1. Bacteria: The Proteobacteria
Chapter 17

2. The Phylogeny of Bacteria
I. Phylum Proteobacteria

3. The Phylogeny of Bacteria – Major phyla of domain Bacteria
Phylogenetic Overview of Bacteria

4. Phylum Proteobacteria
A major lineage (phyla) of Bacteria
Includes many of the most commonly encountered bacteria
Most metabolically diverse of all domain Bacteria
E.g., chemolithotrophy, chemoorganotrophy, phototrophy
Morphologically diverse
Divided into five classes
Alpha-, Beta-, Delta-, Gamma-, Epsilon-

5. Major Genera of Proteobacteria

6. II Phototrophic, Chemolithotrophic & Methanotrophic
Proteobacteria
1. Purple Phototrophic Bacteria
2. The Nitrifying Bacteria
3. Sulfur- and Iron-Oxidizing Bacteria
4. Hydrogen-Oxidizing Bacteria
5. Methanotrophs and Methylotrophs

7. 1. Purple Phototrophic Bacteria
Carry out anoxygenic photosynthesis; no O2 evolved
Morphologically diverse group
Genera fall within the Alpha-, Beta-, or Gammaproteobacteria
Contain bacteriochlorophylls and carotenoid pigments
Produce intracytoplasmic photosynthetic membranes with varying morphologies

8. Liquid Cultures of Phototrophic Purple Bacteria
Figure 15.2

9. Membrane Systems of Phototrophic Purple Bacteria
Figure 15.3

10. Purple Phototrophic Bacteria
Purple Sulfur Bacteria
Use hydrogen sulfide (H2S) as an electron donor for CO2 reduction in photosynthesis
Sulfide oxidized to elemental sulfur (So) that is stored as globules either inside or outside cells
Sulfur later disappears as it is oxidized to sulfate (SO42-)

11. Photomicrographs of Purple Sulfur Bacteria
Figure 15.4

12. Purple Phototrophic Bacteria
Purple Sulfur Bacteria (cont’d)
Many can also use other reduced sulfur compounds, such as thiosulfate (S2O32-)
All are Gammaproteobacteria
Found in illuminated anoxic zones of lakes and other aquatic habitats where H2S accumulates, as well as sulfur springs

13. Genera and Characteristics of Purple Sulfur Bacteria

14. Genera and Characteristics of Purple Sulfur Bacteria

15. Genera and Characteristics of Purple Sulfur Bacteria

16. Blooms of Purple Sulfur Bacteria
Figure 15.5

17. Purple Non-sulfur Bacteria
Originally thought organisms were unable to use sulfide as an electron donor for CO2 reduction, now know most can
Most can grow aerobically in the dark as chemoorganotrophs
Some can also grow anaerobically in the dark using fermentative or anaerobic respiration
Most can grow photoheterotrophically using light as an energy source and organic compounds as a carbon source
All in Alpha- and Betaproteobacteria

18. Representatives of Purple Nonsulfur Bacteria
Figure 15.6

19. Genera and Characteristics of Purple Nonsulfur Bacteria

20. Genera and Characteristics of Purple Nonsulfur Bacteria

21. 2. The Nitrifying Bacteria
Able to grow chemolithotrophically at the expense of reduced inorganic nitrogen compounds
Found in Alpha-, Beta-, Gamma-, and Deltaproteobacteria
Nitrification (oxidation of ammonia to nitrate) occurs as two separate reactions by different groups of bacteria
Ammonia oxidizers (nitrosifyers) (e.g., Nitrosococcus)
Nitrite oxidizer (nitrifyer) (e.g., Nitrobacter)
Many species have internal membrane systems that house key enzymes in nitrification
Ammonia monooxygenase: oxidizes NH3 to NH2OH
Nitrite oxidase: oxidizes NO2- to NO3-

22. Nitrifying Bacteria (cont’d)
Widespread in soil and water
Highest numbers in habitats with large amounts of ammonia
i.e., sites with extensive protein decomposition and sewage treatment facilities
Most are obligate chemolithotrophs and aerobes
One exception is annamox organisms, which oxidize ammonia anaerobically

