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Chapter 27
Prokaryotes 原核生物
張學偉 助理教授
生物醫學暨環境生物學系
[email protected]
PowerPoint Lectures for
Biology, Seventh第一教學大樓913室
Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Key Terms -1
• biofilms 生物膜 - Cells in a colony secrete signaling
molecules to recruit nearby cells, causing the colony to
grow.
• bioremediation - any process that uses microorganisms
or their enzymes to return the natural environment altered
by contaminants to its original condition.
• endospore 內孢子 - A cell replicates its chromosome and
surrounds one chromosome with a durable wall.
• fimbriae, pili - surface appendages of bacteria.
• horizontal gene transfer 平行基因傳遞 - also Lateral
gene transfer, is any process in which an organism
transfers genetic material to another cell that is not its
offspring.
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Key Terms - 2
• nutrition 營養- based on how they obtain energy and
carbon to build the organic molecules that make up their
cells .
• peptidoglycan - a polymer of modified sugars crosslinked by short polypeptides
• -Philes “lovers”
• phylogenetics 系統發生學 - is the study of evolutionary
relatedness among various groups of organisms.
• plasmids 質體 - smaller rings of DNA in prokaryotes.
• symbiosis - host & symbiont.
• taxis 驅性 - movement toward or away from a stimulus
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Lecture Outline-1
• Prokaryotes were the earliest organisms on Earth.
• Today, they still dominate the biosphere.
• Their collective biomass outweighs all eukaryotes
combined at least tenfold.
• Prokaryotes are wherever there is life.
• They thrive in habitats that are too cold, too hot,
too salty, too acidic, or too alkaline for any
eukaryote.
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Lecture Outline-2
• Prokaryotes have even been discovered in rocks
two miles below the surface of the Earth.
• Why have these organisms dominated the
biosphere since the origin of life on Earth?
• Prokaryotes display diverse adaptations that allow
them to inhabit many environments.
• They have great genetic diversity.
• Prokaryotes are classified into two domains,
Bacteria and Archaea, which differ in structure,
physiology and biochemistry.
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• Overview: They’re (Almost) Everywhere!
• Most prokaryotes are microscopic
– But what they lack in size they more than
make up for in numbers.
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• Prokaryotes thrive almost everywhere
– Including places too acidic, too salty, too cold,
or too hot for most other organisms
Hot water of a
Nevada geyser
Figure 27.1
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• Biologists are discovering
– That these organisms have an astonishing
genetic diversity
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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
– most common
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- cell wall.
– maintains cell shape,
– provides physical protection
– 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
Cell wall
Capsule
Figure 27.4
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• Capsules allow cells to adhere to their
substratum.
• They may increase resistance to host defenses.
• They glue together the cells of those
prokaryotes that live as colonies.
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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 are usually
more numerous and
shorter than pili
Fimbriae
200 nm
Figure 27.5
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• Fimbriae are usually more numerous and
shorter than pili.
• These structures can fasten pathogenic
bacteria to the mucous membranes of the host.
• Sex pili are specialized for holding two
prokaryote cells together long enough to
transfer DNA during conjugation.
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Conjugation: plasmid-directed transfer of DNA from one cell
to another.
補充
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Motility
• Most motile bacteria propel themselves by flagella
Flagellum
Filament
50 nm
Cell wall
Hook
Basal apparatus
Figure 27.6
Plasma
membrane
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27.6 Salmonella Flagella
• movie
Some species can move at speeds exceeding
50 m/sec, about 100 times their body length per
second.
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–structurally and functionally different
bwteen prokayotic & eukaryotic flagella
Fig. 7-?
Eukaryotic flagellum or cillum
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• In a heterogeneous environment, many
bacteria exhibit taxis
– The ability to move toward or away from
certain stimuli
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Internal and Genomic Organization
• 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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• Some species of bacteria
– Also have smaller rings of DNA called
plasmids
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Reproduction and Adaptation
• Prokaryotes reproduce quickly by binary fission
– And can divide every 1–3 hours
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• Many prokaryotes form endospores
– Which can remain viable in harsh conditions for
centuries
– When the environment becomes more hospitable,
the endospore absorbs water and resumes growth.
– Sterilization in an autoclave kills endospores by
heating them to 120°C under high pressure.
Endospore
Figure 27.9
0.3 m
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• Rapid reproduction and horizontal gene
transfer
– Facilitate the evolution of prokaryotes to
changing environments
Lacking meiotic sex, mutation is the major source
of genetic variation in prokaryotes.
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Horizontal gene transfer
• Conjugation can permit exchange of a
plasmid containing a few genes or large groups
of genes.
併入
• Once the transferred genes are incorporated
into the prokaryote’s genome, they are subject
to natural selection.
• Horizontal gene transfer is a major force in the
long-term evolution of pathogenic bacteria.
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• Concept 27.2: A great diversity of nutritional and
metabolic adaptations have evolved in prokaryotes
– Species that use light energy are phototrophs.
– Species that obtain energy from chemicals in
their environment are chemotrophs.
– Organisms that need only CO2 as a carbon
source are autotrophs. [自營]
– Organisms that require at least one organic
nutrient as a carbon source are heterotrophs. [異
營]
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• Photoautotrophs are photosynthetic
organisms that harness light energy to drive
the synthesis of organic compounds from
carbon dioxide.
– Among the photoautotrophic prokaryotes are
the cyanobacteria.
– Among the photosynthetic eukaryotes are
plants and algae.
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• Chemoautotrophs need only CO2 as a
carbon source, but they obtain energy by
oxidizing inorganic substances, rather than
light.
– These substances include hydrogen sulfide
(H2S), ammonia (NH3), and ferrous ions (Fe2+)
among others.
