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Chapter 27
Prokaryotes
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Overview: They’re (Almost) Everywhere!
• Most prokaryotes are microscopic
– But what they lack in size they more than
make up for in numbers
• The number of prokaryotes in a single handful
of fertile soil
– Is greater than the number of people who have
ever lived
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• Prokaryotes thrive almost everywhere
– Including places too acidic, too salty, too cold,
or too hot for most other organisms
Figure 27.1
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• Concept 27.1: Structural, functional, and
genetic adaptations contribute to prokaryotic
success
• Most prokaryotes are unicellular
– Although some species form colonies
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• Prokaryotic cells have a variety of shapes
– The three most common of which are spheres
(cocci), rods (bacilli), and spirals
1 m
Figure 27.2a–c (a) Spherical (cocci)
2 m
(b) Rod-shaped (bacilli)
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5 m
(c) Spiral
Cell-Surface Structures
• One of the most important features of nearly all
prokaryotic cells
– Is their cell wall, which maintains cell shape,
provides physical protection, and prevents the
cell from bursting in a hypotonic environment
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• Using a technique called the Gram stain
– Scientists can classify many bacterial species into
two groups based on cell wall composition, Grampositive and Gram-negative
Lipopolysaccharide
Cell wall
Peptidoglycan
layer
Cell wall
Outer
membrane
Peptidoglycan
layer
Plasma membrane
Plasma membrane
Protein
Protein
Grampositive
bacteria
Gramnegative
bacteria
20 m
(a) Gram-positive. Gram-positive bacteria have
a cell wall with a large amount of peptidoglycan
that traps the violet dye in the cytoplasm. The
alcohol rinse does not remove the violet dye,
which masks the added red dye.
Figure 27.3a, b
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(b) Gram-negative. Gram-negative bacteria have less
peptidoglycan, and it is located in a layer between the
plasma membrane and an outer membrane. The
violet dye is easily rinsed from the cytoplasm, and the
cell appears pink or red after the red dye is added.
• The cell wall of many prokaryotes
– Is covered by a capsule, a sticky layer of
polysaccharide or protein
200 nm
Capsule
Figure 27.4
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• Some prokaryotes have fimbriae and pili
– Which allow them to stick to their substrate or
other individuals in a colony
Fimbriae
200 nm
Figure 27.5
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Motility
• Most motile bacteria propel themselves by flagella
– Which are structurally and functionally different
from eukaryotic flagella
Flagellum
Filament
50 nm
Cell wall
Hook
Basal apparatus
Figure 27.6
Plasma
membrane
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• In a heterogeneous environment, many
bacteria exhibit taxis
– The ability to move toward or away from
certain stimuli
• Prokaryotic cells
– Usually lack complex compartmentalization
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• Some prokaryotes
– Do have specialized membranes that perform
metabolic functions
0.2 m
1 m
Respiratory
membrane
Thylakoid
membranes
Figure 27.7a, b
(a) Aerobic prokaryote
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(b) Photosynthetic prokaryote
• The typical prokaryotic genome
– Is a ring of DNA that is not surrounded by a
membrane and that is located in a nucleoid region
Chromosome
Figure 27.8
1 m
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Reproduction and Adaptation
• Prokaryotes reproduce quickly by binary fission
– And can divide every 1–3 hours
• Rapid reproduction and horizontal gene
transfer
– Facilitate the evolution of prokaryotes to
changing environments
– Increases rate of mutation that drives natural
selection
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• Many prokaryotes form endospores
– Which can remain viable in harsh conditions
for centuries
Endospore
0.3 m
Figure 27.9
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• Concept 27.2: A great diversity of nutritional
and metabolic adaptations have evolved in
prokaryotes
• Examples of all four models of nutrition are
found among prokaryotes
– Photoautotrophy
– Chemoautotrophy
– Photoheterotrophy
– Chemoheterotrophy
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• Major nutritional modes in prokaryotes
Table 27.1
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Metabolic Relationships to Oxygen
• Prokaryotic metabolism
– Also varies with respect to oxygen
• Obligate aerobes
– Require oxygen
• Facultative anaerobes
– Can survive with or without oxygen
• Obligate anaerobes
– Are poisoned by oxygen
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Nitrogen Metabolism
• Prokaryotes can metabolize nitrogen
– In a variety of ways
