Chapter 22
Bacteria: The
Proteobacteria
1
The phylum Proteobacteria
• The largest phylogenetically
coherent bacterial group with over
2,000 species assigned to more than
500 genera
2
Phylogenetic Relationships Among
the Procaryotes
Figure 22.1
3
Phylogenetic Relationships Among Major
Groups Within the a-Proteobacteria
Figure 22.2
4
The Purple Nonsulfur Bacteria
5
Purple nonsulfur bacteria…
• Metabolically flexible
– normally grow anaerobically as anoxygenic
photoorganoheterotrophs
• possess bacteriochlorophylls a or b in
• some can use low levels of H2S as electron
source
– in absence of light, most grow aerobically as
chemoorganoheterotrophs
– in absence of light, some carry out
fermentations and grow anaerobically
6
Purple nonsulfur bacteria…
• Found in mud and water of lakes and ponds
with abundant organic matter and low sulfide
levels; some marine species
• Many genera can produce cellular cysts
– resting cells
– resistant to desiccation but less tolerant of
heat and UV than bacterial endspores
– made in response to nutrient limitation
– have thick outer coat and store
polyhydroxybutyrate
7
Figure 22.3
8
Rickettsia and Coxiella
• Genus Rickettsia
– class Alphaproteobacteria; order
Rickettsiales; family Rickettsiaceae
• Genus Coxiella
– class Gammaproteobacteria; order
Legionellales; family Coxiellaceae
These are considered together because of
important similarities
9
Common features
• Rod-shaped, coccoid, or pleomorphic
– typical gram-negative cell walls
– no flagella
– very small
• Rickettsia – 0.3 to 0.5 by 0.8 to 2.0 m
• Coxiella – 0.2 to 0.4 by 0.4 to 1.0 m
• Parasitic or mutualistic
– parasitic species grow in vertebrate
erythrocytes, macrophages, and vascular
endothelial cells
• also live in blood-sucking arthropods, which
serve as vectors or primary hosts
10
Parasitic life styles
Rickettsia
enters host by
phagocytosis

