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CHAPTER
11
The
Prokaryotes:
Domains
Bacteria and
Archaea
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Table 11.1 Classification of Selected Prokaryotes*
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Gram-Negative Bacteria
Learning Objectives
11-1 Differentiate the alphaproteobacteria described in this
chapter by drawing a dichotomous key.
11-2 Differentiate the betaproteobacteria described in this
chapter by drawing a dichotomous key.
11-3 Differentiate the gammaproteobacteria described in
this chapter by drawing a dichotomous key.
11-4 Differentiate the deltaproteobacteria described in this
chapter by drawing a dichotomous key.
11-5 Differentiate the epsilonproteobacteria described in
this chapter by drawing a dichotomous key.
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Proteobacteria
• From the mythological Greek god Proteus, who
could assume many shapes
• Gram-negative
• Chemoheterotrophic
• Largest taxonomic group of bacteria
• Five classes
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The Alphaproteobacteria
• Most are capable of growing with very low levels
of nutrients
• Many have stalks or buds known as prosthecae
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The Alphaproteobacteria
• Pelagibacter
•
•
•
•
One of the most abundant microorganisms in oceans
Extremely small
Advantage in low-nutrient environments
Important role in Earth's carbon cycle
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The Alphaproteobacteria
• Azospirillum
• Grows in soil, using nutrients excreted by plants
• Forms associations with roots
• Fixes nitrogen
• Acetobacter and Gluconobacter
• Convert ethanol into acetic acid
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The Alphaproteobacteria
• Rickettsia
• Obligate intracellular parasites
• Cause spotted fevers
• R. prowazekii: epidemic typhus
• R. typhi: endemic murine typhus
• R. rickettsii: Rocky Mountain spotted fever
• Transmitted by insect and tick bites
• Ehrlichia
• Transmitted by ticks
• Cause ehrlichiosis
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Figure 11.1 Rickettsias.
Slime
layer
Scattered
rickettsias
Chicken
embryo
cell
Nucleus
Masses of
rickettsias in
nucleus
A rickettsial cell
that has just been
released from a host
cell
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Rickettsias grow
only within a host cell,
such as the chicken
embryo cell shown
here. Note the
scattered rickettsias
within the cell and the
compact masses of
rickettsias in the cell
nucleus.
The Alphaproteobacteria
• Caulobacter and Hyphomicrobium
• Found in low-nutrient aquatic environments
• Form stalks and prosthecae
• Reproduce via budding rather than binary fission
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Figure 11.2 Caulobacter.
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Figure 11.3 Hyphomicrobium, a type of budding bacterium.
Hypha
Holes in
filter
Bud
Bud
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The Alphaproteobacteria
• Rhizobium and Bradyrhizobium
• Fix nitrogen in the roots of leguminous plants
• Known by the common name of rhizobia
• Agrobacterium
• Plant pathogen; causes crown gall
• Inserts a plasmid into plant cells, inducing a tumor
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Figure 9.19 Crown gall disease on a rose plant.
Crown gall
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The Alphaproteobacteria
• Bartonella
• Human pathogen
• B. henselae: cat-scratch disease
• Brucella
• Obligate parasite of mammals; survives phagocytosis
• Causes brucellosis
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The Alphaproteobacteria
• Nitrobacter and Nitrosomonas
• Chemoautotrophic; use inorganic chemicals as energy
source; CO2 as carbon source
• Nitrosomonas: NH4+ → NO2–
• Nitrobacter: NO2– → NO3–
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The Alphaproteobacteria
• Wolbachia
• Endosymbiont of insects
• Affects reproduction of insects
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Applications of Microbiology 11.1a
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Applications of Microbiology 11.1b
Males
Females
Neither infected
Uninfected offspring
Male infected
No offspring
Female infected
Infected offspring
Both infected
Infected offspring
Wolbachia
Unfertilized female infected
Infected female offspring
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Check Your Understanding
 Make a dichotomous key to distinguish the
alphaproteobacteria described in this chapter.
(Hint: See page 292 for a completed example.
