita
namibiensis containing
sulfur wastes (LM)
© 2016 Pearson Education, Inc.
 The subgroup delta proteobacteria includes the
slime-secreting myxobacteria and bdellovibrios, a
bacteria that attacks other bacteria
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Figure 24.19-1e
Delta subgroup
300 mm
Fruiting bodies of
Chondromyces crocatus,
a myxobacterium (SEM)
© 2016 Pearson Education, Inc.
 Most species in the subgroup epsilon
proteobacteria are pathogenic
 For example, Helicobacter pylori causes stomach
ulcers
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Figure 24.19-1f
Epsilon subgroup
2 mm
Helicobacter pylori
(colorized TEM)
© 2016 Pearson Education, Inc.
 Chlamydias are disease-causing parasites that can
only live within animal host cells
 For example, Chlamydia trachomatis causes
blindness and the sexually transmitted disease,
nongonococcal urethritis
© 2016 Pearson Education, Inc.
Figure 24.19-2a
Chlamydias
2.5 mm
Chlamydia (arrows) inside an
animal cell (colorized TEM)
© 2016 Pearson Education, Inc.
 Spirochetes are helical gram-negative
heterotrophs
 Many species are free-living, but some are parasitic
 For example, Treponema pallidum causes syphilis,
and Borrelia burgdorferi causes Lyme disease
© 2016 Pearson Education, Inc.
Figure 24.19-2b
Spirochetes
5 mm
Leptospira, a spirochete
(colorized TEM)
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 Cyanobacteria are gram-negative photoautotrophs
that generate O2 through plantlike photosynthesis
 Plant chloroplasts likely evolved from cyanobacteria
by the process of endosymbiosis
 Cyanobacteria are common members of the
phytoplankton in marine and freshwater
communities
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Figure 24.19-2c
Cyanobacteria
40 mm
Oscillatoria, a filamentous
cyanobacterium
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 Gram-positive bacteria include





Actinomycetes, many of which are soil decomposers
Streptomyces, which are a source of antibiotics
Bacillus anthracis, the cause of anthrax
Clostridium botulinum, the cause of botulism
Staphylococcus and Streptococcus, which can be
pathogenic
 Mycoplasmas, which are the smallest known cells
and the only bacteria lacking a cell wall
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Figure 24.19-2d
Gram-positive bacteria
5 mm
Streptomyces, the source of many
antibiotics (SEM)
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Figure 24.19-2e
Gram-positive bacteria
2 mm
Hundreds of mycoplasmas
covering a human fibroblast cell
(colorized SEM)
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Figure 24.19-2
Chlamydia (arrows)
(TEM)
Cyanobacteria
5 mm
Leptospira
(TEM)
Oscillatoria
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2 mm
5 mm
Gram-positive bacteria
Streptomyces
(SEM)
40 mm
Spirochetes
2.5 mm
Chlamydias
Mycoplasmas
(SEM)
Archaea
 Archaea share some traits in common with bacteria
and others with eukaryotes
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Figure 24.UN02
Eukarya
Archaea
Bacteria
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Table 24.2-1
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Table 24.2-2
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 Some archaea live in extreme environments and
are called extremophiles
 Extreme halophiles either tolerate or require a
highly saline environment
 For example, members of the genus Halobacterium
cannot survive if salinity drops below 9%
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Video: Cyanobacteria (Oscillatoria)
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 Extreme thermophiles thrive in very hot
environments
 For example, members of the genus Sulfolobus live
in hot springs with temperatures up to 90°C
 Many archaea live in more moderate environments
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Figure 24.20
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 Methanogens are strict anaerobes that produce
methane as a waste product
 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 mm
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Figure 24.21-1
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Figure 24.21-2
2 mm
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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
 The role of prokaryotes in the biosphere is essential
to the survival of many other species
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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
 For example, some chemoheterotrophic prokaryotes
are decomposers, organisms that break down dead
organic materials and release mineral nutrients
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 Some prokaryotes can convert molecules into forms
that can be taken up by other organisms
 For example, some species can fix atmospheric
nitrogen (N2) into forms available to plants
 Prokaryotes can also “immobilize” or decrease the
availability of plant 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 24.22-1
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
 These symbiotic relationships increase the fitness of
one or both organisms
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 In mutualism, both 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
carried by ticks
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Figure 24.24
5 mm
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Figure 24.24-1
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Figure 24.24-2
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Figure 24.24-3
5 mm
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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, and the
DNA polymerase from Pyrococcus furiosus is used in
the PCR technique
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 Experimental treatment of human cells with the
prokaryotic CRISPR-Cas9 system has shown
promising results for the treatment of HIV
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Figure 24.25
(a) Control cells
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(b) Experimental cells
Figure 24.25-1
(a) Control cells
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Figure 24.25-2
(b) Experimental cells
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 Some bacteria can be used to make natural,
biodegradable plastics
 Others have been engineered to produce ethanol
from plant sources and agricultural and municipal
wastes
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Figure 24.26
(b)
(a)
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Figure 24.26-1
(a)
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Figure 24.26-2
(b)
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 Prokaryotes are also used in bioremediation, the
use of organisms to remove pollutants from the
environment
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Figure 24.27
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Figure 24.UN03-1
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Figure 24.UN03-2
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Figure 24.UN04
Fimbriae
Cell wall
Circular
chromosome
Capsule
Pilus
Internal
organization
Flagella
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Figure 24.UN05
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Figure 24.UN06
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Figure 24.UN06-1
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Figure 24.UN06-2
© 2016 Pearson Education, Inc.