escapes phagosome

reproduces in
cytoplasm

host cell bursts
11
Coxiella
enters host by
phagocytosis

remains in phagosome

reproduces in
phagolysosome

host cell bursts
human
fibroblast
filled with
Rickettsia
prowazekii
Figure 22.4 (a)
12
Coxiella
burnetti
growing
within
fibroblast
vacuole
Figure 22.4 (c)
13
Rickettsia metabolism
• Lack glycolytic pathway
– do not use glucose as energy source
• Oxidize glutamate and TCA cycle
intermediates (e.g., succinate)
• Take up and use ATP and other
materials from host cell
14
Important pathogens
• Rickettsia prowazekii and Rickettsia
typhi – typhus fever
• Rickettsia rickettsii – Rocky
Mountain Spotted Fever
• Coxiella burnetti – Q fever
• many are important pathogens in
dogs, horses, sheep, and cattle
15
Genus Rhizobium
• Gram-negative, motile rods
– often contain poly-b-hydroxybutyrate
granules
– become pleomorphic under adverse
conditions
• Grow symbiotically as nitrogenfixing bacteroids within root nodule
cells of legumes
16
Figure 22.9
17
Genus Agrobacterium
• Do not stimulate nodule formation or fix
nitrogen
• Invade crown, roots, and stems of many
plants
– transform infected plant cells into
autonomously proliferating tumors
• e.g., Agrobacterium tumefaciens
– causes crown gall disease by means of
tumor-inducing (Ti) plasmid
18
Figure 22.10
19
Nitrifying Bacteria
• Divided into several taxa
– class Alphaproteobacteria; family
Bradyrhizobiaceae – e.g., genus Nitrobacter
– class Betaproteobacteria; family
Nitrosomonadaceae – e.g., genera
Nitrosomonas and Nitrosospira
– class Gammaproteobacteria
• family Ectothiorhodospiraceae – e.g., genus
Nitrococcus
• family Chromatiaceae – e.g., genus Nitrosococcus
20
Table 22.2
21
Figure 22.11
22
Nitrification
• ammonianitritenitrate
• conversion of ammonia to nitrate by
action of two genera
– e.g., Nitrosomonas – ammonia to nitrite
– e.g., Nitrobacter – nitrite to nitrate
• Fate of nitrate
– easily used by plants
– lost from soil through leaching or
denitrification
23
Phylogenetic Relationships Among Major
Groups Within the b-Proteobacteria
Figure 22.12
24
Table 22.3
25
Order Neisseriales
26
Genus Neisseria
• Inhabitants of mucous membranes of
mammals
– some human pathogens
• Neisseria gonorrhoeae – gonorrhea
• Neisseria meningitidis - meningitis
27
Order Burkholderiales
• Contains four families, three with
well-known genera
– genus Burkholderia in family
Burkholderiaceae
– genus Bordetella in family
Alcaliginaceae
– genera Sphaerotilus and Leptothrix in
family Comamonadaceae
28
Genus Burkholderia
• Gram-negative, non–spore-forming,
straight rods
– most motile with single flagellum or tuft of
polar flagella
• aerobic and mesophilic
• nonfermentative chemoorganotrophs
– catalase positive; often oxidase positive
– most use poly-b-hydroxybutyrate as carbon
reserve
29
e.g., Burkholderia cepacia
• degrades > 100 organic molecules
– very active in recycling organic
material
• plant pathogen
• has become a major nosocomial
pathogen
– particular problem for cystic fibrosis
patients
30
Nitrogen Fixation by Burkholderia
and Ralstonia
• Both genera form symbiotic
associations with legumes similar to
that formed by rhizobia
• Both genera have nodulation genes
(nod) similar to rhizobia suggesting a
common genetic origin
– genetic information may have been
obtained through lateral gene transfer
31
Order Nitrosomonadales
• Contains a number of
chemolithotrophs
– two genera of nitrifying bacteria
• Nitrosomonas and Nitrosospira
– genus Gallionella
• stalked bacterium
– genus Spirillum (in family Spirillaceae)
32
Figure 22.15
33
Order Hydrogenophilales
• contains genus Thiobacillus
– well studied chemolithotroph
– prominent member of colorless sulfur
bacteria
• chemolithotrophs that oxidize sulfur
compounds
• other colorless sulfur bacteria are in class
Gamma proteobacteria
34
Genus Thiobacillus
• found in soil and aquatic habitats
– production of sulfuric acid can cause corrosion of
concrete and metal structures
– may increase soil fertility by releasing sulfate
– used in leaching metals from low grade metal ores
35
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Figure 22.16
36
Phylogenetic Relationships Among
g-Proteobacteria
• largest
subgroup of
proteobacteria
• contains 14
orders, and 25
families
Figure 22.17 (a)
37
Figure 22.17 (b)
38
The Purple Sulfur Bacteria
• placed in order Chromatiales
– divided into two families,
Chromatiaceae and
Ectothiorhodospiraceae
– Family Ectothiorhodospiraceae
contains eight genera
39
Figure 22.18
40
Family Chromatiaceae
• typical purple sulfur bacteria
• strict anaerobes
• usually photoautolithotrophs