11-1
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The Betaproteobacteria
• Acidithiobacillus
• Chemoautotrophic; oxidize sulfur to sulfates:
H2S → SO42–
• Spirillum
• Found in freshwater
• Move via flagella
• Sphaerotilus
• Found in freshwater and sewage
• Form sheaths to aid in protection and nutrient gathering
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Figure 11.4 Spirillum volutans.
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Figure 11.5 Sphaerotilus natans.
Bacterial
cells
Sheath
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The Betaproteobacteria
• Burkholderia
• B. cepacia: degrades more than 100 organic molecules
• B. pseudomallei: causes meliodosis
• Bordetella
• Non-motile rods
• B. pertussis: causes whooping cough
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The Betaproteobacteria
• Neisseria
• N. gonorrhoeae: cause of gonorrhoea
• N. meningitidis: cause of meningococcal meningitis
• Zoogloea
• Important in the activity of the activated sludge system
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Figure 11.6 The gram-negative coccus Neisseria gonorrhoeae.
Bacteria
Host-cell
membrane
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Check Your Understanding
 Make a dichotomous key to distinguish the
betaproteobacteria described in this chapter.
11-2
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The Gammaproteobacteria
• Thiotrichales
• Beggiatoa
• Grows in aquatic sediments
• Chemoautotrophic; oxidize H2S to S0 for energy
• Francisella
• F. tularensis: causes tularemia
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The Gammaproteobacteria
• Pseudomonadales
• Pseudomonas
•
•
•
•
Opportunistic pathogens; nosocomial infections
Metabolically diverse
Polar flagella; common in soil
P. aeruginosa: wound and urinary tract infections
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Figure 11.7 Pseudomonas.
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The Gammaproteobacteria
• Pseudomonadales (cont'd)
• Azotobacter and Azomonas
• Nitrogen-fixing
• Moraxella
• M. lacunata: causes conjunctivitis
• Acinetobacter
• A. baumanii: respiratory pathogen; resistant to antibiotics
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The Gammaproteobacteria
• Legionellales
• Legionella
• Found in streams, warm-water pipes, and cooling towers
• Causes legionellosis
• Coxiella
• C. burnetii: causes Q fever; transmitted via aerosols or
milk
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Figure 24.13b Coxiella burnetii, the cause of Q fever.
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The Gammaproteobacteria
• Vibrionales
• Found in aquatic habitats
• V. cholerae causes cholera
• V. parahaemolyticus causes gastroenteritis
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Figure 11.8 Vibrio cholerae.
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The Gammaproteobacteria
• Enterobacteriales
• Commonly called enterics — inhabit the intestinal tract;
ferment carbohydrates
• Facultative anaerobes
• Peritrichous flagella
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The Gammaproteobacteria
• Enterobacteriales (cont'd)
• Escherichia
• E. coli: indicator of fecal contamination; causes foodborne
disease and urinary tract infections
• Salmonella
• 2400 serovars
• Common form of foodborne illness
• Salmonella typhi causes typhoid fever
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The Gammaproteobacteria
• Enterobacteriales (cont'd)
• Shigella
• Causes bacillary dysentery
• Klebsiella
• K. pneumoniae causes pneumonia
• Serratia
• Produces red pigment
• Common cause of nosocomial infections
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The Gammaproteobacteria
• Enterobacteriales (cont'd)
• Proteus
• Swarming motility; colonies form concentric rings
• Yersinia
• Y. pestis causes plague
• Transmitted via fleas
• Erwinia
• Plant pathogens
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Figure 11.9 Proteus mirabilis.
Flagella
Proteus mirabilis with peritrichous
flagella
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A swarming colony of Proteus
mirabilis, showing concentric rings
of growth
The Gammaproteobacteria
• Enterobacteriales (cont'd)
• Enterobacter
• E. cloacae and E. aerogenes cause urinary tract
infections and nosocomial infections
• Cronobacter
• Discovered in 2007
• C. sakazakii causes meningitis; found in a variety of
environments and foods
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The Gammaproteobacteria
• Pasteurellales
• Pasteurella
• Pathogen of domestic animals
• P. multocida is transmitted to humans via animal bites
• Haemophilus
• Require X factor (heme) and V factor (NAD+, NADP+) in
media
• H. influenzae causes meningitis, earaches, and epiglottitis
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Check Your Understanding
 Make a dichotomous key to distinguish the orders
of gammaproteobacteria described in this chapter.
