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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
PowerPoint® Lecture Presentations for
Biology Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Chapter 27Chapter 27
Bacteria and Archaea
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• Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms
• Most prokaryotes are microscopic, but what they lack in size they make up for in numbers
• There are more in a handful of fertile soil than the number of people who have ever lived
Overview: Masters of Adaptation
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• They have an astonishing genetic diversity
• Prokaryotes are divided into two domains: bacteria and archaea
Video: TubewormsVideo: Tubeworms
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Concept 27.1: Structural and functional adaptations contribute to prokaryotic success
• Most prokaryotes are unicellular, although some species form colonies
• Most prokaryotic cells are 0.5–5 µm, much smaller than the 10–100 µm 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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Fig. 27-2
(a) Spherical (cocci)
1 µm
(b) Rod-shaped (bacilli)
2 µm
(c) Spiral
5 µm
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Cell-Surface Structures
• An important feature 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
• Eukaryote cell walls are made of cellulose or chitin
• Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides
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• Archaea contain polysaccharides and proteins but lack peptidoglycan
• Using the Gram stain, scientists classify many bacterial species into Gram-positive and Gram-negative groups based on cell wall composition
• Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic, and they are more likely to be antibiotic resistant
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• Many antibiotics target peptidoglycan and damage bacterial cell walls
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Fig. 27-3
Cellwall
Peptidoglycanlayer
Plasma membrane
Protein
Gram-positivebacteria
(a) Gram-positive: peptidoglycan traps crystal violet.
Gram-negativebacteria
(b) Gram-negative: crystal violet is easily rinsed away, revealing red dye.
20 µm
Cellwall
Plasma membrane
Protein
Carbohydrate portionof lipopolysaccharide
Outermembrane
Peptidoglycanlayer
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Fig. 27-3a
Cellwall
Peptidoglycanlayer
Plasma membrane
Protein
(a) Gram-positive: peptidoglycan traps crystal violet.
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Fig. 27-3b
Cellwall Peptidoglycan
layerPlasma membrane
Protein
(b) Gram-negative: crystal violet is easily rinsed away, revealing red dye.
Outermembrane
Carbohydrate portionof lipopolysaccharide
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Fig. 27-3c
Gram-positivebacteria
Gram-negativebacteria
20 µm
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• A polysaccharide or protein layer called a capsule covers many prokaryotes
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Fig. 27-4
Capsule
200 nm
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• Some prokaryotes have fimbriae (also called attachment pili), which allow them to stick to their substrate or other individuals in a colony
• Sex pili are longer than fimbriae and allow prokaryotes to exchange DNA
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Fig. 27-5
Fimbriae
200 nm
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Motility
• Most motile bacteria propel themselves by flagella that 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
Video: Prokaryotic Flagella (Video: Prokaryotic Flagella (Salmonella typhimuriumSalmonella typhimurium))
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Fig. 27-6
Flagellum
Filament
Hook
Basal apparatus
Cell wall
Plasmamembrane
50 nm
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Fig. 27-6a
Cell wall
Filament
Hook
Basal apparatus
Plasmamembrane
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Fig. 27-6b
Prokaryotic flagellum (TEM)
50 nm
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Internal and Genomic Organization
• Prokaryotic cells usually lack complex compartmentalization
• Some prokaryotes do have specialized membranes that perform metabolic functions
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Fig. 27-7
(a) Aerobic prokaryote (b) Photosynthetic prokaryote
Thylakoidmembranes
Respiratorymembrane
0.2 µm 1 µm
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Fig. 27-7a
(a) Aerobic prokaryote
Respiratorymembrane
0.2 µm
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Fig. 27-7b
(b) Photosynthetic prokaryote
Thylakoidmembranes
1 µm
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• The prokaryotic genome has less DNA than the eukaryotic genome
• Most of the genome consists of a circular chromosome
• Some species of bacteria also have smaller rings of DNA called plasmids
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Fig. 27-8
Chromosome Plasmids
1 µm
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• The typical prokaryotic genome is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region
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Reproduction and Adaptation
• Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours
• Many prokaryotes form metabolically inactive endospores, which can remain viable in harsh conditions for centuries
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Fig. 27-9
Endospore
0.3 µm
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• Prokaryotes can evolve rapidly because of their short generation times
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Fig. 27-10EXPERIMENT
RESULTS
Daily serial transfer
0.1 mL(population sample)
Old tube(discardedaftertransfer)
New tube(9.9 mLgrowthmedium)
Fit
nes
s re
lati
veto
an
ces
tor
Generation0 5,000 10,000 15,000 20,000
1.0
1.2
1.4
1.6
1.8
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Fig. 27-10a
EXPERIMENT
Daily serial transfer
0.1 mL(population sample)
Old tube(discardedaftertransfer)
New tube(9.9 mLgrowthmedium)
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Fig. 27-10b
RESULTSF
itn
ess
rela
tive
to a
nce
sto
r
Generation0 5,000 10,000 15,000 20,000
1.0
1.2
1.4
1.6
1.8
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• Prokaryotes have considerable genetic variation
• Three factors contribute to this genetic diversity:
– Rapid reproduction
– Mutation
– Genetic recombination
Concept 27.2: Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes
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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 diversity from mutations allows for rapid evolution
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Genetic Recombination
• Additional diversity arises from genetic recombination
• Prokaryotic DNA from different individuals can be brought together by transformation, transduction, and conjugation
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Transformation and Transduction
• A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation
• Transduction is the movement of genes between bacteria by bacteriophages (viruses that infect bacteria)
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Fig. 27-11-1
Donorcell
A+ B+
A+ B+
Phage DNA
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Fig. 27-11-2
A+
Donorcell
A+ B+
A+ B+
Phage DNA
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Fig. 27-11-3
Recipientcell
B–
A+
A–
Recombination
A+
Donorcell
A+ B+
A+ B+
Phage DNA
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Fig. 27-11-4
Recombinant cell
Recipientcell
A+ B–
B–
A+
A–
Recombination
A+
Donorcell
A+ B+
A+ B+
Phage DNA
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Conjugation and Plasmids
• Conjugation is the process where genetic material is transferred between bacterial cells
• Sex pili allow cells to connect and pull together for DNA transfer
• A piece of DNA called the F factor is required for the production of sex pili
• The F factor can exist as a separate plasmid or as DNA within the bacterial chromosome
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Fig. 27-12
Sex pilus 1 µm
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The F Factor as a Plasmid
• Cells containing the F plasmid function as DNA donors during conjugation
• Cells without the F factor function as DNA recipients during conjugation
• The F factor is transferable during conjugation
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Fig. 27-13
F plasmid
F+ cell
F– cell
Matingbridge
Bacterial chromosome
Bacterialchromosome
(a) Conjugation and transfer of an F plasmid
F+ cell
F+ cell
F– cell
(b) Conjugation and transfer of part of an Hfr bacterial chromosome
F factor
Hfr cell A+A+
A+
A+
A+A– A– A–
A– A+
RecombinantF– bacterium
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Fig. 27-13-1
F plasmid
F+ cell
F– cell
Matingbridge
Bacterial chromosome
Bacterialchromosome
(a) Conjugation and transfer of an F plasmid
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Fig. 27-13-2
F plasmid
F+ cell
F– cell
Matingbridge
Bacterial chromosome
Bacterialchromosome
(a) Conjugation and transfer of an F plasmid
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Fig. 27-13-3
F plasmid
F+ cell
F– cell
Matingbridge
Bacterial chromosome
Bacterialchromosome
(a) Conjugation and transfer of an F plasmid
F+ cell
F+ cell
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The F Factor in the Chromosome
• 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
• It is assumed that horizontal gene transfer is also important in archaea
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Fig. 27-13-4
F factor
Hfr cell
(b) Conjugation and transfer of part of an Hfr bacterial chromosome
A+
A–
F– cell
A+
A+
A–
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Fig. 27-13-5
F factor
Hfr cell
(b) Conjugation and transfer of part of an Hfr bacterial chromosome
A+
A–
F– cell
A+
A+
A–
A+
A+ A–
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Fig. 27-13-6
F factor
Hfr cell
(b) Conjugation and transfer of part of an Hfr bacterial chromosome
A+
A–
F– cell
A+
A+
A–
A+
A+ A–
RecombinantF– bacterium
A– A+
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R Plasmids and Antibiotic Resistance
• R plasmids carry genes for antibiotic resistance
• Antibiotics select for bacteria with genes that are resistant to the antibiotics
• Antibiotic resistant strains of bacteria are becoming more common
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Concept 27.3: Diverse nutritional and metabolic adaptations have evolved in prokaryotes
• Phototrophs obtain energy from light