– use H2S as electron donor
• deposit sulfur granules internally
• often eventually oxidize sulfur to sulfate
– may also use hydrogen as electron donor
• usually found in anaerobic, sulfide-rich zones
of lakes
– can cause large blooms in bogs and lagoons
• e.g., genera Thiospirillum, Thiocapsa, and
Chromatium
41
Figure 22.19
42
Figure 22.20 (a)
43
Order Methylococcales
• contains family Methylococcaceae; seven genera
• morphologically diverse
– e.g., genus Methylococcus – spherical, nonmotile
– e.g., genus Methylomonas – straight, curved, or
branched rods with single polar flagella
– almost all form resting stage (cystlike structure)
• methylotrophs
– use reduced one-carbon compounds as sole carbon
and energy source
44
Methane oxidation
• occurs in complex arrays of
intracellular membranes
• oxidized to methanol and then to
formaldehyde
– electrons donated to electron transport
chain for ATP synthesis
– formaldehyde can be assimilated into
cell material
45
Order Pseudomonadales
• contains family Pseudomonadaceae; 15
genera
– Pseudomonas is the most important genus
in the order Pseudomonadales
• gram-negative straight or slightly curved rods
• 0.5 to 1.0 m by 1.5 to 5.0 m in length
• motile by one or several polar flagella
• lack prosthecae or sheaths
46
Pseudomonas
• chemoheterotrophs with respiratory
metabolism
– usually use oxygen as electron acceptor
– sometimes use nitrate as electron
acceptor
– have functional TCA cycle
– most hexoses are degraded by EntnerDoudoroff pathway
47
Practical importance of
pseudomonads
• metabolically versatile
– degrade wide variety of organic molecules
– mineralization
• microbial breakdown of organic materials to
inorganic substrates
• important experimental subjects
• some are major animal and plant
pathogens
• some cause spoilage of refrigerated food
– can grow at 4°C
48
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Figure 22.24
49
Figure 22.25
50
Order Enterobacteriales
• contains one family,
Enterobacteriaceae; over 44 genera
– referred to as enterobacteria or enteric
bacteria (enterobacteria)
• facultative anaerobes
• chemoorganotrophs that degrade
sugars by glycolytic pathway
– can cleave pyruvate to yield formic
acid (formic acid fermentation)
51
Figure 22.29
52
Table 22.7
53
Table 22.7 (continued)
54
Escherichia coli
• Probably best studied bacterium
• inhabitant of intestinal tracts of many
animals
• Used as indicator organisms for testing
water for fecal contamination
• Some strains are pathogenic
– gastroenteritis
– urinary tract infections
55
Important pathogenic enteric
bacteria
• Salmonella – typhoid fever and
gastroenteritis
• Shigella – bacillary dysentery
• Klebsiella – pneumonia
• Yersinia - plague
• Erwinia – blights, wilts, etc., of crop
plants
56
Figure 22.30
57
Order Pasteurellales
• contains one family, Pasteurellaceae;
six genera
58
Important pathogens
• Pasteurella multiocida – fowl cholera
• Pasteurella haemolytica – pneumonia
in cattle, sheep and goats
• Haemophilus influenzae – variety of
diseases, including meningitis in
children
59
Class Deltaproteobacteria
• contains eight orders and 20 families
– divided into two general groups
• aerobic, chemoorganotrophic predators
• anaerobic, chemoorganotrophic sulfurand sulfate-reducers
60
Figure 22.31
61
62
Orders Desulfovibrionales,
Desulfobacterales, and
Desulfuromonadales
• Strict anaerobes
• Sulfur- or sulfate-reducing bacteria
– use sulfur and sulfate as electron acceptors during
anaerobic respiration
– electron transport chain used to generate ATP
• Widespread in muds and sediments of aquatic
environments, including sewage treatment
systems
– important in sulfur cycling
63
Figure 22.32
64
Order Bdellovibrionales
– best studied is Bdellovibrio
• predatory bacteria
65
Bdellovibrio
bactivorus
Figure 22.23
66
Figure 22.34 (a)
67
Epsilon Proteobacteria
• Smallest of proteobacterial classes
• Consists of one order,
Campylobacteriales; three families
68
Figure 22.38
69
Genus Campylobacter
• Contains both pathogenic and
nonpathogenic species
– Campylobacter fetus
• reproductive disease and abortions in cattle and
sheep
• septicemia and enteritis in humans
– septicemia – pathogens or their toxins in blood
– enteritis – inflammation of intestinal tract
– Campylobacter jejuni
• abortions in sheep
• enteritis diarrhea in humans
70
Genus Helicobacter
• At least 14 species isolated from stomachs
and upper intestines of humans, dogs,
cats, and other mammals
• e.g., Helicobacter pylori
– causes gastritis and peptic ulcer disease
– produces large quantities of urease
• urea hydrolysis appears to be associated with
virulence
71