11-3
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The Deltaproteobacteria
• Bdellovibrio
• Attacks other gram-negative bacteria
• Desulfovibrionales
• Use S0 or SO42– instead of O2 as final electron
acceptors
• Desulfovibrio is found in anaerobic sediments and
intestinal tracts
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Figure 11.10 Bdellovibrio bacteriovorus.
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The Deltaproteobacteria
• Myxococcales
• Myxo = mucus
• Move by gliding and leave a slime trail
• Cells aggregate and form a fruiting body containing
myxospores
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Figure 11.11 Myxococcales.
Myxobacteria fruiting body
Myxospores
Myxospores are resistant
resting cells released from
sporangioles upon
favorable conditions.
Sporangiole
Mounds of myxobacteria
differentiate into a mature
fruiting body, which
produces myxospores
packed within
sporangioles.
Mounding
Aggregations of
cells heap up into a
mound, an early
fruiting body.
Myxospores
Germination
Myxospores germinate and
form gram-negative
vegetative cells, which
divide to reproduce.
Vegetative growth cycle
Vegetative myxobacteria
are motile by gliding,
forming visible slime trails.
Aggregation
Under favorable conditions, the
vegetative cells swarm to central
locations, forming an aggregation.
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Check Your Understanding
 Make a dichotomous key to distinguish the
deltaproteobacteria described in this chapter.
11-4
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The Epsilonproteobacteria
• Helical or curved; microaerophilic
• Campylobacter
• One polar flagellum
• C. jejuni causes foodborne intestinal disease
• Helicobacter
• Multiple flagella
• Cause peptic ulcers and stomach cancer
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Figure 11.12 Helicobacter pylori.
Flagella
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Check Your Understanding
 Make a dichotomous key to distinguish the
epsilonproteobacteria described in this chapter.
11-5
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The Nonproteobacteria Gram-Negative Bacteria
Learning Objective
11-6 Differentiate planctomycetes, chlamydias,
Bacteroidetes, Cytophaga, and Fusobacteria
by drawing a dichotomous key.
11-7 Compare and contrast purple and green
photosynthetic bacteria with the cyanobacteria.
11-8 Describe the features of spirochetes and
Deinococcus.
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Cyanobacteria (The Oxygenic Photosynthetic
Bacteria)
• Carry out oxygenic photosynthesis
• Many contain heterocysts that can fix nitrogen
• Gas vesicles that provide buoyancy
• Unicellular or filamentous
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Figure 11.13 Cyanobacteria.
Heterocysts
Glycocalyx
Filamentous cyanobacterium
showing heterocysts, in which
nitrogen-fixing activity is located
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A unicellular, nonfilamentous
cyanobacterium, Gloeocapsa. Groups
of these cells, which divide by binary
fission, are held together by the
surrounding glycocalyx.
The Phyla Chlorobi and Chloroflexi (The
Anoxygenic Photosynthetic Bacteria)
• Carry out anoxygenic photosynthesis
• Green sulfur: phylum Chlorobi
• Green nonsulfur: phylum Chloroflexi
• Purple sulfur and purple nonsulfur photosynthetic
bacteria are proteobacteria
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Figure 11.14 Purple sulfur bacteria.
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Table 11.2 Selected Characteristics of Photosynthesizing Bacteria
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Chlamydiae
• No peptidoglycan in the cell wall; grow
intracellularly
• Chlamydia and Chlamydophila
• Form an elementary body that is infective
• Chlamydia trachomatis causes trachoma and urethritis
• Chlamydophila psittaci causes respiratory psittacosis
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Figure 11.15a Chlamydias.
Elementary body
The elementary bodies
are released from the
host cell.
The bacterium's infectious
form, the elementary
body, attaches to a host
cell.
Nucleus
The reticulate bodies
begin to convert back to
elementary bodies.
Host cell
The host cell phagocytizes
the elementary body,
housing it in a vacuole.