23. Figure 15.7

24. As carbon dioxide rises, food quality will decline without careful nitrogen management

26. 3. Sulfur- and Iron-Oxidizing Bacteria
Sulfur-Oxidizing Bacteria
Grow chemolithotrophically on reduced sulfur cmpds
Two broad classes
Neutrophiles
Acidophiles (some also use ferrous iron (Fe2+)
Thiobacillus (rods)
Sulfur compounds most commonly used as electron
donors are H2S, So, S2O32-; generates sulfuric acid
Achromatium (spherical cells)
Common in freshwater sediments
Some obligate chemolithotrophs possess special structures that house Calvin cycle enyzmes (carboxysomes)

27. Beggiatoa
Filamentous, gliding bacteria
Found in habitats rich in H2S
e.g., sulfur springs, decaying seaweed beds, mud layers of lakes, sewage polluted waters, and hydrothermal vents
Most grow mixotrophically
with reduced sulfur compounds as electron donors
and organic compounds as carbon sources
Thioploca
Large, filamentous sulfur-oxidizing bacteria that form cell bundles surrounded by a common sheath
Thick mats found on ocean floor off Chile and Peru
Couple anoxic oxidation of H2S with reduction of NO3- to NH4+

28. Non-filamentous Sulfur Chemolithotrophs
Filamentous Sulfur-Oxidizing Bacteria
Figure 15.9

29. Sulfur- and Iron-Oxidizing Bacteria
Sulfur-Oxidizing Bacteria (cont’d)
Thiothrix
Filamentous sulfur-oxidizing bacteria in which filaments group together at their ends by a holdfast to form cellular arrangements called rosettes
Obligate aerobic mixotrophs

30. Thiothrix
Figure 15.12

31. 4. Hydrogen-Oxidizing Bacteria
Most can grow autotrophically with H2 as sole electron donor and O2 as electron acceptor (“knallgas” reaction)
Both gram-negative and gram-positive representatives known
Contain one or more hydrogenase enzymes that function to bind H2 and use it to either produce ATP or for reducing power for autotrophic growth
Most are facultative chemolithotrophs and can grow chemoorganotrophically
Some can grow on carbon monoxide (CO) as electron
donor (carboxydotrophs)

32. Hydrogen Bacteria
Figure 15.13

33. Characteristics of Common Hydrogen-Oxidizing Bacteria

34. 5. Methanotrophs and Methylotrophs
Organisms that can grow using carbon compounds that lack C-C bonds [(CH3)2N (trimethylamine)HCOO- (formate), CH3OCOO CH3 (Dimethyl carbonate), (CH3)2SO (dimethyl sulfoxide), CH3OH (methanol), CH3NH2 (methylamine), CH3)2NH (dimethylamine)]
Most are also methanotrophs – use CH4
Methanotrophs
Use CH4and a few other one-carbon (C1) compounds as electron donors and source of carbon
Widespread in soil and water
Obligate aerobes
Morphologically diverse

35. 5. Methanotrophs and Methylotrophs
Methanotrophs (cont'd)
Methanotrophs methane monooxygenase
Which incorporates an atom of oxygen from O2 into methane to produce methanol
Methanotrophs contain large amounts of sterols
Classification of Methanotrophs
Two major groups:
Type I
Type II
Contain extensive internal membrane systems for methane oxidation

36. 5. Methanotrophs and Methylotrophs
Type I Methanotrophs
Assimilate C1 compounds via the ribulose monophosphate cycle
Gammaproteobacteria
Membranes arranged as bundles of disc-shaped vesicles
Lack complete citric acid cycle
Obligate methylotrophs
Type II Methanotrophs
Assimilate C1 compounds via the serine pathway
Alphaproteobacteria
Paired membranes that run along periphery of cell

