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Chapter 11
The Prokaryotes: Domains
Bacteria and Archaea
Part 1
The Prokaryotes:
Domains Bacteria and Archaea
• One circular chromosome (no histones),
not in a membrane (no nucleus)
• No organelles
• 70S ribosomes
• Peptidoglycan cell walls (mainly bacteria)
• Binary fission
Domain Archaea
• Discovered in late 1970s; highly diverse
group
• rRNA sequence differ from Domains
Bacteria & Eukarya
• Cell wall lacks peptidoglycan; a few lack cell
wall
• Some are gram-positive and some are gramnegative
Domain Archaea
• Binary fission,
fragmentation or
budding
• Most are
morphologically
similar to bacteria
(rods, cocci, and
helixes); but some
are very unusual
Disk-shaped Pyrodictium abyssi
Figure 11.25
Domain Archaea
• Physiologically diverse (aerobic, facultative
anaerobe, and strict/obligate anaerobe)
• Chemoautotrophs, photoautotrophs, and
chemoheterotrophs
• Frequent inhabitants of extreme
environments (heat, cold, acidity, and
pressure)
Domain Archaea
• Hyperthermophiles
– Pyrodictium
– Sulfolobus
• Methanogens (economic importance)
– Methanobacterium
derive energy from
combining hydrogen with carbon dioxide to
form methane
• Extreme halophiles
– Halobacterium
– Halococcus
Domain Bacteria
• Proteobacteria
– Mythical Greek god, Proteus, who could assume
many shapes
– Gram-negative; many are chemoheterotrophic
bacteria
– presumed to have arisen from a common
photosynthetic ancestor; few are photosynthetic
today
• The alpha () proteobacteria
– As a group, most are capable of growth at very
low levels of nutrients
The  (alpha) Proteobacteria
• Chemoautotrophs
and chemoheterotrophs
• Include
agriculturally
important
bacteria, and
several plant and
human pathogens
The  (alpha) Proteobacteria
• Some have unusual
morphology
• prosthecae: protrusions
such as stalks or buds
– Caulobacter. Stalked
bacteria found in lakes
– Hyphomicrobium.
Budding bacteria found in
lakes
Figure 11.2 & 3
The  (alpha) Proteobacteria
• Human pathogens:
– Bartonella: several members are human
pathogens
• B. hensela Cat-scratch disease
– Brucella: small nonmotile coccobacilli;
obligate parasites of mammals and cause
diseases brucellosis
The  (alpha) Proteobacteria
• Obligate intracellular parasites: reproduce only
within a mammalian cell
– Ehrlichia: tick-borne, cause ehrlichiosis
– Rickettsia: arthropod-borne (e.g. lice, rat fleas, and
ticks), cause spotted fevers
• R. prowazekii
• R. typhi
• R. rickettsii
Epidemic typhus
Endemic murine typhus
Rocky Mountain Spotted Fever
The  (alpha) Proteobacteria
Figure 11.1
The  (alpha) Proteobacteria
• Wolbachia. Live in
insects and other
animals
– infect over a million
species of insects as
well as spiders,
millipedes, mites,
crustaceans, and
nematodes.
The  (alpha) Proteobacteria
• Plant pathogen:
– Agrobacterium
tumefaciens
• causes a
disease called
crown gall by
inserting a (Ti)
plasmid into
plant cells, &
inducing a
tumor
Figure 9.17
The  (alpha) Proteobacteria
• Agriculturally
important genera
(Nitrogen-fixing &
nitrifying bacteria)
– Azospirillum
• Grow in soil, using
nutrients excreted by
plants
• Fix nitrogen
– Rhizobium
• Fix nitrogen in the
roots of plants
Figure 27.5
The  (alpha) Proteobacteria
– Nitrobacter oxidize nitrogen (ammonium to nitrite)
for energy
– Nitrosomonas oxidize nitrogen (nitrite to nitrate) for
energy
– Both are chemoautotrophic (fix CO2 as C source) .