Vacuole forming
Vacuole
Reticulate body
The reticulate body divides
successively, producing
multiple reticulate bodies.
Life cycle of the chlamydias, which takes about 48 hours to complete
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The elementary body
reorganizes to form a
reticulate body.
Figure 11.15b Chlamydias.
Elementary body
Reticulate body
Intermediate body
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Micrograph of Chlamydophila psittaci in the cytoplasm of a
host cell. The elementary bodies are the infectious stage; they
are dense, dark, and relatively small. Reticulate bodies, the
form in which chlamydias reproduce within the host cell, are
larger with a speckled appearance. Intermediate bodies, a stage
between the two, have a dark center.
Planctomycetes
• Gemmata obscuriglobus has a membrane around
DNA resembling a eukaryotic nucleus
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Figure 11.16 Gemmata obscuriglobus.
Nucleoid
Nuclear
envelope
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The Nonproteobacteria Gram-Negative Bacteria
• Bacteroidetes
• Anaerobic
• Bacteroides are found in the mouth and large intestine
• Cytophaga degrade cellulose in soil
• Fusobacteria
• Anaerobic
• Are found in the mouth; cause dental abscesses
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Figure 11.17 Fusobacterium.
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Spirochaetes
• Coiled and move via axial filaments
• Treponema
• T. pallidum causes syphilis
• Borrelia
• Causes relapsing fever and Lyme disease
• Leptospira
• Excreted in animal urine
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Figure 11.18 Spirochetes.
Axial
filaments
Sheath
This cross section of a spirochete
shows numerous axial filaments between
the dark cell and the outer sheath.
Axial filament
anchored at one
end to cell body
Sheath
Body of cell
Axial filament
The end of an axial filament (endoflagellum) is attached to the cell and extends
through most of the length of the cell. Another axial filament is attached to the
opposite end of the cell. These axial filaments do not extend away from the cell but
remain between the body of the cell and the external sheath. Their contractions
and relaxations cause the helical cell to rotate in a corkscrew fashion.
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Deinococci
• Deinococcus radiodurans
• More resistant to radiation than endospores
• Thermus aquaticus
• Found in a hot spring in Yellowstone National Park
• Source of Taq polymerase
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Check Your Understanding
 Which gram-negative group has a life cycle that
includes different stages?
11-6
 Both the purple and green photosynthetic bacteria
and the photosynthetic cyanobacteria use plantlike
CO2 fixation to make carbohydrates. In what way
does the photosynthesis carried out by these two
groups differ from plant photosynthesis?
11-7
 The axial filament distinguishes what genera of
bacteria?
11-8
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The Gram-Positive Bacteria
Learning Objective
11-9 Differentiate the genera of firmicutes
described in this chapter by drawing a
dichotomous key.
11-10 Differentiate the actinobacteria described in
this chapter by drawing a dichotomous key.
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The Gram-Positive Bacteria
• Firmicutes (low G + C ratios)
• Actinobacteria (high G + C ratios)
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Firmicutes (Low G + C Gram-Positive Bacteria)
• Clostridiales
• Clostridium
• Endospore-producing
• Obligate anaerobes
• Includes disease-causing C. tetani, C. botulinum, C.
perfringens, and C. difficile
• Epulopiscium
• Can be seen with the unaided eye
• Daughter cells form within the parent cell; no binary
fission
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Figure 11.19 Clostridium difficile.
Endospore
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Figure 11.20 A giant prokaryote, Epulopiscium fishelsoni.
Epulopiscium
Paramecium
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Firmicutes (Low G + C Gram-Positive Bacteria)
• Bacillales
• Bacillus
•
•
•
•
Endospore-producing rods
B. anthracis causes anthrax
B. thuringiensis is an insect pathogen
B. cereus causes food poisoning
• Staphylococcus
• Grapelike clusters
• S. aureus causes wound infections, is often antibiotic
resistant, and produces an enterotoxin
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Figure 11.21 Bacillus.
Endospore
Collapsed
B. thuringiensis
Toxic crystal
Bacillus thuringiensis. The diamond-shaped
crystals shown next to the endospore are toxic
to insects that ingest them. This electron
micrograph was made using the technique of
shadow casting.