• In a process called nitrogen fixation
– Some prokaryotes convert atmospheric
nitrogen to ammonia
• Cooperation between prokaryotes
– Allows them to use environmental resources
they could not use as individual cells
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• In the cyanobacterium Anabaena
– Photosynthetic cells and nitrogen-fixing cells
exchange metabolic products
Photosynthetic
cells
Heterocyst
20 m
Figure 27.10
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• In some prokaryotic species
1 m
– Metabolic cooperation occurs in surfacecoating colonies called biofilms
Figure 27.11
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• Concept 27.3: Molecular systematics is
illuminating prokaryotic phylogeny
• Until the late 20th century
– Systematists based prokaryotic taxonomy on
phenotypic criteria
• Applying molecular systematics to the
investigation of prokaryotic phylogeny
– Has produced dramatic results
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Lessons from Molecular Systematics
• Molecular systematics
– Is leading to a phylogenetic classification of
prokaryotes
– Is allowing systematists to identify major new
clades
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• A tentative phylogeny of some of the major taxa of
prokaryotes based on molecular systematics
Domain
Archaea
Domain Bacteria
Proteobacteria
Figure 27.12
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Universal ancestor
Domain
Eukarya
Bacteria
• Diverse nutritional types
– Are scattered among the major groups of
bacteria
• The two largest groups are
– The proteobacteria and the Gram-positive
bacteria
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2.5 m
• Proteobacteria
1 m
Rhizobium (arrows) inside a
root cell of a legume (TEM)
0.5 m
Nitrosomonas (colorized TEM)
Fruiting bodies of
Chondromyces crocatus,
a myxobacterium (SEM)
5 m
10 m
Chromatium; the small
globules are sulfur wastes (LM)
2 m
Bdellovibrio bacteriophorus
Attacking a larger bacterium
(colorized TEM)
Figure 27.13
Helicobacter pylori (colorized TEM).
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2.5 m
• Chlamydias, spirochetes, Gram-positive
bacteria, and cyanobacteria
5 m
Chlamydia (arrows) inside an
animal cell (colorized TEM)
1 m
5 m
Leptospira, a spirochete
(colorized TEM)
50 m
Hundreds of mycoplasmas
Streptomyces, the source of
covering a human fibroblast cell
many antibiotics (colorized SEM) (colorized SEM)
Figure 27.13
Two species of Oscillatoria,
filamentous cyanobacteria (LM)
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Archaea
• Archaea share certaintraits with bacteria
– And other traits
with eukaryotes
Table 27.2
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• Some archaea
– Live in extreme environments
• Extreme thermophiles
– Thrive in very hot environments
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• Extreme halophiles
– Live in high saline environments
Figure 27.14
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• Methanogens
– Live in swamps and marshes
– Produce methane as a waste product
– Obligate anaerobes
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• Concept 27.4: Prokaryotes play crucial roles in
the biosphere
• Prokaryotes are so important to the biosphere
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 continual recycling of chemical elements
between the living and nonliving components
of the environment in ecosystems
• Chemoheterotrophic prokaryotes function as
decomposers
– Breaking down corpses, dead vegetation, and
waste products
• Nitrogen-fixing prokaryotes
– Add usable nitrogen to the environment
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Symbiotic Relationships
• Many prokaryotes
– Live with other organisms in symbiotic
relationships such as mutualism and
commensalism
Figure 27.15
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• Concept 27.5: Prokaryotes have both harmful
and beneficial impacts on humans
• Some prokaryotes are human pathogens
– But many others have positive interactions with
humans
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Pathogenic Prokaryotes
• Prokaryotes cause about half of all human
diseases
– Lyme disease is an example
Figure 27.16
5 µm
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• Pathogenic prokaryotes typically cause disease
– By releasing exotoxins or endotoxins
• Many pathogenic bacteria
– Are potential weapons of bioterrorism
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Prokaryotes in Research and Technology
• Experiments using prokaryotes
– Have led to important advances in DNA
technology
• Prokaryotes are also major tools in
– Mining
– The synthesis of vitamins
– Production of antibiotics, hormones, and other
products
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• Prokaryotes are the principal agents in
bioremediation
– The use of organisms to remove pollutants
from the environment
Figure 27.17
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