37. Electron Micrographs of Methanotrophs
Type I membrane system
Methylococcus capsulatans (β-Proteobacteria)
Carbon asimilation pathwy: ribulose
monophosphate pathway
Type II membrane system
Methylosinus (α Proteobacteria)
Carbon assimilation pathway: serine
Lookup the metabolic pathways for Methylomonas methanica (type II) and Methylococcus capsulatans (type 1) in KEGG (
Figure 15.14

38. Some Characteristics of Methanotrophic Bacteria

39. 5. Methanotrophs and Methylotrophs
Ecology and Isolation of Methanotrophs
Widespread in aquatic and terrestrial environments
Methane monooxygenase also oxidizes ammonia;
competitive interaction between substrates
Certain marine mussels have symbiotic relationships with methanotrophs

40. III Aerobic & Facultatively Aerobic Chemoorganotrophic
Proteobacteria
1. Pseudomonads including Pseudomonas
2. Acetic Acid Bacteria
3. Free-Living Aerobic Nitrogen-Fixing Bacteria
4. Neisseria, Chromobacterium, & Relatives
5. Enteric Bacteria
6. Vibrio, Alivibrio, and Photobacterium
7. Rickettsias

41. 1. Pseudomonads including Pseudomonas
Key Genera:
Pseudomonas
Burkholderia
Zymomonas
Xanthomonas
All genera are:
Straight or curved rods with polar flagella
Stain gram negative Chemoorganotrophs
Obligate aerobes
Posses polar flagella
Phylogenetically, the group is scattered within the Proteobacteria

42. Typical Pseudomonad Colonies – eg Burkholderia cepacia
Lophotrichous polar flagella
Figure 15.16a
Figure 15.16b

43. 1. Pseudomonads including Pseudomonas
Members of the genus Pseudomonas and related genera can be defined on the basis of phylogeny and physiological characteristics
Nutritionally versatile
Ecologically important organisms in water and soil
Some species are pathogenic
Includes human opportunistic pathogens and plant pathogens
Refer to the next two slides for an over view

44. Subgroups and Characteristics of Pseudomonads

45. Pathogenic Pseudomonads

46. Genus Zymomonas
Genus of large, gram-negative rods that carry out vigorous fermentation of sugars to ethanol
Used in production of fermented beverages

47. 2. Acetic Acid Bacteria
Organisms that carry out complete oxidation of alcohols & sugars
Leads to the accumulation of organic acids as end products
Motile rods
Aerobic
High tolerance to acidic conditions
Commonly found in alcoholic juices
Used in production of vinegar
Some can synthesize cellulose
Colonies can be identified on
CaCO3 agar plates containing ethanol

48. 3. Free-Living Aerobic Nitrogen-Fixing Bacteria
A variety of soil microbes are capable of fixing N2 aerobically
Distributed in alpha, beta and gamma Proteobacteria
The major genera of bacteria capable of fixing N2 nonsymbiotically are Azotobacter, Azospirillium, and Beijerinckia
Azotobacter are large, obligately aerobic rods; can form resting structures (cysts)
All genera produce extensive capsules or slime layers; believed to be important in protecting nitrogenase from O2 (nitrogenase is oxygen-sensitive)

49. Azotobacter vinelandii
Cells
(2 um)
Cysts
(3 um)
Azotobacter vinelandii
Figure 15.18

50. Slime producing Nitrogen2-fixing Bacteria
Beijerinckia species produce colonies with abundant slime
Cells of Derixia gummosa encased in slime
Slime producing Nitrogen2-fixing Bacteria
Figure 15.19a

51. Beijerinckia indica (PHB is present)
Derixia gummosa
Beijerinckia indica (PHB is present)
Acid-tolerant, free-living N2 fixing bacteria live in acid soils

55. 4. Neisseria, Chromobacterium, and Relatives
Neisseria, Chromobacterium, and their relatives can be isolated from animals, and some species of this group are pathogenic.
N. gonorrhoeae – gonorrhea
N. meningitidis – fatal inflammation of brain membrane
4. Neisseria, Chromobacterium, and Relatives