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Figure 11.22 Staphylococcus aureus.
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Firmicutes (Low G + C Gram-Positive Bacteria)
• Lactobacillales
• Aerotolerant anaerobes; produce lactic acid from simple
carbohydrates
• Lactobacillus colonize the body and are used
commercially in food production
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Firmicutes (Low G + C Gram-Positive Bacteria)
• Lactobacillales (cont'd)
• Streptococcus
• Spherical in chains
• Produce enzymes that destroy tissue
• Beta-hemolytic streptococci hemolyze blood agar;
includes S. pyogenes
• Non-beta-hemolytic streptococci include S. pneumoniae
and S. mutans, which causes dental caries
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Figure 11.23 Streptococcus.
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Firmicutes (Low G + C Gram-Positive Bacteria)
• Lactobacillales (cont'd)
• Enterococcus
• Found in intestinal tract; hospital contaminants
• E. faecalis and E. faecium infect surgical wounds and the
urinary tract
• Listeria
• L. monocytogenes contaminates food
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Firmicutes (Low G + C Gram-Positive Bacteria)
• Mycoplasmatales
• Lack a cell wall; pleomorphic
• M. pneumoniae causes mild pneumonia
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Figure 11.24 Mycoplasma pneumoniae.
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Check Your Understanding
 To which genus is Enterococcus more closely
related: Staphylococcus or Lactobacillus?
11-9
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Actinobacteria (High G + C Gram-Positive
Bacteria)
• High G + C
• Gram-positive
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Actinobacteria (High G + C Gram-Positive
Bacteria)
• Often pleomorphic; branching filaments
• Often common inhabitants of soil
• Mycobacterium
• Outermost layer of mycolic acids that is waxy and waterresistant
• Often slow-growing
• M. tuberculosis causes tuberculosis
• M. leprae causes leprosy
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Actinobacteria (High G + C Gram-Positive
Bacteria)
• Corynebacterium
• C. diphtheriae causes diphtheria
• Propionibacterium
• Forms propionic acid
• P. acnes causes acne
• Gardnerella
• G. vaginalis causes vaginitis
• Frankia
• Forms N-fixing nodules on tree roots
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Actinobacteria (High G + C Gram-Positive
Bacteria)
• Streptomyces
• Isolated from soil; produce most antibiotics
• Actinomyces
• Form filaments in the mouth and throat; destroy tissue
• Nocardia
• Form fragmenting filaments; acid-fast
• N. asteroides causes pulmonary infections
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Figure 11.25 Streptomyces.
Conidiospores
in coils
Filament
Drawing of a typical streptomycete showing filamentous, branching
growth with asexual reproductive conidiospores at the filament tips
Filament
Conidiospores in coils
Coils of conidiospores supported by filaments of
the streptomycete
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Figure 11.26 Actinomyces.
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Check Your Understanding
 What group of bacteria makes most of the
commercially important antibiotics?
11-10
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Diversity Within the Archaea
Learning Objective
11-11 Name a habitat for each group of archaea.
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Diversity Within the Archaea
• Distinct taxonomic grouping; lack peptidoglycan
• Extremophiles
• Halophiles
• Require salt concentration >25%
• Thermophiles
• Require growth temperature >80 C
• Methanogens
• Anaerobic and produce methane
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Figure 11.27 Archaea.
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Check Your Understanding
 What kind of archaea would populate solar
evaporating ponds?
11-11
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Microbial Diversity
Learning Objective
11-12 List two factors that contribute to the limits of
our knowledge of microbial diversity.
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Microbial Diversity
• Bacteria size range
• Thiomargarita (diameter of 750 µm)
• Carsonella ruddii (182 genes)
• PCR indicates up to 10,000 bacterial species per
gram of soil
• Many bacteria have not been identified
• Have not been cultured
• Are a part of complex food chains requiring the products
of other bacteria
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Figure 11.28 Thiomargarita namibiensis.
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Check Your Understanding
 How can you detect the presence of a bacterium
that cannot be cultured?
11-12
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