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Prokaryotes
Chapter 27
•  They’re (almost) Everywhere!
•  Most prokaryotes are microscopic
Prokaryotes: Domains
Bacteria & Archaea
–  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
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•  Prokaryotes thrive almost everywhere
•  Biologists are discovering
–  Including places too acidic, too salty, too cold,
or too hot for most other organisms
–  These organisms have an astonishing genetic
diversity
–  Not too surprising, given their 3.5+ billion years
of evolution!
•  Structural, functional, and genetic adaptations
contribute to prokaryotic success
•  Most prokaryotes are unicellular
–  Although some species form colonies
Figure 27.1
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Domain Bacteria: a prokaryote
•  Prokaryotic cells have a variety of shapes
Fimbriae
Nucleoid
–  The three most common of which are spheres
(cocci), rods (bacilli), and spirals (spirilla)
Ribosomes
Plasma membrane
Bacterial
chromosome
(a) A typical
rod-shaped
bacterium
Cell wall
Capsule
Flagella
0.5 µm
(b) A thin section
through the
bacterium
Bacillus
coagulans (TEM)
1 µm
Figure 27.2a–c (a) Spherical (cocci)
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2 µm
(b) Rod-shaped (bacilli)
(c) Spiral
5 µm
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1
Cell-Surface Structures
The Gram Stain
•  One of the most important features of nearly all
prokaryotic cells
•  Allows scientists to classify many bacterial species
into two groups based on cell wall composition:
Gram-positive (clade?) and Gram-negative
–  Is their cell wall, which maintains cell shape,
provides physical protection, and prevents the
cell from bursting in a hypotonic environment
Lipopolysaccharide
Cell wall
Peptidoglycan
layer
Cell wall
Outer
membrane
Peptidoglycan
layer
Plasma membrane
Plasma membrane
Protein
Protein
Grampositive
bacteria
Gramnegative
bacteria
20 µm
(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.
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Streptococcus on tonsil cell
•  The cell wall of many prokaryotes
•  Some prokaryotes have fimbriae and pili
–  Is covered by a capsule, a sticky layer of
polysaccharide or protein
–  Which allow them to stick to their substrate or
other individuals in a colony
200 nm
Fimbriae
Capsule
200 nm
Figure 27.5
Figure 27.4
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Motility
•  Most motile bacteria propel themselves by flagella
–  Which are structurally and functionally different
from eukaryotic flagella
•  In a heterogeneous environment, many
bacteria exhibit taxis
–  The ability to move toward or away from
certain stimuli
Flagellum
Filament
50 nm
Cell wall
Hook
Basal apparatus
Figure 27.6
Plasma
membrane
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Internal and Genomic Organization
Escherichia coli cell and its chromosome
•  Most Prokaryotic cells lack complex compartmentalization
(membrane-bound organelles)
•  The typical prokaryotic genome
•  But some have specialized membranes that perform
metabolic functions (recall endosymbiotic theory)
0.2 µm
–  Is a ring of DNA that is not surrounded by a
membrane and that is located in a nucleoid region
1 µm
Chromosome
Respiratory
membrane
Thylakoid
membranes
Figure 27.7a, b
(a) Aerobic prokaryote
(b) Photosynthetic prokaryote
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Figure 27.8
1 µm
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Fig. 27-8
Chromosome
Plasmids
•  Some species of bacteria
–  Also have smaller rings of DNA called
plasmids
1 µm
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Reproduction and Adaptation
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Fig. 27-12
•  Prokaryotes reproduce quickly by binary fission
–  Every 1–3 hours (or faster: 20 min)
–  Asexual reproduction
•  Prokaryotes can exchange DNA: Horizontal
transfer - often via plasmids
Fig. 27-12
–  Conjugation: passing DNA between cells
–  Transformation: DNA can be acquired from the
environment
–  Transduction: DNA transfer via viruses
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Conjugation via Sex pilus
1 µm