56. Characteristics of the Genera of Gram-Negative Cocci

57. Chromobacterium violaceum – produces violacein, a purple pigment
Structure of the aromatic compoun, violacein
Colony showing purple colour
Figure 15.21a

58. 5. Enteric Bacteria (Fam. Enterobacteriaceae)
Relatively homogeneous phylogenetic group within the Gammaproteobacteria
Facultative aerobes
Motile or non-motile, nonsporulating rods
Possess relatively simple nutritional requirements
Ferment sugars to a variety of end products
Enteric bacteria can be separated into two broad groups by the type and proportion of fermentation products generated by anaerobic fermentation of glucose
Mixed-acid fermentators
2,3-butanediol fermentators

59. Enteric Fermentations
Figure 15.23a

60. Diagnostic tests and differential media are often used to identify various genera of enteric bacteria

61. Key Diagnostic Reactions Used to Separate Enteric Bacteria

62. Key Diagnostic Reactions Used to Separate Enteric Bacteria

63. A Simple Key to the Main Genera of Enteric Bacteria
Figure 15.24

64. Escherichia
Universal inhabitants of intestinal tract of humans and warm-blooded animals
Synthesize vitamins for host
Some strains are pathogenic – cause health problems
Enteropathogenic (EPEC) – surface K antigens allows attachment & colonisation
Enterhemorrhagic (EHEC) – food / water, O157:H7
(O = CW, somatic, LPS; H = flagella proteins)

65. Salmonella and Shigella
Closely related to Escherichia (DDH > 50 & 70% respectively)
Usually pathogenic
S. typhi - typhoid
Salmonella is characterized immunologically by 3 surface antigens: (used for tracking epidemics)
O antigens
H antigens
Vi antigens, outer polysaccharide layer; typing S. typhi

66. Proteus Genus containing rapidly motile cells; capable of swarming
Frequent cause of urinary tract infections in humans

67. Butanediol fermentators – Enterobacter, Klebsiella & Serratia are a closely related group of organisms
Serratia
produces secondary metabolite, prodigiosin, a red pigment
isolated from water, soil, insect / vertebrate guts, human intestine.
S. marcescens:
human pathogen
infections from medical procedures
contaminant in intravenous fluids

68. Reactions Used to Separate 2,3-Butanediol Producers

69. 6. Vibrio, Alivibrio, and Photobacterium
The Vibrio Group
Cells are motile, straight or curved rods
Facultative aerobes
Possess a fermentative metabolism
Best known genera are Vibrio, Alivibrio & Photobacterium
Most inhabit aquatic environments
Some are pathogenic
Some are capable of light production (bioluminescence)
Catalyzed by luciferase, an O2-dependent enzyme
Regulation is mediated by population density (quorum sensing)

70. Bacterial Bioluminescence
Light emission
Most are marine isolates (Vibrio, Alivibrio, Photobacterium) but some terrestrial
May colonise specialized light organs of some maring fish & squids or on dead skin of crustacean / fish
V. cholera & V. vulnificus are pathogens; care when handling luminous bacteria
Bioluminescence only when oxygen is present
LuxCDABE gene products, luciferase, oxygen and a population density response (acyl homoserine [AHL], quorum sensing) is required

71. Bioluminescent Bacteria as Light Organ Symbionts
Figure 15.27c
Figure 15.27f
Figure 15.27a

72. 7. Rickettsias Rickettsias Small, coccoid or rod-shaped cells
Mostly obligate intracellular parasites; small genome size
Cannot grow outside a host cell; do not survive long outside the host
Causative agent of several human diseases
Typical procaryotic cell structure
7. Rickettsias

73. Small 0. 3um cells in tissue culture (a). EM of R
Small 0.3um cells in tissue culture (a). EM of R. popilliae growing in a vacuole in the host beetle, Melolontha melolontha (b)
Figure 15.28a
Figure 15.28b