• Important for the environment and to agriculture
• Industrially important genera
– Acetobacter
– Gluconobacter
Both produce acetic acid
from ethyl alcohol
The  (beta) Proteobacteria
• Considerable overlap between the - and proteobacteria, esp. among the nitrifying
bacteria
• Many use nutrient substances that diffuse
away form areas of anaerobic decomposition
of organic matter
• Chemoautotrophs & chemoheterotrophs
• Include several important pathogenic
bacteria
The  (beta) Proteobacteria
The  (beta) Proteobacteria
• Human pathogens
– Neisseria :
chemoheterotrophic,
cocci
• N. meningitidis
• N. gonorrhoeae
– Bordetella: chemoheterotrophic, rods
• B. pertussis
– Burkholderia: cause
nosocomial infections
Figure 11. 6
The  (beta) Proteobacteria
• Sphaerotilus
– Chemoheterotophic
– form sheaths
– Cause problem in
sewage treatment
• Spirillum
– Chemoheterotrophic
– Helical shaped, but
use flagella (no axial
filaments)
Figures 11.4 & 11.5
The  (beta) Proteobacteria
• Environmentally important genera
– Thiobacillus: Chemoautotrophic, important in
sulfur cycle by oxidizing sulfur (H2S  SO42–)
• Industrially important genera
– Zoogloea: Slimy masses in aerobic sewagetreatment processes
The  (gamma) Proteobacteria
• Largest subgroup of the proteobacteria;
include a great variety of physiological
types
• Many are human and plant pathogens
The  (gamma) Proteobacteria
The  (gamma) Proteobacteria
• Pseudomonadales:
– Pseudomonas
• Opportunistic
pathogens
• Metabolically
diverse
• Polar flagella
– Azotobacter and Azomonas: Nitrogen fixing
– Moraxella: Conjunctivitis
Figure 11.7
The  (gamma) Proteobacteria
• Legionellales:
– Legionella
• Found in streams,
warm-water pipes,
cooling towers
• L. pneumophilia
– Coxiella
• Q fever transmitted
via aerosols or milk
Figure 24.15b
The  (gamma) Proteobacteria
• Vibrionales:
– Found in coastal water
• Vibrio cholerae causes
cholera
• V. parahaemolyticus
causes gastroenteritis
Figure 11.8
The  (gamma) Proteobacteria
• The  (gamma) Proteobacteria
– Enterobacteriales (enterics):
• Peritrichous flagella, facultatively anaerobic
–
–
–
–
–
–
–
–
–
Enterobacter
Erwinia
Escherichia
Klebsiella
Proteus
Salmonella
Serratia
Shigella
Yersinia
The  (gamma) Proteobacteria
Figure 11.9a, b
The  (gamma) Proteobacteria
• Pasteurellales:
– Pasteurella
• Cause pneumonia and septicemia
– Haemophilus
• Require X (heme) and V (NAD+, NADP+) factors
The  (gamma) Proteobacteria
• Beggiatoa
– Chemoautotrophic, oxidize H2S to S0 for
energy
• Francisella
– Chemoheterotrophic, tularemia
Actinobacteria
•
•
•
•
•
•
•
Actinomyces
Corynebacterium
Frankia
Gardnerella
Mycobacterium
Nocardia
Propionibacteriu
m
• Streptomyces
Figure 11.20b
Actinobacteria
•
•
•
•
•
•
•
Actinomyces
Corynebacterium
Frankia
Gardnerella
Mycobacterium
Nocardia
Propionibacteriu
m
• Streptomyces
Figure 11.20b
The  (delta) Proteobacteria
• Include some bacteria that are predators on
other bacteria.
• Contributors to the sulfur cycle
The  (delta) Proteobacteria
– Bdellovibrio: prey on other gram-negative
bacteria
– Desulfovibrionales: sulfur reducing bacteria; use
S instead of O2 as final electron acceptor
• Release millions of tons of H2S into the atmosphere
every year and plays a key part in the sulfur cycle
– Myxococcales: gliding; cells aggregate to form
myxospores; also predatory on other bacteria
The  (delta) Proteobacteria
Figure 11.10a
The  (delta) Proteobacteria
Figure 11.1b
The  (epsilon) Proteobacteria
• Slender gram-negative rods; helical or
vibroids
The  (epsilon) Proteobacteria
• Vibroid: helical bacteria that do not have a
complete turn
• Human pathogens
– Campylobacter: one polar flagellum;
microaerophilic vibrios; cause gastroenteritis
• C. fetus
• C. jejuni
Figure 11.1a
The  (epsilon) Proteobacteria
– Helicobacter:
multiple flagella;
microaerophilic
curbed rods
• H. pylori causes peptic
ulcers & Stomach
cancer
Figure 11.11