• Chemotrophs obtain energy from chemicals
• Autotrophs require CO2 as a carbon source
• Heterotrophs require an organic nutrient to make organic compounds
• These factors can be combined to give the four major modes of nutrition: photoautotrophy, chemoautotrophy, photoheterotrophy, and chemoheterotrophy
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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
– Facultative anaerobes can survive with or without O2
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Nitrogen Metabolism
• Prokaryotes can metabolize nitrogen in a variety of ways
• In nitrogen fixation, some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3)
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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 called heterocytes exchange metabolic products
Video: Cyanobacteria (Video: Cyanobacteria (OscillatoriaOscillatoria))
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Fig. 27-14
Photosyntheticcells
Heterocyte
20 µm
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• In some prokaryotic species, metabolic cooperation occurs in surface-coating colonies called biofilms
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Concept 27.4: 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
• It allows systematists to identify major new clades
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Fig. 27-16
UNIVERSALANCESTOR
Eukaryotes
Korarcheotes
Euryarchaeotes
Crenarchaeotes
Nanoarchaeotes
Proteobacteria
Chlamydias
Spirochetes
Cyanobacteria
Gram-positivebacteria
Do
main
Eu
karyaD
om
ain A
rchaea
Do
main
Bacteria
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• The use of polymerase chain reaction (PCR) has allowed for more rapid sequencing of prokaryote genomes
• A handful of soil many contain 10,000 prokaryotic species
• Horizontal gene transfer between prokaryotes obscures the root of the tree of life
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Archaea
• Archaea share certain traits with bacteria and other traits with eukaryotes
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Fig. 27-UN1
Eukarya
Archaea
Bacteria
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• Some archaea live in extreme environments and are called extremophiles
• Extreme halophiles live in highly saline environments
• Extreme thermophiles thrive in very hot environments
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• Methanogens live in swamps and marshes and produce methane as a waste product
• Methanogens are strict anaerobes and are poisoned by O2
• In recent years, genetic prospecting has revealed many new groups of archaea
• Some of these may offer clues to the early evolution of life on Earth
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Bacteria
• Bacteria include the vast majority of prokaryotes of which most people are aware
• Diverse nutritional types are scattered among the major groups of bacteria
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Fig. 27-UN2
Eukarya
Archaea
Bacteria
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Proteobacteria
• These gram-negative bacteria include photoautotrophs, chemoautotrophs, and heterotrophs
• Some are anaerobic, and others aerobic
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Fig. 27-18a
Alpha
Beta
Gamma
Delta
Epsilon
Proteobacteria
Subgroup: Beta Proteobacteria
Nitrosomonas (colorized TEM)
1 µ
m
Subgroup: Delta Proteobacteria
10 µ
m
Fruiting bodies ofChondromyces crocatus, amyxobacterium (SEM)
Bdellovibrio bacteriophorusattacking a larger bacterium(colorized TEM)
5 µ
m
Helicobacter pylori (colorized TEM)
2 µ
m0.
5 µ
m
Subgroup: Epsilon Proteobacteria
B. bacteriophorus
Thiomargarita namibiensiscontaining sulfur wastes (LM)
Subgroup: Gamma Proteobacteria
Subgroup: Alpha Proteobacteria
Rhizobium (arrows) inside aroot cell of a legume (TEM)
2.5
µm
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Fig. 27-18b
Alpha
Beta
Gamma
Delta
Epsilon
Proteobacteria
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Subgroup: Alpha Proteobacteria
• Many species are closely associated with eukaryotic hosts
• Scientists hypothesize that mitochondria evolved from aerobic alpha proteobacteria through endosymbiosis
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• Example: Rhizobium, which forms root nodules in legumes and fixes atmospheric N2
• Example: Agrobacterium, which produces tumors in plants and is used in genetic engineering
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Fig. 27-18c
Rhizobium (arrows) inside a rootcell of a legume (TEM)
2.5
µm
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Subgroup: Beta Proteobacteria
• Example: the soil bacterium Nitrosomonas, which converts NH4
+ to NO2–
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Fig. 27-18d
Nitrosomonas (colorized TEM)
1 µ
m
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Subgroup: Gamma Proteobacteria
• Examples include sulfur bacteria such as Chromatium and pathogens such as Legionella, Salmonella, and Vibrio cholerae
• Escherichia coli resides in the intestines of many mammals and is not normally pathogenic
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Fig. 27-18e
Thiomargarita namibiensiscontaining sulfur wastes (LM)
0.5
µm
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Subgroup: Delta Proteobacteria