74. Characteristics of Rickettsias

75. Wolbachia Genus of rod-shaped Alphaproteobacteria
Intracellular parasites of arthropod insects
Affect the reproductive fitness of hosts

76. IV Morphologically Unusual Proteobacteria
1. Spirilla
2. Sheathed Proteobacteria: Sphaerotilus & Leptothrix
3. Budding and Prosthecate/Stalked Bacteria

77. 1. Spirilla Group of motile, spiral-shaped Proteobacteria:
Spirillum & relatives
Magentospirillum
Bdellovibrio
Key taxonomic features include
Cell shape and size
Number of polar flagella
Metabolism
Physiology
Ecology

78. Spirilla : Spirillum Volutans
Figure 15.30a

79. Magnetotactic Spirilla
Highly motile
Isolated from freshwater habitats
Magnetotactic movement – directed by magnetic field
Fe304 magentosome & Fe3S4 (greigite)

80. Bdevellovibrio (leech)
Prey on other bacteria
Obligate aerobes
Members of Deltaproteobacteria
Widespread in soil and water, including marine environments
Figure 15.33a

81. Developmental Cycle of Bdellevibrio Bacteriovorus
Figure 15.33b

82. Attachment and Penetration of a Prey Cell by Bdellevibrio
Figure 15.32a

83. 2. Sheathed Proteobacteria: Sphaerotilus & Leptothrix
Sheathed Bacteria
Filamentous Betaproteobacteria
Unique life cycle in which flagellated swarmer cells form within a long tube or sheath
Under unfavorable conditions, swarmer cells move out to explore new environments
Common in freshwater habitats rich in organic matter

84. Sheathed Proteobacteria: Sphaerotilus & Leptothrix
Nutritionally versatile
Able to use simple organic compounds
Obligate aerobes
Cells within the sheath divide by binary fission
Eventually swarmer cells are liberated from sheaths

85. Sphaerotilus Natans
Figure 15.34a

86. Sphaerotilus Natans
Figure 15.34b

87. Sphaerotilus Natans
Figure 15.34c

88. Sheathed Proteobacteria: Sphaerotilus & Leptothrix
Sphaerotilus and Leptothrix are able to precipitate iron oxides

89. Leptothrix and Iron Precipitation
Figure 15.35

90. Budding and Prosthecate/Stalked Bacteria
Large and heterogeneous group
Primarily Alphaproteobacteria
Form various kinds of cytoplasmic extrusions bounded by a cell wall (collectively called prosthecae)

91. Features of Stalked, Appendaged and Budding Bacteria

92. Prosthecate Bacteria
Figure 15.36a

93. Prosthecate Bacteria
Figure 15.36b

94. Prosthecate Bacteria
Figure 15.36c

95. Cell Division
Figure 15.37

96. Budding and Prosthecate/Stalked Bacteria
Budding Bacteria
Divide as a result of unequal cell growth
Two well-studied genera
Hyphomicrobium (chemoorganotrophic)
Rhodomicrobium (phototrophic)

97. Stages in the Hyphomicrobium Cell Cycle
Figure 15.38

98. Morphology of Hyphomicrobium
Figure 15.39a

99. Morphology of Hyphomicrobium
Figure 15.39b

100. Budding and Prosthecate/Stalked Bacteria
Prosthecate and Stalked Bacteria
Appendaged bacteria that attach to particulate matter, plant material, and other microbes in aquatic environments
Appendages increase surface-to-volume ratio of the cells

101. Stalked Bacteria
Figure 15.40a

102. Stalked Bacteria
Figure 15.40b

103. Stalked Bacteria
Figure 15.40c

104. Budding and Prosthecate/Stalked Bacteria
Caulobacter
Chemoorganotroph
Produces a cytoplasm-filled stalk
Often seen on surfaces in aquatic environments with stalks of several cells attached to form rosettes
Holdfast structure present on the end of the stalk used for attachment
Model system for cell division and development

