27 prokaryotes7th

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 27
Prokaryotes

• 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

• Prokaryotes thrive almost everywhere
– Including places too acidic, too salty, too cold,
or too hot for most other organisms
Figure 27.1

• Biologists are discovering
– That these organisms have an astonishing
genetic diversity

• Concept 27.1: Structural, functional, and
genetic adaptations contribute to prokaryotic
success
• Most prokaryotes are unicellular
– Although some species form colonies

• Prokaryotic cells have a variety of shapes
– The three most common of which are spheres
(cocci), rods (bacilli), and spirals
1 µm 2 µm 5 µm
(a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) SpiralFigure 27.2a–c

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

• Using a technique called the Gram stain
– Scientists can classify many bacterial species into
two groups based on cell wall composition, Gram-
positive and Gram-negative
(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.
(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.
Figure 27.3a, b
Peptidoglycan
layerCell wall
Plasma membrane
Protein
Gram-
positive
bacteria
20 µm
Outer
membrane
Peptidoglycan
layer
Plasma membrane
Cell wall
Lipopolysaccharide
Protein
Gram-
negative
bacteria

• The cell wall of many prokaryotes
– Is covered by a capsule, a sticky layer of
polysaccharide or protein
200 nm
Capsule
Figure 27.4

• Some prokaryotes have fimbriae and pili
– Which allow them to stick to their substrate or
other individuals in a colony
200 nm
Fimbriae
Figure 27.5

Motility
• Most motile bacteria propel themselves by flagella
– Which are structurally and functionally different
from eukaryotic flagella
Flagellum
Filament
HookCell wall
Plasma
membrane
Basal apparatus
50 nm
Figure 27.6

• In a heterogeneous environment, many
bacteria exhibit taxis
– The ability to move toward or away from
certain stimuli

Internal and Genomic Organization
• Prokaryotic cells
– Usually lack complex compartmentalization

• Some prokaryotes
– Do have specialized membranes that perform
metabolic functions
(a) Aerobic prokaryote (b) Photosynthetic prokaryote
0.2 µm 1 µm
Respiratory
membrane
Thylakoid
membranes
Figure 27.7a, b

• The typical prokaryotic genome
– Is a ring of DNA that is not surrounded by a
membrane and that is located in a nucleoid region
Figure 27.8
1 µm
Chromosome

• Some species of bacteria
– Also have smaller rings of DNA called
plasmids

Reproduction and Adaptation
• Prokaryotes reproduce quickly by binary fission
– And can divide every 1–3 hours

• Many prokaryotes form endospores
– Which can remain viable in harsh conditions
for centuries
Endospore
0.3 µm
Figure 27.9

• Rapid reproduction and horizontal gene
transfer
– Facilitate the evolution of prokaryotes to
changing environments

• 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

• Major nutritional modes in prokaryotes
Table 27.1

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

Nitrogen Metabolism
• Prokaryotes can metabolize nitrogen
– In a variety of ways
• In a process called nitrogen fixation
– Some prokaryotes convert atmospheric
nitrogen to ammonia

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
exchange metabolic products
Photosynthetic
cells
Heterocyst
20 µm
Figure 27.10

• In some prokaryotic species
– Metabolic cooperation occurs in surface-
coating colonies called biofilms
Figure 27.11
1µm

• 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

Lessons from Molecular Systematics
• Molecular systematics
– Is leading to a phylogenetic classification of
prokaryotes
– Is allowing systematists to identify major new
clades

• A tentative phylogeny of some of the major taxa of
prokaryotes based on molecular systematics
Figure 27.12
Domain Bacteria
Domain
Archaea
Domain
Eukarya
Alpha
Beta
Gamma
Epsilon
Delta
Proteobacteria
Chlamydias
Spirochetes
Cyanobacteria
Gram-positive
bacteria
Korarchaeotes
Euryarchaeotes
Crenarchaeotes
Nanoarchaeotes
Eukaryotes
Universal ancestor

Bacteria
• Diverse nutritional types
– Are scattered among the major groups of
bacteria
• The two largest groups are
– The proteobacteria and the Gram-positive
bacteria

• Proteobacteria
Chromatium; the small
globules are sulfur wastes (LM)
Fruiting bodies of
Chondromyces crocatus,
a myxobacterium (SEM)
Bdellovibrio bacteriophorus
Attacking a larger bacterium
(colorized TEM)
2.5µm
1µm0.5µm10µm
5µm
2µm
Figure 27.13
Rhizobium (arrows) inside a
root cell of a legume (TEM)
Nitrosomonas (colorized TEM)
Chromatium; the small
globules are sulfur wastes (LM)
Fruiting bodies of
Chondromyces crocatus,
a myxobacterium (SEM)
Bdellovibrio bacteriophorus
Attacking a larger bacterium
(colorized TEM)
Helicobacter pylori (colorized TEM).

• Chlamydias, spirochetes, Gram-positive
bacteria, and cyanobacteria
Chlamydia (arrows) inside an
animal cell (colorized TEM)
Leptospira, a spirochete
(colorized TEM)
Streptomyces, the source of
many antibiotics (colorized SEM)
Two species of Oscillatoria,
filamentous cyanobacteria (LM)
Hundreds of mycoplasmas
covering a human fibroblast cell
(colorized SEM)
2.5µm5µm5µm50µm
1µm
Figure 27.13

Archaea
• Archaea share certaintraits with bacteria
– And other traits
with eukaryotes
Table 27.2

• Some archaea
– Live in extreme environments
• Extreme thermophiles
– Thrive in very hot environments

• Extreme halophiles
– Live in high saline environments
Figure 27.14

• Methanogens
– Live in swamps and marshes
– Produce methane as a waste product

• 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

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

Symbiotic Relationships
• Many prokaryotes
– Live with other organisms in symbiotic
relationships such as mutualism and
commensalism
Figure 27.15

• Other types of prokaryotes
– Live inside hosts as parasites

• 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

Pathogenic Prokaryotes
• Prokaryotes cause about half of all human
diseases
– Lyme disease is an example
5 µm
Figure 27.16

• Pathogenic prokaryotes typically cause disease
– By releasing exotoxins or endotoxins
• Many pathogenic bacteria
– Are potential weapons of bioterrorism

Prokaryotes in Research and Technology
• Experiments using prokaryotes
– Have led to important advances in DNA
technology

• Prokaryotes are the principal agents in
bioremediation
– The use of organisms to remove pollutants
from the environment
Figure 27.17

• Prokaryotes are also major tools in
– Mining
– The synthesis of vitamins
– Production of antibiotics, hormones, and other
products

27 prokaryotes7th

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