• Example: the slime-secreting myxobacteria
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Fig. 27-18f
Fruiting bodies ofChondromyces crocatus, amyxobacterium (SEM)
10 µ
m
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Fig. 27-18g
Bdellovibrio bacteriophorusattacking a larger bacterium(colorized TEM)
5 µ
m
B. bacteriophorus
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Subgroup: Epsilon Proteobacteria
• This group contains many pathogens including Campylobacter, which causes blood poisoning, and Helicobacter pylori, which causes stomach ulcers
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Fig. 27-18h
Helicobacter pylori (colorized TEM)
2 µ
m
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Chlamydias
• These bacteria are parasites that live within animal cells
• Chlamydia trachomatis causes blindness and nongonococcal urethritis by sexual transmission
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Fig. 27-18i
CHLAMYDIAS
2.5
µm
CYANOBACTERIA
SPIROCHETES
GRAM-POSITIVE BACTERIA
Chlamydia (arrows) inside ananimal cell (colorized TEM)
Leptospira, a spirochete(colorized TEM)
5 µ
m
50
µm
Two species of Oscillatoria,filamentous cyanobacteria (LM)
Streptomyces, the source ofmany antibiotics (colorized SEM)
5 µ
m
1 µ
m
Hundreds of mycoplasmascovering a human fibroblastcell (colorized SEM)
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Fig. 27-18j
2.5
µm
Chlamydia (arrows) inside ananimal cell (colorized TEM)
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Spirochetes
• These bacteria are helical heterotrophs
• Some, such as Treponema pallidum, which causes syphilis, and Borrelia burgdorferi, which causes Lyme disease, are parasites
Page 94
Fig. 27-18k
Leptospira, a spirochete(colorized TEM)
5 µ
m
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Cyanobacteria
• These are photoautotrophs that generate O2
• Plant chloroplasts likely evolved from cyanobacteria by the process of endosymbiosis
Page 96
Fig. 27-18l
50 µ
m
Two species of Oscillatoria,filamentous cyanobacteria (LM)
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Gram-Positive Bacteria
• Gram-positive bacteria include
– Actinomycetes, which decompose soil
– Bacillus anthracis, the cause of anthrax
– Clostridium botulinum, the cause of botulism
– Some Staphylococcus and Streptococcus, which can be pathogenic
– Mycoplasms, the smallest known cells
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Fig. 27-18m
Streptomyces, the source of manyantibiotics (colorized SEM)
5 µ
m
Page 99
Fig. 27-18n
1 µ
m
Hundreds of mycoplasmascovering a human fibroblastcell (colorized SEM)
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Concept 27.5: 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 Cycling
• Prokaryotes play a major role in the recycling of chemical elements between the living and nonliving components of 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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• Prokaryotes can sometimes increase the availability of nitrogen, phosphorus, and potassium for plant growth
• Prokaryotes can also “immobilize” or decrease the availability of nutrients
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Fig. 27-19
Nobacteria
Strain 1 Strain 2 Strain 3
Soil treatment
Up
take
of
K b
y p
lan
ts (
mg
)
0
0.2
0.4
0.6
0.8
1.0
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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
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• In mutualism, both symbiotic 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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Concept 27.6: Prokaryotes have both harmful and beneficial impacts on humans
• Some prokaryotes are human pathogens, but 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
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Fig. 27-21a
Deer tick
Page 111
5 µm
Fig. 27-21b
Borrelia burgdorferi (SEM)
5 µm
Page 112
Fig. 27-21c
Lyme disease rash
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• Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins
• Exotoxins 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
• 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 the principal agents in bioremediation, the use of organisms to remove pollutants from the environment
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• Some other uses of prokaryotes:
– Recovery of metals from ores
– Synthesis of vitamins
– Production of antibiotics, hormones, and other products
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Fig. 27-22
(a)
(b)
(c)
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Fig. 27-UN3
Fimbriae
Capsule
Cell wall
Circular chromosome
Internalorganization
Flagella
Sex pilus
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You should now be able to:
1. Distinguish between the cell walls of gram-positive and gram-negative bacteria
2. State the function of the following features: capsule, fimbriae, sex pilus, nucleoid, plasmid, and endospore
3. Explain how R plasmids confer antibiotic resistance on bacteria
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4. Distinguish among the following sets of terms: photoautotrophs, chemoautotrophs, photoheterotrophs, and chemoheterotrophs; obligate aerobe, facultative anaerobe, and obligate anaerobe; mutualism, commensalism, and parasitism; exotoxins and endotoxins