105. Growth of Caulobacter
Figure 15.41

106. 15.16 Budding and Prosthecate/Stalked Bacteria
Gallionella
Chemolithotrophic iron-oxidizing bacteria
Possess twisted stalk-like structure composed of ferric hydroxide
Common in waters draining bogs, iron springs, and other environments rich in Fe2+

107. The Neutrophilic Ferrous Iron Oxidizer, Gallione Ferruginea
Figure 15.42a

108. The Neutrophilic Ferrous Iron Oxidizer, Gallione Ferruginea
Figure 15.42b

109. V. Delta- and Epsilonproteobacteria
Gliding Myxobacteria
Sulfate- and Sulfur-Reducing Proteobacteria
The Epsilonproteobacteria

110. 15.17 Gliding Myxobacteria Gliding Gliding Bacteria
A form of motility exhibited by some bacteria
Gliding Bacteria
Are typically either long rods or filaments
Lack flagella, but can move when in contact with surfaces

111. Classification of the Fruiting Myxobacteria

112. Classification of the Fruiting Myxobacteria

113. 15.17 Gliding Myxobacteria Myxobacteria
Group of gliding bacteria that form multicellular structures (fruiting bodies) and show complex developmental life cycles
Deltaproteobacteria
Chemoorganotrophic soil bacteria
Lifestyle includes consumption of dead organic matter or other bacterial cells

114. 15.17 Gliding Myxobacteria
Fruiting myxobacteria exhibit complex behavioral patterns and life cycles
Vegetative cells are simple, nonflagellated rods that glide across surfaces and obtain their nutrients primarily by lysing other bacteria and utilizing released nutrients
Under appropriate conditions, vegetative cells aggregate, construct fruiting bodies, and undergo differentiation into myxospores

115. Myxococcus
Figure 15.43a

116. Myxococcus
Figure 15.43b

117. Stigmatella aurantiaca
Figure 15.44a

118. Stigmatella aurantiaca
Figure 15.44b

119. Fruiting Bodies of Three Species of Fruiting Myxobacteria
Figure 15.45a

120. Fruiting Bodies of Three Species of Fruiting Myxobacteria
Figure 15.45b

121. Fruiting Bodies of Three Species of Fruiting Myxobacteria
Figure 15.45c

122. 15.17 Gliding Myxobacteria
The life cycle of fruiting myxobacterium is complex

123. Life Cycle of Myxococcus xanthus
Figure 15.46

124. Swarming in Myxococcus
Figure 15.47a

125. Swarming in Myxococcus
Figure 15.47b

126. Fruiting Body Formation in Chondromyces crocatus
Figure 15.48a

127. Fruiting Body Formation in Chondromyces crocatus
Figure 15.48b

128. Fruiting Body Formation in Chondromyces crocatus
Figure 15.48c

129. Fruiting Body Formation in Chondromyces crocatus
Figure 15.48d

130. Sulfate- and Sulfur-Reducing Proteobacteria
Dissimilative sulfate- and sulfur-reducing bacteria
Over 40 genera of Deltaproteobacteria
Use SO42- and So as electron acceptors and organic compounds or H2 as electron donors
H2S is an end product
Most obligate anaerobes
Widespread in aquatic and terrestrial environments

131. Sulfate- and Sulfur-Reducing Proteobacteria
Physiology of sulfate-reducing bacteria
Group I
Oxidize lactate, pyruvate, or ethanol to acetate and excrete fatty acid as an end product
Group II
Oxidize fatty acids, lactate, succinate, and benzoate to CO2

132. Sulfate- and Sulfur- Reducing Bacteria

133. Enrichment Culture of Sulfate-Reducing Bacteria
Figure 15.49g

134. The Epsilonproteobacteria
Abundant in oxic–anoxic interfaces in sulfur-rich environments
e.g., hydrothermal vents
Many are autotrophs
Using H2, formate, sulfide, or thiosulphate as electron donor
Pathogenic and non-pathogenic representatives

135. Characteristics of Key Genera of Epsilonproteobacteria