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Fig. 27-13
Conjugation and the F factor (fertility)
Fertility (F) and Resistance (R) Plasmids
•  Rapid reproduction and horizontal gene transfer
F plasmid
Bacterial chromosome
F+ cell
–  Facilitate the evolution of prokaryotes to
changing environments
F+ cell
Mating
bridge
F– cell
–  Adaptations can readily be propagated within a
‘species’ and to other prokaryotes
F+ cell
Bacterial
chromosome
(a) Conjugation and transfer of an F plasmid
Hfr cell
A+
F factor
F– cell
A+
A+
A+
A–
Recombinant
F– bacterium
A–
A–
A+
•  E.g. R Plasmids spread anti-biotic resistance
A+
A–
(b) Conjugation and transfer of part of an Hfr bacterial chromosome
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Prokaryotes Exhibit Diverse Nutritional Modes
•  Many prokaryotes form endospores
–  Which can remain viable in harsh conditions
for centuries Bacillus anthracis
•  A great diversity of nutritional and metabolic
adaptations have evolved in prokaryotes
–  All major biochemical pathways
•  Examples of all four modes of nutrition are
found among prokaryotes
Endospore
–  Photoautotrophy
–  Chemoautotrophy
–  Photoheterotrophy
Figure 27.9
0.3 µm
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–  Chemoheterotrophy
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Prokaryotes Exhibit Diverse Nutritional Modes
Prokaryotes Exhibit Diverse Nutritional Modes
•  Phototrophs: energy from sun
•  All four possible modes of nutrition are found
among prokaryotes
•  Chemotrophs: energy from molecules
•  Autotrophs: able to build their own organic cds
•  Heterotrophs: require organic nutrient(s)
–  Photoautotrophy
–  Chemoautotrophy
–  Photoheterotrophy
–  Chemoheterotrophy
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Metabolic Relationships to Oxygen
•  Major nutritional modes in prokaryotes
•  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
Table 27.1
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Nitrogen Metabolism
Some Prokaryotes Exhibit Multicellularity
•  Prokaryotes can metabolize nitrogen
•  In the cyanobacterium Anabaena (and Nostoc)
–  In a variety of ways
•  In a process called nitrogen fixation
–  Photosynthetic cells and nitrogen-fixing cells
exchange metabolic products
–  Some prokaryotes convert atmospheric
nitrogen to ammonia
Photosynthetic
cells
Heterocyst
Figure 27.10
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20 µm
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Metabolic Cooperation
Metabolic Cooperation in Prokaryotes
•  Cooperation between prokaryotes
•  Surface-coating colonies called biofilms
–  Dental plaque
1 µm
–  Allows them to use environmental resources
they could not use as individual cells
Figure 27.11
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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Lessons from Molecular Systematics
Nanoarchaeotes
Domain
Eukarya
Eukaryotes
Korarchaeotes
Euryarchaeotes
Gram-positive
bacteria
Cyanobacteria
Spirochetes
Chlamydias
Epsilon
Delta
Beta
•  Molecular systematics
Crenarchaeotes
Domain
Archaea
Domain Bacteria
Proteobacteria
Alpha
–  Systematists based prokaryotic taxonomy on
phenotypic criteria: e.g. shape, gram stain,
nutritional mode
•  A tentative phylogeny of some of the major taxa of
prokaryotes based on molecular systematics
Gamma
•  Until the late 20th century
–  Is leading to a phylogenetic classification of
prokaryotes, and
–  Identification of major new clades
Universal ancestor
Figure 27.12
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Bacteria
•  Proteobacteria
α proteobacteria closest living relatives of
mitochondria
2.5 µm
•  Diverse nutritional types
–  Are scattered among the major groups of
bacteria
1 µm
Rhizobium (arrows) inside a
root cell of a legume (TEM)
•  The two largest groups are
Nitrosomonas (colorized TEM)
0.5 µm
–  The proteobacteria and the Gram-positive
bacteria
Fruiting bodies of
Chondromyces crocatus,
a myxobacterium (SEM)
5 µm
10 µm
Chromatium; the small
globules are sulfur wastes (LM)
2 µm
Bdellovibrio bacteriophorus
Attacking a larger bacterium
(colorized TEM)
Figure 27.13
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Helicobacter pylori (colorized TEM).