– This nutritional mode is unique to prokaryotes.
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• Photoheterotrophs use light to generate
ATP but obtain their carbon in organic form.
– This mode is restricted to prokaryotes.
• Chemoheterotrophs must consume organic
molecules for both energy and carbon.
– This nutritional mode is found widely in
prokaryotes, protists, fungi, animals, and even
some parasitic plants.
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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
– nitrogen fixation
– Some prokaryotes convert atmospheric
nitrogen to ammonia
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Metabolic Cooperation
• 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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27.10 Oscillatoria 顫藻屬
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• In some prokaryotic species
– Metabolic cooperation occurs in surfacecoating colonies called biofilms
1 m
colored
SEM for
dental
plaque
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 (phyle = tribe, race; genesis = birth)
– Is allowing systematists to identify major new
clades
Carl Woese and his colleagues used small-subunit
ribosomal RNA (SSU-rRNA) as a marker for
evolutionary relationships.
Microbiologists have since analyzed larger
amounts of genetic data, including whole genomes
of some species.
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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
Two important lessons from studies of prokaryotic phylogeny
• One is that the genetic diversity of prokaryotes
is immense.
 Every year, new prokaryotes are identified that add
major new branches to the tree of life.
• Another important lesson is the significance of
horizontal gene transfer in the evolution of
prokaryotes.
 As a result, significant portions of the genomes of many
prokaryotes are actually mosaics of genes imported from
other species.
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5 major groups of bacteria
• Proteobacteria
2.5 m
Rhizobium (arrows) inside a
root cell of a legume (TEM)
Chlamydia (arrows) inside an
animal cell (colorized TEM)
5 m
Nitrosomonas (colorized TEM)
Chlamydias,
spirochetes,
Gram +bact.
cyanobacteria
Leptospira, a spirochete
(colorized TEM)
Hundreds of mycoplasmas
Streptomyces, the source of
covering a human fibroblast cell
many antibiotics (colorized SEM) (colorized SEM)
Bdellovibrio bacteriophorus
Attacking a larger bacterium
(colorized TEM)
50 m
Fruiting bodies of
Chondromyces crocatus,
a myxobacterium (SEM)
1 m
5 m
Chromatium; the small
globules are sulfur wastes (LM)
Helicobacter pylori (colorized TEM).
Figure 27.13 Figure 27.13
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Two species of Oscillatoria,
filamentous cyanobacteria (LM)
Bacteria
• The two largest groups are
– The proteobacteria and the Gram-positive
bacteria
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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
Pyrococcus furiosus is as the source of DNA
polymerase for the polymerase chain reaction (PCR).
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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
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• All known extreme halophiles and
methanogens, plus a few extreme thermophiles,
are members of a clade called Euryarchaeota.
• Most thermophilic species belong to a second
clade, Crenarchaeota.
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• Concept 27.4: Prokaryotes play crucial roles in
the biosphere
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
• Nitrogen-fixing prokaryotes add usable nitrogen
to the environment
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Symbiotic Relationships
• In mutualism, both symbionts benefit.
Organ haboring bioluminescent bact.
Figure 27.15
• In commensalism, one symbiont receives
benefits while the other is not harmed or
helped by the relationship.
• In parasitism, one symbiont, the parasite,
benefits at the expense of the host.
Prokaryotes are involved in all three categories of
symbiosis with eukaryotes.
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• Concept 27.5: Prokaryotes have both harmful
and beneficial impacts on humans
• Pathogenic Prokaryotes  Prokaryotes cause about
half of all human diseases, e.g., Lyme disease.
Figure 27.16
5 µm
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• Pathogenic prokaryotes typically cause disease
– By releasing exotoxins or endotoxins
• Exotoxins are proteins secreted by
prokaryotes.
• Exotoxins can produce disease symptoms even if the prokaryote is
not present.
– Clostridium botulinum, which grows anaerobically in improperly
canned foods, produces an exotoxin that causes botulism.類桿菌中毒
– An exotoxin produced by Vibrio cholerae causes cholera. 霍亂
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• Endotoxins are components of the outer
membranes of some gram-negative bacteria.
– Salmonella typhi, which are not normally
present in healthy animals, causes typhoid
傷寒症
fever.
– Other Salmonella species, including some
that are common in poultry, cause food
poisoning.
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Education,Education,
Inc. publishing
as Benjamin
Cummings
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2002 Pearson
Inc.,
publishing
as Benjamin
Cummings
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
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• Prokaryotes are also major tools in
– Mining (recovery metal from ores)
– The synthesis of vitamins
– Production of antibiotics, hormones, and other
products
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Summary-1
A. Structural, Functional, and Genetic Adaptations
Contribute to Prokaryotic Success
1. Prokaryotes are small.
2. Nearly all prokaryotes have a cell wall external to the
plasma membrane.
3. Many prokaryotes are motile.
4. The cellular and genomic organization of prokaryotes is
fundamentally different from that of eukaryotes.
5. Populations of prokaryotes grow and adapt rapidly.
B. Nutritional and Metabolic Diversity
1. A great diversity of nutritional and metabolic adaptations
have evolved in prokaryotes.
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Summary-2
C. A Survey of Prokaryotic Diversity
1. Molecular systematics is leading to a phylogenetic
classification of prokaryotes.
2. Researchers are identifying a great diversity of archaea
in extreme environments and in the oceans.
D. The Ecological Impact of Prokaryotes
1. Prokaryotes are indispensable links in the recycling of
chemical elements in ecosystems.
2. Many prokaryotes are symbiotic.
3. Some prokaryotes are human pathogens.
4. Humans use prokaryotes in research and technology.
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