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Archaea
2.5 µm
•  Chlamydias, spirochetes, Gram-positive
bacteria, and cyanobacteria
•  Archaea share certain traits with bacteria
–  And other traits
with eukaryotes
5 µm
Chlamydia (arrows) inside an
animal cell (colorized TEM)
1 µm
5 µm
Leptospira, a spirochete
(colorized TEM)
50 µm
Hundreds of mycoplasmas
covering a human fibroblast cell
Streptomyces, the source of
many antibiotics (colorized SEM) (colorized SEM)
Figure 27.13
Two species of Oscillatoria,
filamentous cyanobacteria (LM)
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Table 27.2
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Some Archaea are ‘Extremophiles’
Archaea
•  Extremophiles ‘love’ extreme environments
•  Extreme halophiles
–  Live in extreme environments
–  Live in high saline environments
•  Extreme thermophiles
–  Thrive in very hot environments
•  e.g. Hydro-thermal vents
Figure 27.14
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Archaea
•  Methanogens
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Text Art 5.02
Prokaryotes are Superabundant; New Genomics:
Up to 50,000 species from Sargasso Sea
–  Live in swamps and marshes
–  Produce methane as a waste product
–  Obligate anaerobes
•  Archaeans are also found in ‘normal’
environments
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Ecology of Prokaryotes
Chemical Recycling
•  Prokaryotes play crucial roles in the biosphere
•  Prokaryotes play a major role
•  Prokaryotes are so important to the biosphere
that if they were to disappear
–  The prospects for any other life surviving would
be dim
•  e.g. Photosynthesis
–  The loss of Eukaryotes would not have such
an effect on Prokaryotes
–  In the continual recycling of chemical elements
between the living and nonliving components
of the environment in ecosystems
•  Many 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: Living together
Symbiotic Relationships
•  Some prokaryotes
•  Mutualism: light-producing bacteria live in
special organs of the flashlight fish
–  Live inside hosts as parasites or disease
agents
•  Some prokaryotes
–  Live with mutualistic relationships with their
hosts (both benefit):
•  Legumes (peas & beans) host nitrogenfixing bacteria in their roots
–  Others may be commensals (commensalism)
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Symbiotic Relationships
Figure 27.15
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Escherichia coli - some forms parasitic/pathogens
•  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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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Pathogenic Prokaryotes
•  Prokaryotes cause about half of all human
diseases
–  Lyme disease is an example
•  Pathogenic prokaryotes typically cause disease
–  By releasing exotoxins or endotoxins
•  Many pathogenic bacteria
–  Are potential weapons of bioterrorism
Figure 27.16
5 µm
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Prokaryotes in Research and Technology
•  Experiments using prokaryotes
–  Have led to important advances in DNA
technology
–  Escherichia coli makes insulin for diabetics!
•  Prokaryotes are the principal agents in
bioremediation
–  The use of organisms to remove pollutants
from the environment
Figure 27.17
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fig. 28-03a
Excavata
Diplomonads
Parabasalids
Euglenozoans
•  Prokaryotes are also major tools in
Dinoflagellates
Alveolates
Apicomplexans
Chromalveolata
–  Mining
Ciliates
Diatoms
Stramenopiles
–  The synthesis of vitamins
Golden algae
Brown algae
Oomycetes
Chlorarachniophytes
Forams
Radiolarians
Green
algae
Archaeplastida
Red algae
Chlorophytes
Charophyceans
Land plants
Amoebozoans
Slime molds
Gymnamoebas
Nucleariids
Sperm
Haploid (n)
Diploid (2n)
Key
“Bud”
Protonemata
Animals
1 Sporangia release spores.
Most fern species produce a single
type of spore that gives rise to a
bisexual gametophyte.
Key
Male
gametophyte
2 The haploid
protonemata
produce “buds”
that grow into
gametophytes.
Choanoflagellates
•  The life cycle of a fern
Raindrop
Spores develop into
threadlike protonemata.
Fungi
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•  The life cycle of a moss
1
Unikonta
Entamoebas
Opisthokonts
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Rhizaria
–  Production of antibiotics, hormones, and other
products
4 A sperm swims
through a film of
moisture to an
archegonium and
fertilizes the egg.
Antheridia
3 Most mosses have separate
male and female gametophytes,
with antheridia and archegonia,
respectively.
2 The fern spore
develops into a small,
photosynthetic gametophyte.
3 Although this illustration
shows an egg and sperm
from the same gametophyte,
a variety of mechanisms
promote cross-fertilization
between gametophytes.
Haploid (n)
Diploid (2n)
Antheridium
Spore
MEIOSIS
Young
gametophyte
“Bud”
Sporangium
Egg
Spores
Gametophore
Female
Archegonia
Meiosis occurs and haploid
spores develop in the sporangium gametophyte
of the sporophyte. When the
Rhizoid
sporangium lid pops off, the
peristome “teeth” regulate
6 The sporophyte grows a
gradual release of the spores. long stalk, or seta, that emerges
Seta
from the archegonium.
Archegonium
8
Peristome
Sporangium
MEIOSIS
Mature
Mature
sporophytes
sporophytes
Capsule
(sporangium)
Calyptra
Zygote
Mature
sporophyte
6 On the underside
of the sporophyte‘s
reproductive leaves
are spots called sori.
Each sorus is a
cluster of sporangia.
Embryo
Female
gametophytes
Young
5 The diploid zygote
sporophyte
develops into a
sporophyte embryo within
7 Attached by its foot, the
the archegonium.
sporophyte remains nutritionally
dependent on the gametophyte.
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FERTILIZATION
Sorus
FERTILIZATION
Archegonium
Capsule with
peristome (LM)
Sperm
Egg
Zygote
(within archegonium)
Foot
Figure 29.8
New
sporophyte
Sporangium
Gametophyte
Fiddlehead
Figure 29.12
4 Fern sperm use flagella
to swim from the antheridia
to eggs in the archegonia.
5 A zygote develops into a new
sporophyte, and the young plant
grows out from an archegonium
of its parent, the gametophyte.
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9